This thesis investigates the possibilities for increasing the power conversion efficiency and power density of a single-phase single-stage AC-DC converter with power factor correction capability. Initially, the limitations are investigated for simultaneous increase of power density and efficiency in hard switched bidirectional converters. The switching frequency dependent turn-on losses of the transistors have been identified as the main limiting factor. In order to avoid the increase in total power losses with increasing the switching frequency, a control approach is proposed for achieving zero voltage switching transitions within the entire operating range of a bidirectional converter that utilizes power transistors in a bridge structure. This approach is based on operation in the discontinuous conduction mode with a variable switching frequency. Operation in the discontinuous conduction mode ensures the necessary reversed current that naturally discharges the parasitic output capacitance of the transistor and thus allows this transistor to be turned on at zero voltage. On the other hand, the varying switching frequency ensures that the converter operates close to the zero voltage switching boundary, which is defined as the minimum required current ripple at which zero voltage switching can be maintained. Operation with the minimum required current ripple is desirable as it generates the lowest magnetic core losses and conduction losses within the power circuit. The performance and effectiveness of the investigated approach were initially verified in a bidirectional DC-DC converter. A reliable zero voltage switching was confirmed over the entire operating range of a bidirectional DC-DC converter, as well as the absence of the reverse recovery effect and the unwanted turn-on of the synchronous transistor. In order to justify its usage and demonstrate its superior performance, the proposed zero voltage switching technique was compared with a conventional continuous conduction mode operation which is characterized by hard switching commutations. After successful verification and implementation in a bidirectional DC-DC converter, the investigated zero voltage switching approach was adapted for usage in an interleaved DC-AC converter with power factor correction capability. Comprehensive analysis of the converter's operation in discontinuous conduction mode with a variable switching frequency was performed in order to derive its power loss model. The latter facilitated the design process of the converter's power circuit. A systematic approach for selecting the converter's power components has been used while targeting for an extremely high power conversion efficiency over a wide operating range and a low volume design of the converter. The final result of the investigations performed within the scope of this thesis is the interleaved AC-DC converter with power factor correction capability. Utilization of interleaving allows for increasing the converter's power processing capability, reduces the conducted differential mode noise and shrinks the range within which the switching frequency has to vary. The proposed zero voltage switching control approach was entirely implemented within a digital signal controller and does not require any additional components within the converter's circuit. The experimental results have confirmed highly efficient operation over a wide range of operating powers. A peak efficiency of 98.4 % has been achieved at the output power of 1100 W, while the efficiency is maintained above 97 % over the entire range of output powers between 200 W and 3050 W.
D.09 Tutoring for postgraduate students
COBISS.SI-ID: 281705984The presented two-axis controller allows simplified and rapid implementation of laboratory experiments in robotics and similar applications. The controller is based on a powerful DSP processor TMS320F28335, which can implement control of servomotors. Design and implementation of control algorithms include usage of floating point calculations. The system is programmable in Matlab/Simulink environment. The electronic controller circuitry design enables a robust operation of the controller even in industrial conditions. Functional extensions of the controller are possible with the internal communication interface. The controller was applied within the European FP7 HYPSTAIR project for an advanced HMI with a haptic interface of a light hybrid electric aircraft.
F.02 Acquisition of new scientific knowledge
COBISS.SI-ID: 11702100This article proposes a new control method for a pulse-density modulated microinverter and its implementation within a field programmable gate array circuit. The structure and operating principle of the studied microinverter demand implementation of a pulse-density modulationbased control method with two independent control loops. The first one ensures a constant input current from the source while the second one provides a sinusoidal voltage at the converter’s output. At the same time the implemented control method ensures zero-current switching of the utilized power transistors in decoupling and output stages which allows operation at high switching frequency. The performance of the proposed control method for a microinverter operating in island mode was experimentally verified in steady-state operation, as well as during load transients.
D.09 Tutoring for postgraduate students
COBISS.SI-ID: 19750678A serial hybrid drive allows two independent sources of energy, namely the battery system and the generator system. In case of failure of either component, the other can supply reserve power. Furthermore, the electric motor, which is the exclusive propulsion unit of a serial hybrid system, offers increased reliability and reduced maintenance compared to a piston-powered engine. In order to control the hybrid in a way that is both safe and energy efficient, a special human-machine interface shall be designed, developed and validated. The interface allows pilot to intuitively exploit all the benefits of hybrid propulsion while at the same time reduces pilot’s workload as compared to managing a piston engine.
D.01 Chairing over/coordinating (international and national) projects
In this patents a medium-frequency resistance spot welding system which is used for welding metal sheets is described. This system consists of a frequency converter, a transformer, a diode rectifier, a welding gun and metal sheets. Voltage pulses of different lengths can be generated by the frequency converter. This voltage is than used to supply the welding transformer. Consequently, different methods of generating these voltage pulses can be used. The most common method used in the industry is the pulse-width modulation, which generates voltage pulses with the selected modulation frequency. This frequency is usually constant and equal to the rated frequency of the transformer. However, the pulse width of the generated voltage can be changed even during the welding process based on the needs of the welding process.
F.33 Slovenian patent
COBISS.SI-ID: 21085974