CLAIM OF PRIORITY

[0001] This application claims priority to U.S. Patent Application No.

62/548,251 filed on August 21, 2017, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

[0002] This disclosure relates to energy recovery from rail systems.

BACKGROUND

[0003] Railway systems, for example, metropolitan or subway systems, employ conventional steel-on-steel wheel subway trains with two to six cars, powered by a third rail (for example, a 750 VDC rail) with return circuit through the running rails. A braking train generates energy that can be captured and re-used, for example, to power the same train or a different train or can be transmitted to an AC network, for example, a public AC utility grid.

SUMMARY

[0004] This specification describes technologies relating to hybrid wayside energy recovery systems.

[0005] [0001]Certain aspects of the subject matter described here can be implemented as a wayside energy recovery system for recovering energy from a traction power distribution network. The wayside energy recovery system includes a wayside energy transmission system coupled to a utility electrical grid and coupled to a traction power distribution network of a railway system on which rail vehicles operate. The wayside energy transmission system is configured to transmit energy recovered from the traction power distribution network to the utility electrical grid. The system includes a wayside storage system coupled to the railway system. The wayside energy storage system is configured to store energy recovered from the traction power distribution network. A controller is coupled to the traction power distribution network, the wayside energy transmission and to the wayside energy storage system. The controller is configured to receive positional information about a rail vehicle on the traction power distribution network and transfer at least a portion of energy recovered from the rail vehicle to either the wayside energy transmission system for transmission to the utility electrical grid or to the wayside storage system for storage based, in part, on the positional information about the rail vehicle.

[0006] This, and other aspects can include one or more of the following features. The controller can store the positional information about the rail vehicle. The positional information can include a schedule of the rail vehicle. The controller can transfer at least the portion of the recovered energy to either the wayside energy transmission system for transmission to the utility electrical grid or to the wayside storage system for storage based, in part, on the information associated with the utility electrical grid. The information associated with the utility electrical grid can include power rates and a voltage regulation. The controller can transfer all of the recovered energy to the wayside energy transmission system or to the wayside storage system. The system can include a wayside energy transmission controller operatively coupled to the wayside energy transmission system and to the controller, and that can receive, from the controller, an instruction specifying the portion of the recovered energy to be transmitted to the utility electrical grid and control the wayside energy transmission system to transmit the specified portion to the utility electrical grid. The system include a wayside energy storage controller operatively coupled to the wayside energy storage system and to the controller, and that can receive, from the controller, an instruction specifying the portion of the recovered energy to be stored and control the wayside energy transmission system to store the specified portion of the recovered energy.

[0007] The details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a schematic diagram of an example of a hybrid wayside energy recovery system. [0009] FIG. 2 is a flowchart of an example process of providing power to a wayside storage system of the hybrid wayside energy recovery system.

[0010] Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0011] Energy consumed in commuter or metro rail systems comes from utility electrical grids. Typically, a high voltage line will feed voltage from the utility electrical grid to one or more electrical substations through a metering point where the voltage is transformed by a transformer to approximately 35 kiloVolts (kV). The 3- phase 35 kV is then stepped down to a suitable voltage and then passively rectified to 750 V or 1500 V DC to be fed to a traction power distribution system. The traction power distribution system then makes the power available to be consumed by rail vehicles for acceleration and movement between passenger stations through a catenary direct current (DC) system.

[0012] During deceleration, the kinetic energy of the trains coming to a halt is dissipated in multiple areas, namely, rail and windage friction, regenerated to the DC catenary by inverting the power from the traction motors (where fitted with such systems), dissipated into electrical resistors aka "brake resistors" as heat energy. The energy regenerated into the DC catenary by a decelerating train would normally result in a rise of the DC bus voltage. For this reason, the nominal 750 V DC systems are designed to operate in the range of 600 - 900 V DC. The increase in the DC bus voltage can cause stress and performance limitations, reduce life of the associated equipment, and cause voltage sensitive devices and equipment to trip.

