Alenka Hren

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.