Method of Space Vector Pulse Width Modulation in High Voltage Cascaded Frequency Converter with Damaged H-cells

Abstract

The paper proposes a control method for a high-voltage cascade frequency converter with H-bridges, based on Space Vector Pulse Width Modulation, regardless of the number of normal and damaged H-cells in phases. Analytical dependencies are given that explain the principle of balancing asymmetric base vectors, and tabular data are provided for the implementation of this method in most possible emergency modes in 4-6-level frequency converters. It was found that the formation of control laws for power switches only taking into account the change in length and phase shifts between the base vectors in emergency modes is not enough to exclude shock electromagnetic and electromechanical processes in an induction motor. Such shocks occur due to the appearance of an additional shift of the phase-to-phase voltages due to the asymmetry of the phase voltages on the half-period of the generated signal. Based on the expansion in a Fourier series, the necessary correcting phase shifts are calculated for all considered emergency modes. Modelling of electromagnetic and electromechanical processes in an electric drive 3.3 MW, 6.6 kV with a 6-level frequency converter has shown the effectiveness of the developed method – during transitions from a normal to an emergency mode, electromagnetic processes caused by phase shifts are excluded. At the same time, SVPWM in all modes increases the energy efficiency of power supplies by 15.6%, which makes it possible to increase the phase-to-phase voltage by 10 ... 26% in emergency modes in comparison with sinusoidal PWM. The proposed analytical dependencies and tabular data can be used in the synthesis of control systems with both scalar and vector control.