The formation and propagation of ionising waves in impulsive overvolted gas discharges for parallel plane electrode geometry is studied. The spatio-temporal evolution of the electronic and ionic densities together with the space-charge distorted field was thoroughly examined for different initial electron distributions. The study elucidates the important role of the electrons present ahead of both the anode and cathode ionising waves and shows particularly how the wavefront profile evolves during its propagation. In all cases, provided that the discharge gap is sufficiently large, the wavefront is transformed into an electron shock wave defined by a shock zone of extremely high electronic density and field gradients. This limits the domain of validity of the gas discharge models that neglect both the thermal diffusion of charge carriers and gas photoionisation of photodetachment.

The authors propose a macroscopic model for gas breakdown ionising waves based on a consistent hydrodynamic system of equations describing the spatio-temporal evolution of particle density, momentum and energy. They apply this model to investigate the properties of the electron shock zone situated at the head of a discharge channel, so that it can in particular predict the non-equilibrium electron temperature as distinguished from the static equilibrium electron temperature. The temperature dependence of macroscopic coefficients can be predicted from the available electron transport and ionisation data. Their previous analysis (1980) of the role of the photoionisation in a gas discharge is extended to the case of fast electron shock waves by taking into account the finite lifetime of the molecular excited states. This shows that the gas photoionisation process cannot have an important role in fast breakdown waves except at low gas pressures. Finally, this study analyses the different possible causes of a non-equilibrium electron energy.

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Induction motors (IM) that are driven using the conventional direct torque control algorithm (DTC) suffer from vital drawbacks which are high ripples in the torque and flux. These ripples result due to the use of a look-up table and hysteresis comparators which causes variable switching frequency. Moreover, the use of a traditional two-level inverter leads to the production of low-quality voltage and current. The work presented in this paper proposed a modified control system to overcome these drawbacks. The proposed control system is based on the use of the space vector modulation-based DTC algorithm (DTC-SVM) for driving three-phase IM via a three-level T-Type inverter. The conventional DTC-SVM algorithm has been modified to match the work of the proposed inverter. The modification process was based on the mapping of the standard DTC-SVM algorithm in the space vector of the three-level inverter. The conventional and the modified control systems are implemented using MATLAB/Simulink package. The comparison of the standard and the modified DTC-SVM has been performed by simulation. Simulation results showed the superiority of the proposed algorithm in terms of reducing ripple in torque and flux and improving the quality of current and voltage supplied to the motor.

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