Operating parameters of electric rolling stock on railway sections

. The introduction of energy storage systems on motor rolling stock in order to improve the energy efficiency of the transportation process is not possible without performing preliminary calculations and experimental studies to determine the operating modes of the electric rolling stock. As a result of the work performed to process data on ED4M series electric trains on various sections of operation at different ambient temperatures, the dependences of electric power consumption for heating and auxiliary needs of the electric train were obtained. The average electricity consumption for traction and the return of electricity in case of regenerative braking is estimated. The main parameters of the energy storage device have been determined in the first approximation.


Introduction
It is well known that suburban electric trains operate year-round in a variety of climatic conditions. In this regard, suburban companies are trying to improve the comfort and convenience of their passengers so as not to lose out to competition with the fast-growing other modes of transport. Undoubtedly, comfort is warm in electric train cars during the cold season and air conditioning during the warm season, which entails an increase in the total electricity consumption of an electric train. The Russian Railways is committed to introducing and developing energy-saving technologies in all of its structural divisions. One interesting solution to improve the energy efficiency of commuter services could be the use of energy storage systems in rolling stock. To determine the parameters of such systems, it is necessary to study the operation modes of electric rolling stock (ERS) in more detail by conducting experimental research.

Object and methods of research
A distinction is made between passive and active experiments. For passive experiments, as we know, there are only factors in the form of input controllable but uncontrollable variables. The task of planning experimental research in this case is reduced to the optimal organisation of information collection and solving such issues as the choice of, e.g. the number and frequency of measurements, the choice of the method for processing the results of measurements, etc. It is this type of experiment that was carried out in the research, the results of which are presented in the article.
The information obtained for a number of ED4M series electric trains from the operational depot allows us to present the obtained measurements of electricity consumption for traction (for heating, auxiliary needs and recuperation) in coordinates plot -temperature (month, travel speed) and assess their nature of change. The suitability of the approximation can be evaluated according to the following basic criteria [1][2][3]: -sum of squares of errors (SSE) determined by the formula: Here k y is an observed value in k x ; k y y is a predicted value in k x .

SSE R SST
Here SST is a total sum of squares, determined according to the formula: Here yis an average value of the variable y . A refined value of the mixed correlation square (Adj R 2 ): Here n is a data number; m is a number of model parameters k x .
A standard error of estimation (RSME)

SSE RSME n m
As an approximation method we will use the locally weighted regression method, which is used to approximate nonlinear dependencies between variables [4,5]. The method is nonparametric and provides a good basis for fitting a smooth surface between the results. Figure 1 shows the electricity consumption for electric train traction depending on the operating section and month (a), and on the operating section and outside temperature (b). The dependencies of electricity consumption on the above variables (Figure 1) are poorly described by fitted surfaces, as evidenced by the sum of the squares of errors (SSE) and the mixed correlation square (R 2 ) presented in Table 1 (option 1 and 2). However, Figure 1 shows that the highest electricity consumption corresponds to the section Omsk-Tatarskaya, Tatarskaya-Omsk and is approximately at the level of 2000 kW•h. Minimum consumption of electrical energy corresponds to the section Omsk-Irtyshskaya, Irtyshskaya-Omsk and corresponds to the level of 750 kW•h.  Figure 2 shows the dependence of electric train heating energy consumption on operating section and month (a), outdoor temperature (b). The surfaces fitted are described significantly better than the previous ones. Mixed correlation squares R 2 is 0.64 and 0.68, respectively (Table 1,  The highest electricity consumption for car heating also corresponds to the Omsk-Tatarskaya, Tatarskaya-Omsk section and is at the level of 600 kW•h. Minimum electricity consumption is observed on the Omsk-Isilkul, Isilkul-Omsk and Omsk-Irtyshskaya, Irtyshskaya-Omsk sections with consumption levels around 200 kW•h.

Results
Electricity consumption for auxiliary needs has a typical doubling from October till March (Fig. 3) and is comparatively identical for all sites, however the obtained surfaces are also poorly described ( Table 1). The highest electricity consumption is at 100 kW•h and the lowest at 30 kW•h. The main parameters that determine the operating mode of the energy storage system are: rated power, energy capacity, overload capacity, charge and self-discharge times, depth of discharge, operating life and capital cost. To determine these parameters, the operating characteristics of the ERS must be taken into account. In order to identify the limit operating modes, let's consider the graph of current consumption and voltage level at the current collector of ED4M electric train at the circulation sections ( Figure 5).

Conclusions
As a result of the research to assess the level of electricity consumption for traction by motor rolling stock, for heating its cars, the level of electricity return due to the application of regenerative braking, the electricity consumption for auxiliary needs are determined depending on the operating areas and the outside air temperature. The suitability of the approximation was determined, and it was found that temperature has the greatest impact on electricity consumption for heating, and a seasonal increase in electricity consumption by a factor of two for the auxiliary needs of the electric train was traced. A detailed analysis of the electric train load schedule identifies the maximum and minimum values of voltage at the electric train current collector, maximum and minimum values of current of motor cars. For the Omsk-Nazyvaevsk, Nazyvaevsk-Omsk operation section, operating modes of the electric train and their duration were determined, which, taken together, makes it possible to estimate the main parameters of the energy storage system. In general, for this section, it should be said that the modes of operation of the energy storage system will be of a short-term nature. The average duration of operation in the charge mode will be 60 s, and the amount of energy returned by the rolling stock determining the energy capacity is on average from 5.5 to 7.3 kWh, with a maximum power of 0.8 MW.