[0013] The energy storage and recuperation systems used to recover the deceleration energy are of two types - onboard and wayside. Onboard systems store the energy on the railcar and feed it to the systems onboard for traction or auxiliaries. Such systems are limited by the added weight to the rail vehicle and are often not effectively remunerative beyond a size. Consequently, such onboard systems are not capable of absorbing all the recoverable energy of braking. Wayside energy recovery systems are larger and fall into two types - storage and direct inversion (recuperation). [0014] Direct inversion (or inverter-based) systems have the simplicity of energy transfer to the utility electrical grid. However, the transfer needs a private AC line. Feed-in tariffs and incentives for rail energy recovered are unavailable in some places, and, where available, do not offset the investment in inverter systems. Also, in private networks, the transfer of energy takes place at a total efficiency of 90% with losses of 4%, 1%, 2%, 1% and 2% at the DC to inverter stage, inverter to HV transformer stage, HV transformer to transmission loss stage, transmission loss to LV transformer stage and LV transformer to rectifier stage, respectively, resulting in a loss of about 10% of saved energy. Because the energy is transferred through the main rectifier systems, the rectifiers can be overused and overworked. The energy recovery can be limited by the capacity of the AC line to accept surges of power for very short periods (for example, of the order of seconds). The circuit breakers and other connections can add to system cost.

[0015] Storage based systems have a storage element in addition to a DC-DC or DC-AC converter. Such systems have lesser power transfer efficiency compared to direct inversion systems. For example, flywheel-based energy storage systems experience losses of 4%, 4% (2 x 2%) and 4% at the DC to DC-AC inverter stage, DC- AC inverter to storage stage, and storage to AC-DC converter stage, respectively, resulting in a total loss of about 12%. In another example, supercap-based energy systems experience losses of 4%, 8% (2 x 4%) and 4% at the DC to DC-DC inverter stage, DC-DC inverter to storage stage, and storage to DC-DC inverter stage, respectively, resulting in a total loss of about 16%. Such systems are limited by storage capacity and experience some losses during storage. Such systems also require additional installation space, which may be large depending upon storage density. Costs for such systems can be high, in part, due to the need to change batteries and capacitors that have a limited life due to the number of cycles and operating temperatures.

[0016] This disclosure describes a hybrid wayside energy recovery system that combines features of the inverter-based system and the storage system. When there is no utility electrical grid available or the one available is incapable of absorbing spurts of energy transfer, the hybrid system can regulate the energy by storing and transferring the energy at a controlled rate. The system can work beyond the limitations of storage-based systems by recuperating the DC braking energy in excess of the storage capacity to the AC network, or when the instantaneous energy causes the current limit of the storage component to be exceeded. The system can transfer the stored energy to the AC line by mitigating the effects of peak demand on the AC line. There need be only one disconnect on the DC side for the inverter and the storage system, thereby lowering costs compared to a separate inverter or storage system. The hybrid system with storage element can bridge the energy transfer temporarily between the DC and the AC sides, allowing transfer of the AC energy to even the low voltage auxiliary users like escalators or HVAC system by avoiding power surges into the AC system. The system can provide a small footprint per energy savings and have a short payback time. When the schedule of the trains are programed into the hybrid storage system, the AC privet line can also be used to input to the storage energy at a slower rate to prepare the storage for discharge the energy for the trains that are leaving the station, this avoids over current chargers where apply, or insures the voltage to be more stable.

[0017] The intelligence built into the system with rail schedules, loading factors, power rate structure and schedules, and demand overages can enable the system to dynamically switch among the various modes of operation and automatically enhance the value of the recovered energy from time to time.

