A Flexible Discontinuous Modulation Scheme with Hybrid Capacitor Voltage Balancing Strategy for Three-Level NPC Traction Inverter

Multilevel inverters are now-a-days being applied in electric vehicles (EV). Considering the dynamic operating conditions of an EV propelled by an induction motor, this paper proposes a flexible discontinuous modulation strategy for three-level neutral-point-clamped (NPC) inverter that can shift modulation pattern seamlessly from sinusoidal pulsewidth modulation (SPWM) to discontinuous PWM (DPWM). The modulation scheme is generalized at each degree of discontinuity to ensure minimum switching losses for variable load power factors. Additionally, a hybrid voltage balancing strategy, which comprises two sets of compensating offset signals with complementary features, has been introduced to mitigate voltage deviation problem at neutral point of the inverter. The unique feature of the proposed hybrid balancing approach is that it generates uniform compensating neutral current regardless of the level of discontinuity. This results in identical and predictable voltage balancing dynamics for the entire modulation transition covering SPWM and DPWM. It has been shown that the proposed hybrid balancing strategy does not lose its unbalance compensation strength even during transition from one modulation pattern to another. The effectiveness of the proposed scheme for wide variations in operating conditions is studied through extensive simulation, and validated in experimentation using a prototype NPC inverter with induction motor loads

An Improved Modulation Strategy for Fast Capacitor Voltage Balancing of Three-Level NPC Inverters

This paper presents an improved pulsewidth modulation strategy in conjunction with an optimal compensator for fast capacitor voltage balancing in three-level neutral-point-clamped (NPC) inverter. The voltage balancing compensator is designed in such a way that it produces optimal unbalance compensation coefficient according to the inherent limitations related to the variability range of modulating signals. It generates maximum compensating neutral current for the full modulation depth extending into overmodulation region and throughout the entire range of load power factor angles, and thus improves the unbalance compensation ability for all the operating conditions of the inverter. The optimal compensation offset signal corresponding to each operating point is determined from the boundary limit of the auxiliary modulating signals. Particle swarm optimization is applied for such purpose. The performance of the proposed optimal compensator for different combinations of modulation index and load power factors are evaluated through extensive simulation study using Matlab/Simulink and validated in experimentation using a threelevel NPC inverter prototype with induction motor load. Finally, the voltage balancing performances of the proposed compensator are compared with that available in literature to confirm the usefulness of the proposed concept

Comparative study between different optimisation techniques for finding precise switching angle for SHE-PWM of three-phase seven-level cascaded H-bridge inverter

Selective harmonic elimination pulse-width modulation (SHE-PWM) works at low-frequency switching, which reduces switching losses, device stress, and increases energy conversion efficiency. So, it can be an effective control strategy for multilevel inverter working on medium-voltage, high-power industrial energy conversion application. It provides desired output voltage by retaining the requested fundamental component as well as eliminating some low-order harmonics. The application of SHE-PWM in industries is having an influence on precise solvability of complex and non-linear equations. This study presents two recently reported optimisation techniques, namely backtracking search algorithm and differential search algorithm (DSA) for obtaining a more accurate solution of the harmonics elimination problem. The superiority of the proposed optimisation algorithms over the well known ancient algorithm such as genetic algorithm, BEE algorithm and particle swarm optimisation have been established by a comparative study with respect to the possibility of attaining global minima, the rank of convergence rate, and inverter performance analysis. Simulation and experimental results validate the efficacy of the DSA optimisation technique for calculating more precise switching angles that totally eliminate 5th- and 7th- order harmonics with fulfilling the requested fundamental component

Arsenic-Induced Mitochondrial Instability Leading to Programmed Cell Death in the Exposed Individuals

InWest Bengal, India, more than 6 million people in nine districts are exposed to arsenic through drinkingwater. It is regarded as the greatest arsenic calamity in the world. Arsenic is a well-documented human carcinogen, which does not induce cancer in any other animal model. Interestingly, at lower concentrations, arsenic is known to induce apoptosis in various cancer cell lines in vitro. We have studied apoptosis in human peripheral blood mononuclear cells (PBMC) of 30 arsenic exposed skin lesion individuals by annexin V-FITC staining and compared with 28 unexposed individuals. The percentage of apoptotic cells in individuals with skin lesions was significantly higher (p < 0.001) in comparison to unexposed individuals. In the exposed individuals with skin lesions, there were elevated levels of intracellular reactive oxygen species (ROS), mitochondrial membrane permeability and increased cytochrome c release, leading to increased downstream caspase activity. Arsenic-induced DNA damage was confirmed by DNA ladder formation and confocal microscopy. We also observed that chronic arsenic exposure reduced Bcl-2/Bax ratio and also resulted in cell cycle arrest of PBMC in G0/G1 phase. All these observations indicate that mitochondria-mediated pathway may be responsible for arsenic-induced apoptosis