Patent Application
20160190801
The current disclosure relates to systems and methods for scalable energy storage. In particular, the current disclosure relates to reducing the sensitivity of scalable energy storage systems to battery health.
An energy storage system typically includes a plurality of batteries or other energy storage devices coupled together to provide electric power for an application. The total energy of the system may be scaled up or down by increasing or decreasing the number of batteries of the system. Energy storage systems may be used in any mobile or stationary application (providing power to electric vehicles, buildings, machines, etc.). In some applications, an energy storage system may be coupled to an electrically powered installation connected to the local electric grid. Such energy storage systems may sometimes be referred to as grid energy storage systems or stationary energy storage systems. In such an application, electric power from the grid may be used to charge the batteries of the energy storage system when supply exceeds demand (corresponding to a lower energy cost period). This stored energy may then be used to provide (or supplement) power to the installation when demand exceeds supply.
The plurality of batteries of the energy storage system are connected to the electric grid through an inverter. The inverter converts AC current to DC current and vice versa. During a charge cycle of the energy storage system, AC current from the grid is converted to DC current by the inverter and directed to the batteries of the energy storage system. The energy storage system may also include a discharge cycle where DC current from the energy storage system is converted to AC current by the inverter and directed to the grid. In conventional energy storage systems a plurality of batteries may be connected together to a single large inverter. In such systems, the single inverter may convert the DC current from all the batteries to AC current. In such configurations, the electrical performance (for e.g., power output) of the grid storage unit may be limited by the weakest battery of the plurality of batteries. The current disclosure overcomes this or other deficiencies of conventional energy storage systems.
Embodiments of the present disclosure relate to, among other things, grid energy storage systems and methods. Each of the embodiments disclosed herein may include one or more of the features described in connection with any of the other disclosed embodiments.
In one embodiment, a scalable energy storage system is disclosed. The energy storage system may comprise a plurality of battery packs including at least a first battery pack and a second battery pack. The system may also include a plurality of inverters. The plurality of inverters may include at least a first inverter and a second inverter. The plurality of battery packs may be electrically coupled to the plurality of inverters such that the first battery pack is individually connected to an input of the first inverter and the second battery pack is individually connected to an input of the second inverter.
In another embodiment, a scalable energy storage system is disclosed. The scalable energy storage system may include a plurality of battery packs and a plurality of inverters. Each battery pack of the plurality of battery packs may be electrically connected to a separate inverter of the plurality of inverters
In yet another embodiment, a method of making a scalable energy storage system is disclosed. The method may include electrically connecting a plurality of battery packs to a plurality of inverters such that each battery pack of the plurality of battery packs is electrically connected to an input of a separate inverter of the plurality of inverters. The method may also include electrically connecting together an output of each inverter of the plurality of inverters.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the present disclosure and together with the description, serve to explain the principles of the disclosure.
The present disclosure describes an energy storage system associated with an electric vehicle charging station. While principles of the current disclosure are described with reference to a charging station, it should be understood that the disclosure is not limited thereto. Rather, the disclosed energy storage systems and methods may be used in any application.
In the prior art energy storage system 10, each battery of the plurality of battery packs 50 are similar (in terms of chemistry, number of cells, battery health, etc.) to each other. If one of the batteries is weaker than the others (for e.g., lower amount of charge capacity, etc.), the output parameters (power, voltage, current, etc.) of the energy storage system 10 may be limited by the weakest battery. That is, rather than discharging equally, energy will be preferentially discharged from a weaker battery than the healthier batteries of the plurality of batteries 50. This preferential discharge from a weaker battery is the result of impedance changes that occur in a battery with age. Therefore, when scaling up the energy storage system 10 by adding more batteries to the plurality of batteries 50, care must be taken to add batteries that are similar to the existing batteries (of the plurality of batteries 50). This need of finding similar batteries may limit the available options and increase cost because lower cost used batteries from other applications (for e.g., refurbished batteries and used batteries from electric vehicles, etc.) may not be an option.
During the discharge cycle, power from the plurality of battery packs 150i flow towards the charging station 30 (as indicated by the solid line arrows), and during the charge cycle, power from the electric line 22 flows towards the plurality of battery packs 150i (as indicated by the dashed-line arrows). The power from the plurality of battery packs 150 may be used to charge vehicles at the charging station 30. During the discharge cycle, each inverter 160i converts the DC current from its connected battery pack 150, to AC current, and during the charge cycle, each inverter 160i converts AC current from the grid 20 to DC current to charge its connected battery pack 150i.