[0018] The hybrid recovery system 100 described here can incorporate both the storage and inversion components for wayside application with the following specificity of parameters: 750 V and 1500 V DC systems with regenerative railcars; inverters if there exists a private rail network ring for the rail system; DC traction line should be continuous through the rail line without the need for bridging; systems with headway between 100 seconds and 10 minutes; lines with 2- to 8-car trains; electrical substations serving one to four passenger station span; metros and light rails operating 16 hours or more and at average maximum speeds of 35 kilometers per hour (kph) or more.

[0019] FIG. 1 is a schematic diagram of an example of a hybrid wayside energy recovery system 100 for recovering energy from a traction power distribution network 114. The traction power distribution network 114 is coupled to a utility electrical grid 116 from which the traction power distribution network receives power which, as described above, is used to power a railway system on which rail vehicles operate. The traction power distribution network can also transmit power recovered from rail vehicles operating on the railway system to the utility electrical grid.

[0020] The hybrid recovery system 100 includes a wayside energy

transmission system coupled to the utility electrical grid 116 and coupled to the traction power distribution network 114. The wayside energy transmission system can transmit energy recovered from the traction power distribution network 114 to the utility electrical grid 116. As described above, the recovered energy is the energy generated by deceleration of one or more rail vehicles operating on the railways system.

[0021] The hybrid recovery system 100 includes a wayside storage system 104 coupled to the railway system. The wayside energy storage system 104 can store energy recovered from the traction power distribution network 114. In some implementations, the wayside storage system 104 can include one or more or all of an energy storage flywheel, a battery-based energy storage system (for example, a lithium-ion battery or similar battery), and a supercap-based energy storage system that can receive and store electrical energy or a combination of them. The hybrid recovery system 100 also includes a controller 106 coupled to the traction power distribution network 114, the wayside energy transmission system 102 and to the wayside energy storage system 104. The controller 106 can receive positional information 112 about a rail vehicle on the traction power distribution network 114, and transfer at least a portion of energy recovered from the rail vehicle to either the wayside energy transmission system 102 for transmission to the utility electrical grid 116 or to the wayside storage system 104 for storage based, in part, on the positional information 112 about the rail vehicle. As described above, energy recovered from the rail vehicle can include braking energy.

[0022] The controller 106 can store the positional information about the rail vehicle. The positional information can include a schedule of the rail vehicle (for example, the metro schedule), an occupancy of the rail vehicle at different times, acceleration and braking history of the cars of the rail vehicle at different times, and the rail vehicle electricity billing schedule (for example, billing rates based on peak power, time of day, demand, different grid line rates, to name a few). The controller 106 can transfer at least a portion of the energy recovered from the rail vehicle to either the wayside energy transmission system 102 or to the wayside storage system 104 based on additional information associated with the utility electrical grid 116, for example, the power rates associated with the utility electrical grid 116 and any voltage regulation schedule.

[0023] To determine the portion of recovered energy to be transmitted to the wayside energy transmission system 102 or to the wayside energy storage system 104, the controller 106 can receive power information (for example, voltage, current, or other power information) from different positions in the wayside energy recovery system 100, such as those identified in the table below:

[0024] The controller 106 can include a memory, for example, a computer- readable memory, that can store preset voltage thresholds that trigger a storage or a recuperation event - V _ps (preset(storage model)) which is the rising DC traction bus voltage level at which the energy storage is activated; Vpr (Preset(recuperation model)) which is the rising DC traction bus voltage level at which the inverter is activated; Vat (Preset(grid voltage level)) which is the decision point for the system on the AC grid voltage. In general, the storage activation threshold is lower than the recuperation activation threshold.

[0025] The hybrid system 100 includes a wayside energy transmission controller 108 operatively coupled to the wayside energy transmission system 102 and to the controller 106. The wayside energy transmission controller 108 can receive, from the controller 110, an instruction specifying the portion of the recovered energy to be transmitted to the utility electrical grid 116, and control the wayside energy transmission system 102 to transmit the specified portion to the utility electrical grid 116. The hybrid system 100 also includes a wayside energy storage controller 110 operatively coupled to the wayside energy storage system 104 and to the controller 106. The wayside energy storage controller 110 can receive, from the controller 106, an instruction specifying the portion of the recovered energy to be stored, and control the wayside energy transmission system 104 to store the specified portion of the recovered energy.

