Research on the application of on-board energy storage on an electric locomotive for quarry railway transport

Methods of using on-board energy storage system on rolling stock are considered. Their use ensures a reduction in energy consumption and reduces the impact on the environment. Concepts of managing energy flows in the traction system of an electric rolling stock equipped with onboard energy storage systems are considered. It is proposed to apply the concept of control on an electric locomotive for quarry railway transport, which consists in reducing the current consumption from the traction network during the acceleration of the rolling stock and compensating the power during movement with the lowest voltage on the current receiver. For the selected control concept, a simulation of the train movement on the test section was carried out while varying the value of the limit current consumed by the electric locomotive from the traction network. The power of the energy storage device and its working energy capacity is determined. Based on the results of the study, it is justified to limit the current consumed by the electric locomotive of the traction network at the level of 600 A.


Introduction
Increasing the efficiency of quarry railway transport is an important direction for achieving the goals of decarbonization and sustainable development of mining enterprises.
A well-known method of increasing the efficiency of electric traction systems is the use of recuperation [1].For this, it is necessary to use energy storage systems in the electric traction system.For electric traction systems of quarry transport, it is expedient to use on-board energy storage systems (OESS), because, firstly, it allows the most effective use of recuperation energy, and secondly, it provides the possibility of autonomous movement of electric rolling stock in non-electrified sections.
The concept of managing energy flows in the electric traction system is important for the effective use of OESSs.The analysis of the sources shows that the structure and parameters of the traction electric drive and OESS depend on the type of rolling stock and its operating conditions [2].
Nowadays, several types of an electric rolling stock equipped with OESS are in operation.The traction electric drive MITRAC Energy Saver [3] is designed for use in urban electric transport.OESS is built using supercapacitors.Discharge of the supercapacitor occurs when the tram accelerates.During electrodynamic braking and at a stop, the OESS is charged.The EV-E301 regional railcar train of Japan's JR East [4] operates on a route that has a non-electrified section.The strategy of control is as follows: when moving along an electrified section, the traction and auxiliary systems of the train are powered and the OESS is charged from the catenary network.When moving through a non-electrified section, the traction and auxiliary systems of the train are powered by the OESS.During electrodynamic braking, auxiliary systems are powered and OESS is charged.At the stop, auxiliary systems are powered and the OESS is charged from the contact network.Accumulators are used in OESS.
A feature of the Flexity 2 tram system developed by Bombardier for Nanjing [5] is that the contact network is available only near the stops.Therefore, the operating algorithm of the OESS is similar to that described above: when moving under the contact wire, the tram accelerates and the OESS is charged.Movement between stops is carried out with the power supply of the traction and auxiliary systems from the OESS.OESS is built using accumulators.
The tram system of the CAF development in Birmingham [6] functions similarly.The OESS of the rolling stock is built based on supercapacitors.
When the BEC-819 train, created by Hitachi [7] is moving in the traction mode, the traction and auxiliary systems are powered from the contact network through active rectifiers.There is no energy exchange with the OESS in this mode.When moving in coasting mode, charging of the OESS from the contact network begins.In the mode of electrodynamic braking, the OESS is charged.When moving along non-electrified areas, traction and auxiliary systems are powered by OESS.
The Combino Plus tram manufactured by Siemens [8] is equipped with a hybrid OESS, which includes batteries and supercapacitors.During acceleration, the tram systems are powered by supercapacitors.Power is supplied from the batteries in the driving mode with speed maintenance or coasting.During electrodynamic braking, supercapacitors are charged.At the stop, batteries and supercapacitors are recharged from the contact network.
Let's consider the algorithms of OESS operation on autonomous rolling stock.
A diesel train produced by Hitachi [9] uses battery-based OESS.OESS feeds the traction and auxiliary system during acceleration.After a speed of 30 km/h, a diesel generator connects, which provides energy to the diesel train system.During electrodynamic braking, OESS is charged.At a stop, auxiliary systems are powered from the OESS.
The tram produced by CRRC for Tangshan [10] is equipped with fuel cells and hybrid OESS.The fuel cell works with a certain power during the entire movement.When accelerated, the traction system is additionally powered by supercapacitors.In steady motion mode, if necessary, the traction system is powered by batteries.During electrodynamic braking, supercapacitors are charged.At the stop, OESS is recharged from fuel cells.
To ensure long-term autonomous movement of rolling stock on non-electrified sections, as well as in the case of a battery power source, OESS is built based on batteries of various types [11][12][13][14][15].For the most part, this rolling stock is in trial operation, including checking and finalizing OESS management strategies.
It is worth noting that inertial energy accumulators were used on rolling stock [16,17].However, their exploitation was more of an experimental nature and they did not become widespread.
A generalization and analysis of energy exchange control concepts for electric traction systems can be found, for example, in [18][19][20].Here we note that one of the methods of controlling the OESS consists in reducing the current consumption from the main power source during the acceleration of the rolling stock and ensuring optimal operating modes of the main power source.This OESS concept of control can be applied to an electric locomotive for quarry railway transport and is based on the following.
Observation of the operation of traction units at mining enterprises shows that the voltage on their current receivers can significantly decrease -down to a minimum voltage equal to 7.5 kV in the case of an alternating current electric traction system.Mostly, this happens when a loaded train is moving uphill.To prevent the minimum voltage protection from triggering, the control system or the driver limits the electric locomotive's current consumption from the traction network.As a result, the speed of the train decreases, and the passage time of the section increases.
To eliminate the above situation, it is possible to use an OESS, which, in case of reaching a certain value of current that the electric locomotive consumes from the catenary network, will feed the traction electric drive and auxiliary systems.Thus, there is a problem with researching the processes of energy exchange in the traction system of an electric locomotive with an onboard OESS while limiting the current consumed from the contact network and determining the parameters of the OESS.

