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 presents the results and gained experiences from the Project Based Learning (PBL) of magnetic component design within a Power Electronics Course. PBL was applied during the laboratory exercises through a design-project task based on a boost converter test board. The students were asked to calculate the main boost converter's circuit parameters' capacitor C and inductor L, and then additionally required to design and build-up the inductor L, in order to meet the project's goals. The whole PBL process relied on ideas from the CDIO (Conceive, Design, Implement, Operate), where the students are encouraged to consider the whole system's process, in order to obtain hands-on experience. PBL is known to be a motivating and problem-centered teaching method that gives students the ability to transfer their acquired scientific knowledge into industrial practice. It has the potential to help students cope with demanding complexities in the field, and those problems they will face in their future careers.
This paper deals with the implementation of a control algorithm based on a state controller with an adaptation of the state controller gains by using the fuzzy-logic approach. Adjustable state controller gains cause that the static error can be reduced arbitrarily for a system with variable parameters as is the DC-DC step-down converter for power supply systems. Fuzzy sets are tuned offline by a genetic algorithm using fuzzy-logic and a genetic toolbox in MATLAB. Fuzzification and defuzzification algorithms are implemented in real time within a Field Programmable Gate Array circuit. The whole control algorithm is performed within a sampling time of 5.33 µs. Operation of the controller is verified experimentally.
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