[0026] In some implementations, the controller 106 can execute two energy absorption modes. In particular, the controller 106 can execute a direct storage mode when V2 > V _ps , A2=0 and Vl>V _a t. In this mode, the controller 106 can instruct the wayside energy storage controller 110 to absorb recovered energy from the DC bus and move the energy to be stored in the wayside energy storage system 104.

[0027] Also, the controller 106 can execute an energy recuperation mode when V2>V _P s, A2=0 and VKVat. In this mode, the controller 106 can instruct the wayside energy transmission controller 108 to absorb the recovered energy from the DC bus and directly transfer the energy to the utility electrical grid 116 as power.

[0028] In some implementations, the controller 106 can execute multiple energy transfer modes. In particular, the controller 106 can execute a traction power support mode in which the controller 106 causes the wayside energy storage controller 110 to transfer energy stored by the wayside energy storage system 104 to the DC traction bus, for example, when the rail vehicle is accelerating and drawing power from the traction rectifiers. In this mode, A2>0 and the wayside energy storage system 104 has stored energy available for the transfer.

[0029] In addition, the controller 106 can execute a peak power shaving mode in which the controller 106 can cause the wayside energy storage system 104 to transfer stored energy to the rail AC system by a command from the rail vehicle's SCADA to shave the peak energy consumption. In some instances, the controller 106 can execute this mode by a combination of several wayside energy storage systems across the rail line so that the power can be transferred to offset the peak current demand at any particular location along the line.

[0030] Also, the controller 106 can execute an auxiliary support mode in which the hybrid system 100 can absorb from the DC bus in spurts when the trains are decelerating, but transfer the energy to the low voltage (380 V - 480 V) bus in a steady regulated manner so that the power consumed by auxiliary systems like escalators and HVAC systems can be offset. The controller 106 can also execute in a voltage stabilization mode in which the hybrid system 100 can transfer energy to the grid AC side or the traction DC side during periods of voltage sag independent of train acceleration.

[0031] In some implementations, the hybrid system 100 can include a grid storage system 120 coupled to the traction power distribution network 1 14 and to the grid 1 16. The grid storage system 120 can further be coupled to and operated by the controller 106. Like the wayside storage system 104, the grid storage system 120 can include one or more or all of an energy storage flywheel, a battery -based energy storage system (for example, a lithium-ion battery or similar battery), and a supercap- based energy storage system that can receive and store electrical energy or a combination of them. The capacity of the grid storage system 120 can be higher than that of the wayside storage system 104. For example, the capacity of the wayside storage system 104 can be measured in kilowatt, seconds (kWs) whereas that of the grid storage system 120 can be measured in kilowatt.hours (kWH).

[0032] As described above, the controller 106 can receive positional information 1 12 about a rail vehicle on the traction power distribution network 114, and under some circumstances, transfer at least a portion of energy recovered from the rail vehicle to the wayside energy transmission system 102 for transmission to the utility electrical grid 116 instead of to the wayside storage system 104. In some implementations, the controller 106 can transfer all or portions of the energy recovered from the rail vehicle to the grid storage system 120 instead of the grid 1 16. For example, during peak hours, which are the times of highest electricity usage over the course of the day, the controller 106 can transfer the energy to the grid 1 16. During off peak hours, the controller 106 can transfer the energy to the grid storage system 120. In another example, the controller 106 can transfer energy from the grid 1 16 to the grid storage system 120, for example, during off peak hours. In this manner, the grid storage system 120 can receive and store energy recovered from the rail vehicle. As described below, the wayside storage system 104 can be charged using energy either from the grid 1 16 or from the grid storage system 120 or from both sources.

