## 4 Discussion  
In the present study, the stochastic signal was used as the driver signal in the investigation of transient processes caused by a variation in the traction drive feed voltage. In the investigation of transient processes caused by a variation in the load on the traction drive shaft, the driver signal was the impulse signal. This circumstance could be explained by the following factors:  
Objective difficulties when obtaining the experimental data on the dependence of the voltage at the input of the autonomous voltage inverter, accounting for the stochastic character of variation on the current collector of the electric rolling stock, on the noises caused by a variation of the temperature modes of the autonomous voltage inverter and traction motor;  
The character of variation of the load at the attempt of wheel slippage of one-wheel pair of the rolling stock was not investigated. Investigations of the effect of asymmetry of the feed voltage system and traction drive windings on the starting characteristics were conducted without taking into account the weight of the train and locomotive. This was due to the fact that the accounting of the train and locomotive weight would lead to an increase in the time of transient processes in the traction drive system, while the character of starting characteristics would remain the same in the steady-state mode. The transient temperature processes were not taken into account in the investigation of the effect of temperature on the starting characteristics. This circumstance was due to the fact that the electrodynamic processes would last for a few minutes even if the weight of the train and locomotive were taken into account, while the temperature transient processes would last for a few dozen minutes. The amplitudes of phase currents and flux linkages of the stator were chosen as the diagnostic criteria, although just one diagnostic criteria, i.e., phase flux linkages of the stator, would have been sufficient for the detection of asymmetric emergency modes in the traction drive system. This approach would have been appropriate only for mere confirmation of the presence of the asymmetric emergency modes. A criterion would have been sufficient for the identification of the location of occurrence of the defect acting on the emergence of asymmetric emergency modes. This particularly applies to the case where the asymmetric modes also occur on both the inverter arms and the motor windings. This also involves defects occurring on different phases of the autonomous inverter and traction drive (Figure 8). In the study of the effect of motor winding asymmetry and power system asymmetry, the dependencies of the phase currents on the degree of motor winding fault and the degree of voltage asymmetry of the power system were obtained. The nature of the dependencies obtained is consistent with the results of similar studies [45; 46; 47; 48]. Results consistent with those reported in [39; 40; 41] for similar studies were obtained when investigating the effect of stochastic variations in load and inverter supply voltage on the nature of variations in motor stator currents. The adjustments introduced into the structure \"Observer of torque and flux\" would not only enable organization of a system of operative diagnostics for the presence of asymmetric emergency modes in the DTC traction drive system, but also improve the accuracy of control in the presence of asymmetric modes caused by a variation in the values of the feed voltage and load on the traction drive shaft. The authors carried out the research on an electric locomotive traction motor, i.e., a high-power motor. However, the results obtained are also valid for less powerful motors. This may be explained by the fact that asynchronous motors of different power have the same physics. Nevertheless, further investigation is necessary to explore this issue.