Research material and results
Direct modeling of the processes of energy consumption by an electric locomotive with an asynchronous traction electric drive during the movement of a train on a section of the track will not ensure high reliability of the results, since the traction network has a complex topology, its parameters cannot be determined with high accuracy, the nature of the movement of trains along the feeder zone is random.Therefore, let's assume that the movement of the electric locomotive under study in the section takes place at a voltage of 7.5 kV, that is, it is carried out at the minimum value of the voltage on the current receiver.Such a scenario corresponds to the worst conditions of the power supply of electric rolling stock.
The current consumed from the contact network is determined both by the mode of operation of the traction electric drive and by the power consumed by auxiliary systems.Let's assume that when a certain value of the current consumed by the electric locomotive from the contact network is exceeded, the OESS must be connected to power its systems.We will calculate the power and working capacity of the OESS at different limit values of the current that can be consumed from the network.
For example, let's study the electric locomotive described in [21].Its traction characteristic is shown in figure 1a, and the profile of the section from the crushing plant to the reloading point is shown in figure 1b.given in [22], was used.With its help, the dependence of the tangential power was received for the case of the movement of a loaded train from the loading point to the crushing plant (figure 2).One of the variants of the structure of the traction system of the electric locomotive under study, in which power compensation from the OESS is ensured, is shown in figure 3.Here the intermediate circuit, to which the traction electric drive and auxiliary systems are connected, is fed jointly from the input converter and the OESS.The power flow management algorithms are as follows.
In traction mode (figure 4a), the power consumed from the traction network is determined through the active component.If the total load is a tangential power and auxiliary systems, exceed this power, then the OESS is connected to the power supply of the load.
In the electrodynamic braking mode (figure 4b), the energy coming from the traction electric drive can be used to power the auxiliary systems of the electric locomotive (priority use), charge the OESS, and recuperate into the traction network (in case there is an excess of the total power of the auxiliary systems and the power, with which the energy storage (ES) is charged).If there is not enough energy to power auxiliary systems, the rest is compensated from the traction network.If during braking, the power coming from the traction electric drive exceeds the total power of auxiliary systems and OESS, the excess energy is recovered to the traction network.At the same time, the latter is possible if there is an OESS power limit.on-board energy storage system, ES -energy storage, BC -matching converter, AUX -auxiliary systems, PC -power that is consumed from the traction network, P DC1 -power that enters the intermediate circuit from the input converter, P DC2 -the power that comes from to the intermediate circuit from OESS, POESS -power that is consumed from ES, P DC3 -power that is transmitted to the traction electric drive, P DAU X -power consumed by auxiliary systems, P ktangent power of the electric locomotive, P DC3 -power that comes from the traction electric drive, P DC2 -the power that is transferred to the OESS, P DC1 -the power consumed from the traction network in EDB mode.
To perform the calculations by the above, energy flow management algorithms were developed, the block diagram of which is shown in figure 5.The diagram does not show the calculation of the energy that is recovered to the traction network.
As mentioned above, two scenarios of operation are possible in EDB mode.
In the first scenario, the capacity of ES is sufficient to store all available energy.In this case, the power must ES meet the condition where P Lnom -nominal tangent power of the electric locomotive, η T D -the efficiency of "traction converter -electric motor -reduction gear" is taken as equal to 0.9; η BC -the efficiency of the matching converter of the OESS assuming to be equal to 0.9.
The second scenario foresees that the storage capacity is selected from the condition of power compensation in traction mode.The storage capacity in this case is calculated using where η 1 -the efficiency of the "traction transformer -input converter -filter" link is taken as 0.95; P AU X -the power of auxiliary systems of the electric locomotive is assumed to be equal to 300 kW, U C -the lowest voltage on the current receiver, equal to 7.5 kV, I CA -the limit current consumed by the electric locomotive from the traction network.Figure 6 shows the dependence of the power of the ES (figure 6a) and the working energy capacity of the ES (figure 6b) on the limited current consumed by the electric locomotive.The calculations have been provided for the limit current range of 400...1000 A. The power of the ES and the working energy capacity were determined during the calculations.The corresponding dependencies are shown in figure 6.