[0033] Electricity bills often include both energy usage (kWh) charges and peak demand (kW) charges. Energy usage charges are based on the total kWh used by the rail operator for the entire month. Energy usage rates are often tiered based on time of day with the highest rates being paid at midday and lowest rates being paid at midnight. Peak demand charges are based on the maximum kW and is often calculated in 15 minute averages. Some rail operators only pay energy usage, but most pay both. The controller 106 is configured to minimize the electricity bill for the rail operator using the grid 1 16, wayside energy storage 104, and grid storage 120 as alternative sources for the energy needed by the train.

[0034] In some implementations, the controller 106 can be configured to operate in three modes of operation: energy savings mode, peak shaving mode, and hybrid mode.

[0035] Rail operators are often credited by the utility for providing energy (kWh) to the grid 1 16 via something like the wayside energy transmission controller 108. These credits are often complex with higher rates being paid during peak hours and lower rates or no credits being paid during off-peak hours. Utilities also prefer more constant energy to the utility. So, the spikes in energy from a rail vehicle coming into a station may not be valuable to them. [0036] When a rail vehicle comes into a substation, the controller 106 can determine how much energy should be stored into the wayside energy storage system 104 and how much should be generated back to the grid 1 16 through the wayside energy transmission controller 108. It will likely only put as much energy back to the grid as the utility will pay for and put all the remaining energy to the wayside energy storage system 104.

[0037] It is not likely that the grid storage system 120 will be charged by a rail vehicle through the wayside energy transmission controller 108 because it would be more valuable to get the energy (kWh) credit from the utility than it would be fill the grid storage system 120. The grid storage system 120 will most likely be filled at night when energy usage rates are low.

[0038] The main value of the grid storage flywheel 120 would be in peak shaving mode which attempts to minimize the demand (kW) charges from the utility. The demand (kW) charges can comprise a large part of the electricity bill from the utility. When this is the case, the most cost savings can be realized by limiting the maximum demand (kW) required from the grid. When a rail vehicle takes off, it requires a lot of power (kW) and then as it accelerates, that power falls off. So, the controller 106 could be programmed in such a way as to limit the power (kW) that it pulls from the grid. The remaining demand would then be pulled from both the wayside energy storage system 104 and, as necessary, the grid storage system 120. Because the wayside energy storage system is only being filled when the rail vehicle arrives at the substation, it will not likely have enough energy (kWh) or power (kW) to power the train as it accelerates away from the substation.

[0039] It may also be beneficial when in peak shaving mode to trickle charge the wayside energy storage system either from the grid 1 16 or from the grid energy storage system 120. By keeping the wayside energy system full, the demand (kW) from the grid which is what the utility charges for can be minimized.

[0040] In sum, the hybrid system 100 described here can combine a compact storage element with a dual inverter grid tie technology that can sense the electrical power system automatically and support multiple modes. In addition, with built-in intelligence, the system can direct the saved energy dynamically to optimize the system for the best payback in terms of avoided costs or leveraged operation. Depending upon the operation mode and sensed conditions, the controller 106 described above can transfer all of the recovered energy to the wayside storage system 104 or to wayside transmission system 102. For example, when a rail vehicle decelerates into a substation, the controller 106 can determine how much of the available free energy from the deceleration can be allocated to the wayside storage system 104 and how much can be allocated to the grid 1 16 through the wayside energy transmission controller 108. In some instances, the controller 106 can allocate some energy to the grid storage system 120. Conversely, when the rail accelerates away from the substation, the controller 106 can decide the most cost effective sources for the energy needed for the acceleration. The controller 106 can use the energy from the wayside energy storage system 104 or from the grid 116 or a combination of them based on factors including the time of day and peak power consumed.

[0041] FIG. 2 is a flowchart of an example process 200 of providing power to a wayside storage system of the hybrid wayside energy recovery system. In some implementations, the process 200 can be implemented by the controller 106 or a similar controller.

