Development of the converter structure that enables power supply to traction induction motors of mine electric locomotives from different levels of voltage

Abstract

We have proposed an adjustable structure of the converter of energy of electric drive in the electrotechnical complex of a mine electric locomotive from power sources with different voltage levels ‒ from a contact network and a battery of traction accumulators. A characteristic feature of the converter is the presence of inverter units that can be connected either sequentially or in parallel. When powered by a low­voltage source, inverter units are connected in parallel over the entire range of change in the output voltage. When powered by a high voltage source, inverter units are connected sequentially in the range of low output voltages and in parallel in the range of high output voltages. Such an approach makes it possible to align the power voltage levels of traction asynchronous motors of a mine electric locomotive at a lower level. The expected alignment of voltage levels is carried out at a lower level compared to a standard circuit of the three­phase bridge autonomous inverter and is achieved by controlling the paired bridges in the power circuit of traction induction motors. Given this, the frequency of voltages of width­pulse modulation does not change, which is important for the process of reducing dynamic losses of power in the drive’s elements. It has been confirmed that an increase in the output voltage distortion coefficient in the IGB­transistors of the inverter with the minimal level of energy losses in the electric drive’s elements is achieved by modulating the voltage at a constant switching frequency at different voltage levels. We have proven the fact that the best indicators for the harmonic coefficient were obtained at frequencies about 30 Hz, which are the working ones, so the converter operating mode is most effective at these frequencies. The result of analysis of the classical scheme of the inverter has revealed that increasing the frequency of pulse­width modulation by three times significantly increases electrical losses in the windings of traction electric motor. In the proposed circuit of the voltage inverter of engine’s power, at leveling the voltage at low level, there is no need to increase the frequency of pulse­width modulation, which does not lead to a growth in the electrical losses in a traction motor.