The analysis of dependencies in figure 6 shows that in the first scenario -determination of the OESS power from the condition of complete energy absorption in the EBD mode -the ES power is a constant value.The working energy capacity in this case has a non-linear character with a minimum of about 600 A.
For the second scenario -determining the power of the energy storage device from the condition of power compensation while limiting the current consumption -the power is ES a linear dependence.The dependence of the working energy capacity is non-linear, and in the current range of 600...800 A it has a shade with an almost constant value.It should be noted that the power values calculated according to (1) and ( 2) at a certain value of the limit current of the electric locomotive give the limits of the range in which the power can be ES.If the power is ES less than calculated by expression (2), then the power compensation mode will not be provided.If the ES power is greater than calculated according to (1), then there will be an irrational use of ES, since this value is the maximum ES power with which it can work in the case under study.
Thus, the determination of ES power and working energy capacity requires additional research.In general, both determining the parameters of the ES and determining the parameters of the entire traction system is a complex task [23][24][25].
Regarding the determination of the limit current of an electric locomotive, which can be consumed by an electric locomotive from the catenary network, the following must be taken into account.
1.A system of copper contact wire and a bimetallic supporting cable is used in the contact suspension on the quarry railway transport.The continuous current of the PBSM-95+MF-100 contact network is 660...820 A depending on the degree of wear of the contact wire [26,27], while an increase in current by 1.3 times is allowed if the duration of its flow does not exceed 3 minutes.Since the actual degree of wear of the contact wire is unknown, and, in addition, there may be several electric locomotives on one feeder zone, it is advisable to take the limiting current close to the lower limit of the range.2. It is shown in [21] that when moving along the investigated section of the track, the movement of an electric locomotive with nominal power in the traction mode is carried out only uphill, and most of the time -70.5% of the total time of movement in the traction mode -the traction drive operates with a power that does not exceed 1500 kW.The maximum value of the tangent power on flat areas is 3500 kW, which is 52.2% of the nominal power.That is, in speed maintenance modes, about 50% of the power of the electric locomotive is sufficient.Based on this, the current of the electric locomotive will be where P k -tractive power, which is equal to 3500 kW; U 1 -the voltage on the current receiver, equal to 7.5 kV; η -efficiency factor of the electric locomotive, which can be taken as equal to 0.86, cos ϕ -the factor of the fundamental harmonic, which is assumed to be equal to 0.95.After performing the calculations, we will get that the fundamental harmonic of the network current of the electric locomotive is about 570 A. 3. Decreasing the limit current of the electric locomotive leads to a reduction in the powerand therefore the cost -of the traction transformer of the input converter and the filters associated with it.However, it leads to an increase in the power and capacity of the OESS.Since the cost of electrical equipment is unknown, this aspect is not taken into account when determining the limiting current.
Thus, by comparing the first two aspects and the results of the calculation of the ES parameters, the limit current of the electric locomotive can be taken as equal to 600 A.
For example, figure 7 shows the dependencies of the change in the energy of the ES (a), its power (b), and the current consumed by the electric locomotive from the catenary network (c).The current limit is set to 600 A.
As can be seen from figure 7, when a current of 600 A is reached, the ES "switches on" to work.This happens during acceleration and movement on hills.In the EDB mode, when driving downhill, braking at the end of the movement, the energy enters the ES and even returns to the contact network.At the same time, the current that the electric locomotive consumes from the contact network does not exceed 600 A. Thus, the algorithm described above can be used to determine the parameters of the onboard energy storage during working with current limitations.It is rational to simulate the movement of the train during the entire half-passage, as well as maneuvering during loading and unloading if during these operations the power is supplied from the onboard energy storage.To improve the accuracy of calculation results, it is necessary to improve mathematical models, in particular, to determine the losses in the traction electric drive.

