This study presents a novel linear approximated methodology for full alternating current-optimal power flow (AC-OPF). The AC-OPF can provide more precise and real picture of full active and reactive power flow modelling, along with the voltage profile of buses compared to the commonly used direct current-optimal power flow. While the AC-OPF is a non-linear programming problem, this can be transformed into a mixed-integer linear programming environment by the proposed model without loss of accuracy. The global optimality of the solution for the approximated model can be guaranteed by existing algorithms and software. The numerical results and simulations which represent the effectiveness and applicability of the proposed model are given and completely discussed in this study.

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Multilevel converters are growing fast, whereas industry needs particular tools to evaluate efficiency and performance of such converters. This study focuses on the analysis and practice of power losses in a three-level neutral-point clamped (NPC) inverter. First, a precise mathematical model for three-level inverters is introduced to be used for simulating power losses of the switches, providing AC voltage and current of each phase, voltage and current of the switches as well as both the conduction and switching losses. Further, an NPC inverter was developed to validate the analytical work by comparing experimental results with those of simulations. Additionally, the thermal modelling of semiconductors is obtained using datasheet parameters. Then, the temperature rise is further modelled using the power losses along with the thermal model in the form of RC ladder. Finally, the lifetime of semiconductors is predicted using the heating curves in line with the power-cycling concept. The measured power losses and temperatures in comparison with the presented model suggest this kind of research as an applicable replacement for expensive measuring devices.

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Hysteresis Current Control (HCC) is widely used due to its simplicity in implementation, fast and accurate response. However, the main issue is its variable switching frequency which leads to extraswitching losses and injecting high-frequency harmonics into the system current. To solve this problem, adaptive hysteresis current control (AHCC) has been introduced which produces hysteresis bandwidth which instantaneously results in smoother and constant switching frequency. In this paper the instantaneous power theory is used to extract the harmonic components of system current. Then fixed-band hysteresis current control is explained. Because of fixed-band variable frequency disadvantages, the adaptive hysteresis current control is explained that leads to fixing the switching frequency and reducing the high-frequency components in source current waveform. Due to these advantages of AHCC, the switching frequency and switching losses will be diminished appropriately. Some simulations are done in MATLAB/Simulink. The Fourier Transform and THD results of source and load currents and the instantaneous switching frequency diagram are discussed to prove the efficiency of this method. The Fourier Transform and THD results of source and load currents are discussed to prove the validity of this method.