Features of Space Vector Pulse Width Modulation in 5-Phases Cascaded High Voltage Converters

The purpose of this work is to analyze the capabilities of space-vector pulse-width modulation when controlling a 5-phase high-voltage cascade frequency converter in normal mode and several types of emergency situations. Taking into account the large number of controlled power transistors, an asynchronous modulation method is proposed, based on calculating the amplitude values of individual phases at each time based on the duty cycle of space vectors, which allows the control system to use independent switching in each phase. In emergency modes, when individual H-bridges are damaged, it is proposed to use the balanced space vectors method, which ensures the symmetry of the electromagnetic field in the event of a short circuit of both individual cascades and one or two phases of the inverter. Methodology. We use a mathematical and geometric interpretation of variable amplitude space vectors when projecting voltages onto a symmetrical 5-phase load. Results. Analysis of the 1st harmonic of phase voltages showed that the use of the space vector modulation method in the normal operating mode of a 5-phase converter makes it possible to increase the utilization factor of DC voltage sources by 23.1% (instead of 15.6% for a 3-phase converter). If individual H-bridges fail and the voltages in the load phases are balanced, the utilization factor may decrease, but in any case it will remain greater than 1. In this case, the higher harmonics, despite significant distortions in the shape of the phase voltages, are mutually compensated in the electromagnetic field of the load, as evidenced by absence of pulsations and shocks on the graphs of transient processes of the electromagnetic torque of the engine. Balancing of the electromagnetic field in the load is maintained even if one or two phases of the inverter are short-circuited. This significantly increases the survivability of the electric drive, which is especially important in critical mechanisms and technological processes, where converters are used. The article presents calculation formulas, phase voltage graphs and simulation results for a 5-phase permanent magnet motor, explaining the principles of operation in normal and emergency situations, which can be used in the design of the converter control system.