R. Barlik

Pulse Width Modulation methods for bidirectional/high-performance Z-source inverter

In this paper issue of pulse width modulation (PWM) methods for bidirectional/high-performance Z-source inverter (ZSI) is presented. Due to additional switch operating with the Z-network frequency an approach is different than in basic version of ZSI. Three various PWM methods are discussed: the state-of-the-art maximum constant boost control (MCBC), maximum constant boost control with discontinuous reference (DMCBC) and highly optimized minimum switching number (MSN). All methods are described in details and compared on the base of simulation test in SABER package and investigations of laboratory model of bidirectional ZSI. Impact of applied PWM method on inverter design process is also analysed - key issue is selection of passive elements (especially Z-network and line filter inductors).

Design and Evaluation of Reduced Self-Capacitance Inductor in DC/DC Converters with Fast-Switching SiC Transistors

The paper presents an inductor with reduced self-capacitance, designed and evaluated with fast-switching SiC transistors in dc-dc converters. A conventional inductor with the same core and number of turns was also build for comparison. The two inductors are tested experimentally on two different 2 kW, 100 kHz dc-dc converters with silicon carbide switches-one with a junction field-effect transistor (JFET) and the other with a bipolar junction transistor (BJT). Replacing the conventional inductor with the one that has lower self-capacitance improved the switching performance of the converter and reduced its electromagnetic emissions. Furthermore, the efficiency of the converter is improved-in the case of the JFET boost converter the power losses were reduced by 16% and by 20% in the case of BJT.

Measurement of temperature sensitive parameter characteristics of semiconductor silicon and silicon -carbide power devices

In this paper, results of laboratory investigation of representative samples of semiconductor silicon and silicon carbide power devices, such as PiN diode, Shottky diode, IGBT and JFET, are presented. With use of a thermal chamber the characteristics of temperature sensitive parameters for selected types of devices were determined by measurements within the range 25 - 150degC. The measurement was done using short pulses, which are not able to change measured temperatures. The results have to enable identification of junction temperature in the case of other tests, especially those oriented on energy losses, efficiency, and thermal management.

Output currents equalization for parallel connected three-phase PWM buck rectifiers

The three-phase PWM buck rectifier with wide output voltage range seems to be a promising solution for renewable energy sources. When the demanded nominal power is greater than single rectifier capability, the paralleling of converters is necessary. Furthermore, a proper modulation strategy allows the reduction in size of the LC filter. But in the case of parallel converters a symmetrical distribution of the power load must be guaranteed. Because of transformer-less connection it is highly probable that DC currents become unbalanced as a result of non-identical elements and input voltages distortions. Therefore, an algorithm is required to keep output currents differences inside the acceptable bandwidth. Based on the example of two parallel-connected PWM buck rectifiers, the paper describes output current balancing methods with mean values of the output voltages correction. After a theoretical background, a universal equalization algorithm is presented. Results of the tests conducted on a modular system 2/spl times/2 kVA rectifiers controlled by fixed point TMS320F2812 confirms the flexibility of the proposed solution.

Silicon carbide inverter with two series Z-networks

The paper presents a concept of the three-phase DC/AC inverter with two impedance networks connected in series (2×Z) built with only Silicon Carbide power devices. Authors describe features of the novel inverter with special attention on serious reduction of voltages on applied Z-network capacitors. Benefits from application of SiC devices: JFETs and Schottky diodes are also discussed. Design and construction of the 2kVA/3×400V RMS laboratory model is shown. Finally, authors prove concept by simulation and experimental tests at 100kHz switching frequency.

Computer simulations for two angular-speed-control systems of a current source inverter feeding an induction machine

This paper presents the simulation results of two types of control system for an induction machine, fed by a PWM current source inverter with a capacitive output filter. The vector control scheme was applied in both cases. In one system, control of stator phase current vector takes place through an intermediate signal of the stator current frequency. This signal is determined by the load angle proportional-integral (PI) controller. In the second system, stator phase current is directly controlled, thanks to synchronization of the modulator with respect to stator flux. Though the output filter capacitors of PWM current source inverters (CSI) causes some difficulties in forcing rapid changes in machine currents and voltages, the systems presented herein are characterized by good dynamic properties.

Three-phase AC-DC unidirectional PWM multiple-switch rectifier topologies-selected properties and critical evaluation

This paper takes a critical look at existing unidirectional multiple-switch rectifier topologies with an aim of giving a comparative analysis and simple classification. Since power factor correction and harmonic distortion of the line currents remain issues of high priority in the field of power conversion and utilization, the rectifiers considered herein, some of which are derived from DC chopper circuits i.e. switch-mode power supplies, may fulfil these conditions without additional complex control systems. The chopper derived topologies have an additional advantage of cost effectiveness in comparison to naturally commutated line converters or six-switch bi-directional PWM converters. Included are converters with and without transformer coupling. Since the selection of a particular topology depends on various factors such as efficiency, cost effectiveness, simplicity, type of load or application, the desired power density etc., the paper aims at pointing out the essential considerations for a clear and accurate design, application and selection criteria. Simulation results of selected topologies are also presented. Where possible, solutions based on practical circuits have been quoted as an aid to resolving associated technological problems.

Experimental evaluation of GaN Gate Injection Transistors

The paper presents experimental evaluation of Gate Injection Transistors produced on the base of Gallium Nitride (GaN). Authors show double-pulse test results and measurements of the half-bridge converter with inductive load. Obtained results indicate very good performance of new devices which are able to operate at high switching frequency and low power losses (0.6% losses of converter power at 150 kHz was achieved). Streszczenie. Artykul przedstawia ocene w trybie eksperymentu tranzystorow typu Gate Injection Transistor zbudowanych na bazie azotku galu (GaN). Autorzy prezentują wyniki testow dwupulsowych a takze wyniki pomiarow ukladu polmostka obciązonego dlawikiem. Wyniki wskazują na bardzo dobre parametry nowych przyrządow, charakteryzujących sie niskimi stratami mocy nawet przy duzych czestotliwościach przelączen (uzyskano 0.6% strat mocy przeksztalcanej przy 150kHz) (Ocena w trybie eksperymentu azotkowo-galowych tranzystorow typu GIT).

Design and evaluation of reduced self-capacitance inductor for fast-switching SiC BJT dc/dc converters

The paper presents design, measurements and evaluation of the inductor with reduced self-capacitance. As an reference inductor with the same parameters but non-optimized self-capacitance is chosen. Differences in the parasitic capacitance of the inductor are validated by four measurement methods and experimentally confirmed on a 2 kW, 100 kHz dc/dc converter with silicon carbide BJTs. When the low-capacitance inductor is applied the switching performance is better, especially high-frequency resonances are limited. Additionally, it was found that the power losses were reduced by approximately 20%.

Fault Protection System for Current Source Inverter with Normally on SiC JFETs

This paper describes a simple fault protection system for Current Source Inverter built with normally-on SiC JFETs. Because all transistors are in on-state after loss of the gate drive(s) supply, list of possible fault modes is extended in reference to standard inverters. That is also why an additional normally off switch is introduced in the DC link. Operation principles of the protection system which follows the drain-source voltages of JFETs and the current of the DC link are presented. The 2kVA/100kHz model of the inverter equipped with the proposed system is validated via various laboratory tests including short-circuits and the auxiliary supply turn off.