[0042] At 202, it is determined that the wayside energy storage system 104 requires power. For example, the wayside storage system 104 may have released some of the stored energy, for example, to operate the rail vehicle or for other reasons. In energy savings mode, the wayside storage system 104 will remain empty most of the time, charge when a train arrives, and discharge either to the train when it leaves the substation or back to the grid through the wayside energy transmission controller 108 if the utility will pay higher rates than they charge which is often the case in subsidized markets. In peak shaving mode, the wayside storage system 104 will remain full most of the time, trickle charging from the grid as needed so it has as much energy as possible to support the train when it leaves the substation. In hybrid mode, the wayside storage system 104 may be kept partially full so it can either charge or discharge energy as needed.

[0043] The controller 106 can determine that the energy stored by the wayside storage system 104 has dropped below a threshold energy value necessitating that the wayside storage system 104 be recharged. The required power can be drawn either from the grid 1 16 or from the grid storage system 120. As described above, the act of storing energy recovered from the traction power distribution network 114 in the grid storage system 120 is associated with a cost. Also, the cost of drawing energy from the grid 1 16 is associated with a cost. At times, it may be more cost-efficient to draw energy from the grid 1 16 than from the grid storage system 120, or vice versa. In some implementations, the controller 106 can compare the costs to determine which source is more cost-efficient. The controller 106 can implement the cost determination in any order, for example, sequentially, simultaneously.

[0044] At 204, the cost of drawing power from the grid 116 is compared to the cost of drawing power from the grid storage system 120. To compare the costs, the controller 106 can determine the cost to draw power from the grid storage system 104. The controller 106 can also determine the cost to draw power from the grid 1 16. The cost to draw power from the grid 1 16 is dependent, among other factors, on the time of day. That is, at peak hours, which are the times of highest electricity usage over the course of the day, the cost to draw power from the grid 1 16 is higher compared to off- peak hours. The cost is also dependent on a quantity of power consumed. For example, the cost of power consumed up to a first threshold power value can be different from the cost of power consumed beyond the first threshold power value. The controller 106 can determine the cost to draw power from the grid 1 16 based on these and other factors.

[0045] For example, at noon, the utility may charge $0.45/kWh for a tiered "time of use" plan. It may only charge $0.10/kWh at midnight. The same utility may pay $0.60/kWh for energy put back to the grid at noon and pay $0.00 for energy put back to the grid at midnight. In this case, at noon, when a rail vehicle brakes and decelerates toward a substation, it puts energy back on the traction power distribution network 114. The controller 106 would then put most if not all of that energy back to the grid through the wayside energy transmission controller 108 because this will save more money than storing the energy in wayside energy storage system and using that stored (free) energy to re-accelerate the rail vehicle away from the substation. At midnight, the controller 106 would instead store the energy in the wayside energy storage system and use that free stored energy to re-accelerate the rail vehicle away from the substation because it would not make any money by putting that energy to the grid. [0046] At 206, a determination is made if power should be drawn from the grid or from the grid storage system 120 based on a result of comparing the costs as described above. If the controller 106 determines that drawing power from the grid 116 is more cost-efficient, then at 208, power is transmitted from the grid 116 to the wayside storage system 104. Alternatively, if the controller 106 determines that drawing power from the grid storage system 120 is more cost-efficient, then at 210, power is transmitted from the grid storage system 120 to the wayside storage system 104. In some implementations, the controller 106 can determine to recharge the wayside storage system 104 using power drawn from both the grid 1 16 and the grid storage system 120 based, for example, on an optimization of the time to recharge the wayside storage system 104 and the cost to draw power from both the grid 116 and the grid storage system 120.

[0047] Certain implementations have been described above in the context of a rail vehicle. In some implementations, the controller 106 can be configured to make similar decisions in the context of multiple rail vehicles. Also, multiple hybrid wayside energy systems, similar to the one described above, can be implemented at different locations in the railway system.

[0048] Thus, particular implementations of the subject matter have been described. Other implementations are within the scope of the following claims.