Improving the Reliability of a Microprocessor-Controlled Electric Drive

Electric drives are used in industrial installations for the mechanical movement of various kinds of goods, in pumps, as well as in transport installations to bring them into motion. An electric drive includes an actuator (motor) and a frequency converter, as well as a control system that provides soft start, reverse and speed control. The most complex part of the electric drive is the frequency converter, so the probability of the occurrence of a failure of the entire system depends on its reliability. Currently, inverters are used, based on a three-phase bridge with IGBT transistors; its circuitry has made it possible to minimize the number of elements, which was especially relevant earlier when using thyristors with forced switching. Currently, they are replaced by fully controllable insulated gate transistors, which reduced the number of elements in power circuits, and also simplified control algorithms - thereby increasing the reliability of electric drives in general. However, a further improvement in the characteristics of the electric drive is still associated with the improvement of the frequency converter. In this paper it is proposed to replace the three-phase bridge circuit in the inverter with three single-phase channels according to the full-bridge circuit in each of them; the phase outputs are connected in series according to the star circuit. The main difference between this option is the presence of a common neutral at the inverter output, the tap from which is not present in three-phase bridge circuits. In this case, in the event of an accident in one of the phases, it is possible to connect the corresponding phase of the motor to the inverter neutral, which, when correcting the shift angle between the remaining two phases of the inverter by an angle of 60°, ensures the formation of a symmetric three-phase voltage system on the motor stator. This made it possible to abandon the reservation of a three-phase bridge circuit, requiring two sets of 3 phases each on the motor stator, provided that their neutrals were isolated, and such systems are essentially six-phase. The electric drive described in this article has redundancy that is not inferior to the currently used systems and has several advantages - these include maintaining 2/3 of the rated power during emergency phase shutdown, and the operation of the electric motor in symmetric mode; also the advantages include the possibility of forming a three-level voltage without capacitors in the DC link. In general, the proposed solution has a low cost while maintaining reliability, as well as the quality of voltage and currents in nominal mode.