Conclusions
The concepts of onboard energy storage management have been analyzed.Their use on rolling stock allows for storing of the energy during braking, which is later used during the movement of rolling stock.
For the electric locomotive of quarry railway transport, it is proposed to implement the mode of operation to limit the current consumed by the electric locomotive from the catenary network, and the energy exchange processes for this method of control have been investigated.
Calculations have been made and a justification has been provided for determining the limit current that can be consumed by an electric locomotive from the catenary network.Restriction of the limit current to 600 A is rational for the electric locomotive under study.

Figure 1 .
Figure 1.Traction characteristics of the electric locomotive (a) and profile of the track section (b).

Figure 2 .
Figure 2. Dependence of the tangential power of the electric locomotive.

Figure 4 .
Figure 4. Energy flows in the traction system of an electric locomotive is traction mode (a)and EBD mode (b): P -pantograph, IC -input converter, TD -traction electric drive, OESSon-board energy storage system, ES -energy storage, BC -matching converter, AUX -auxiliary systems, PC -power that is consumed from the traction network, P DC1 -power that enters the intermediate circuit from the input converter, P DC2 -the power that comes from to the intermediate circuit from OESS, POESS -power that is consumed from ES, P DC3 -power that is transmitted to the traction electric drive, P DAU X -power consumed by auxiliary systems, P ktangent power of the electric locomotive, P DC3 -power that comes from the traction electric drive, P DC2 -the power that is transferred to the OESS, P DC1 -the power consumed from the traction network in EDB mode.

Figure 5 .
Figure 5. Block diagrams of the energy flow management algorithm in the traction system of the electric locomotive.

Figure 6 .
Figure 6.Dependencies of power (a) and and working energy capacity (b) of the energy storage (green line -scenario 1, red line -scenario 2).

Figure 7 .
Figure 7. Dependencies of changes in energy (a), power (b) of the energy storage, and current consumed by the electric locomotive from the catenary network (c).