Franc Mihalič

The efficiency of the wireless power transfer (WPT) using a half-bridge inverter on the transmitter side can be increased by switching from frequency modulation (FM) to pulse density modulation (PDM). The method of generating PDM, described and implemented in this paper is based on a sliding mode controller (SMC), which also serves as a transmitter coil current controller. The current controller is in a cascade with the output voltage controller, which can be implemented either on the transmitter or on the receiver side.

For a DC-AC converter (inverter), a key element in renewable power supply systems, an output voltage of sinusoidal shape is required to assure a high-quality sustainable energy flow. Thus, through the modulation process, this property must be “incorporated” into the output voltage. This operation incurs some harmonic distortion into the inverter output voltage, which can have an undesired influence on the load. In the single- or three-phase systems (grid-connected, uninterrupted power supply systems (UPS) or motor drives), the high quality Total Harmonic Distortion (THD) factor must be considered; the voltage harmonic content also must be limited. This paper provides a comprehensive spectrum analysis of a three-level output voltage in singlephase inverter. The output voltage is generated by triangular Sinusoidal Pulse-Width Modulation (SPWM) and, by using the Fourier analysis, Bessel functions and trigonometric equality, the high harmonic components are extracted in a straightforward analytical way. Finally, the overmodulation phenomenon is also considered, and the procedure is experimentally validated.

All electric vehicles are the only way to decarbonize transport quickly and substantially. Although multilevel inverters have already been used in some transportation modes, they are rarely used in road transportation, especially in light-duty passenger BEVs. With the transition to a high 800-V DC link to extend the driving range and enable extreme fast charging, the possibility of using multilevel inverters in commercial light-duty passenger BEVs becomes feasible. Higher efficiency, higher power density, better waveform quality, lower switching frequency, the possibility of using low-rated switches, and inherent fault tolerance are known advantages of multilevel inverters that make them an efficient option for replacing 2-level inverters in high DC link passenger BEVs. This paper discusses high DC link voltage benefits in light-duty passenger BEVs, presents the state-of-the-art of different conventional multilevel inverter topologies used in BEVs, and compares them with conventional 2-level inverters from different aspects and limitations. Based on commercial upper-class passengers’ BEV data and a review of multilevel inverters on the market, future trends and possible research areas are identified.

The design of modern industrial products is further improved through the hardware-in-the-loop (HIL) simulation. Realistic simulation is enabled by the closed loop between the hardware under test (HUT) and real-time simulation. Such a system involves a field programmable gate array (FPGA) and digital signal processor (DSP). An HIL model can bypass serious damage to the real object, reduce debugging cost, and, finally, reduce the comprehensive effort during the testing. This paper provides a historical overview of HIL simulations through different engineering challenges, i.e., within automotive, power electronics systems, and different industrial drives. Various platforms, such as National Instruments, dSPACE, Typhoon HIL, or MATLAB Simulink Real-Time toolboxes and Speedgoat hardware systems, offer a powerful tool for efficient and successful investigations in different fields. Therefore, HIL simulation practice must begin already during the university’s education process to prepare the students for professional engagements in the industry, which was also verified experimentally at the end of the paper.

In single-phase inverter systems (grid-connected, Uninterrupted Power Supply systems or motor drives), the high quality Total Harmonic Distortion (THD) factor must always be considered, along with the utilization rate of the DC link. In cases when the supplying DC voltage is reduced, the output voltage can still be assured constant in a limited range by using over-modulation. Unfortunately, this operation incurs fundamental frequency related higher order harmonics’ force (especially the third is dominant) into the inverter output voltage, which is a huge drawback in almost all applications. This paper provides a comprehensive spectrum analysis of three-level output voltage in a single-phase inverter working in over-modulation regime. The output voltage is generated by triangular Sinusoidal Pulse-Width Modulation (SPWM) and, based on the analytical results of a frequency spectrum evaluation, the opposite third harmonic component in the modulator unit forces this component in the output voltage close to zero. Other remaining higher harmonics can be attenuated more easily by using a smaller filter. Although the voltage gain of the fundamental harmonic component is lower at higher over-modulation, such a solution assures lower THD in the wide inverter’s working range. The proposed SPWM procedure was validated experimentally.

This paper addresses improved electromagnetic compatibility (EMC) in switched-mode power converters (SMPCs), without using electromagnetic interference (EMI) filters. A practical solution is proposed for minimizing conductive EMI in a pulsewidth modulated (PWM), and random PWM dc-dc power converters. A comparative investigation is performed into the use of different random modulation schemes (driven by the DSP-2 board with the TMS320C32) as against the normal PWM. The effectiveness of randomization on spreading those dominating frequencies that normally exist in constant frequency PWM schemes is evaluated by power spectral density (PSD) estimations in the low-frequency range. Some parasitical- and topology-based EMI sources in devices are presented and frequency analysis is shown by using the discrete Fourier transform (DFT). SPICE simulations are also used to verify practical solutions for eliminating negative EMI sources and achieving EMC improvements. Finally, levels of conductive EMI are estimated with DFT, and experimentally verified to comply with the CISPR 25 (or EN 55025) regulations. Moreover, it is clearly shown, that limited speed PWM driving of the power switches with appropriate snubber circuits guarantees reduced conductive EMI. When considering the price and high EMC, in the final solution the power converter is driven by the mu-controller PIC16F876 with limited numerical and peripheral capabilities, where only normal PWM and randomized PWM can be implemented