Comparison of PWM Methods for Compensating for H-Cell Damage in Cascaded High-Voltage Frequency Converters

The work compares methods for controlling power switches of a multilevel cascade converter in normal and emergency
modes when one or more H-modules fail. It is shown that the phase-to-phase voltage balancing method, in which, in the
event of an accident of individual cascades, the rotation of the phase voltage vectors is carried out so as to preserve the
spatial position and the same amplitude of the phase-to-phase voltage vectors, ensures a decrease or even the absence of
motor torque jumps.
Conditions have been found for supplementing the carrier sinusoidal signal with a third harmonic, which ensure the most
efficient use of power supplies when two or more modules are damaged, and increase the voltage of the first harmonic
by 10...20% compared to sinusoidal pulse-width modulation. The modified method of space-vector modulation of basic
vectors also ensures the minimization of shock loads by limiting the amplitude of the desired vector at the level of the
radius of the circle inscribed in the hexagon formed by the vertices of the basic vectors with arbitrary amplitude and
position. This method makes it possible to increase the coefficient of use of power sources by 15.6%, regardless of the
number of damaged cells in each phase, which, compared to sinusoidal pulse-width modulation, increases the voltage of
the first harmonic by 10...26%. The method is best when one or two cells are damaged and during normal operation of
the converter, that is, in the most common cases.