Controller 70 may activate and control the charge and discharge cycle of the energy storage system 140. Controller 70 may include memory and logic devices configured to store data and perform arithmetic operations on the data. For example, based on a tariff schedule (table of energy cost at different times) or other variables, the controller 70 may activate the charge and discharge cycle of the energy storage system 140. In some exemplary embodiments, the energy storage system 140 may be charged during times of low energy cost and discharged during times of high energy cost. In some embodiments, during times of high energy cost, the charging station 30 may operate entirely using the power from the energy storage system 140. Alternatively, at such times of high energy cost, a portion of the power (e.g., 50%) may be provided by the electric grid 20 and the remaining portion (i.e., 50%) may be provided by the energy storage system 140.
In some embodiments, each battery pack 150; (i=1−n) of the plurality of battery packs 150 may include one or more batteries electrically connected together in series or parallel. In some embodiments, a battery pack 150i may include several (10, 9, 8, 7, 6, 5, 4 etc.) batteries connected together in series. In other embodiments, a battery pack 150i may only include one battery. A battery pack 150i may include one or more batteries with multiple cells. These multiple cells may be electrically connected together in series or parallel. In some embodiments, some cells of a battery may be connected in series while other cells may be connected in parallel. The cells of a battery may be of any construction (for e.g., cylindrical cell, prismatic cell, button cell, pouch cell construction, etc.).
The batteries of a battery pack 150i may include any type of batteries known in the art. In general, these batteries may have any chemistry. For instance, these batteries may include, among others, lead-acid batteries, Nickel Cadmium (NiCad) batteries, nickel metal hydride batteries, lithium ion batteries (e.g., lithium titanate), Li-ion polymer batteries, zinc-air batteries molten salt batteries, etc. Some of the possible battery chemistries and arrangements are described in commonly assigned U.S. Pat. No. 8,453,773, which is incorporated herein by reference in its entirety.
Each battery pack 150i of the plurality of battery packs 150 may have a State of Charge (SOC) and a State of Health (SOH). The SOC of a battery is the amount of electric charge contained in the battery. Conceptually, SOC is equivalent to the level of a fuel in the fuel tank of a vehicle. A battery with full charge is considered to have 100% SOC, and a completely drained battery is considered to have 0% SOC. The SOH of a battery is a parameter that reflects the general condition of the battery and its ability to provide power compared with a fresh battery. Conceptually, SOH is equivalent to the size of the fuel tank of a vehicle. During the lifetime of a battery, its SOH (also referred to as health) and performance tends to deteriorate gradually due to age until eventually the battery is no longer usable. This is conceptually similar to the size of a fuel tank reducing with age (due to deposits, etc.). The SOH is an indication of the point in the life of a battery and a measure of its condition (relative to a fresh battery). A battery is considered to have 100% SOH when new and 0% SOH at end of life.
As illustrated in
Although not a requirement, in some cases, each inverter 160, may have substantially the same power capability as the battery pack 150i it is associated with (i.e., inverter 160i is paired with its associated battery pack 150i). In this disclosure, the terms substantially and about are used to indicate a possible variation of 10%. For example, in an embodiment where battery pack 1501 has a power of 100 KW and battery pack 1502 has a power of 150 KW, inverter 1601 may have a power capability of 100 KW and inverter 1602 may have a power capability of 150 KW. However, this is not a requirement since using an inverter 160i of a larger capacity than its associated battery pack 150i merely under-utilizes the inverter 160i and using an inverter 160i of a lower capacity than its associated battery pack 150i merely makes power conversion slower.
Each battery pack 150i may be of the same or different type (chemistry, number of batteries, cells, etc.) than other battery packs 150i of the plurality of battery packs 150. Each battery pack 150i may also have the same or different SOH and SOC than other battery packs 150i of the plurality of battery packs 150. In some embodiments, some of the battery packs 150i may include only one battery while other battery packs 150i may include multiple batteries. In some embodiments, some of the battery packs 150i may be lithium titanate battery packs with eight batteries connected in series with each battery having ten cells connected in series, while others may have another chemistry (for example, lead-acid, nickel cadmium, nickel metal hydride, lithium ion, zinc air, etc.) and a different number of batteries and/or cells. In an exemplary embodiment, some of the battery packs 150i may be 2 year old battery packs from a Chevrolet Volt electric car, while some battery packs 150i may be new battery packs from Tesla and/or Nissan Leaf electric cars, and the remaining battery packs 150i may be refurbished 5 year old battery packs from Proterra electric buses.
Unlike prior art energy storage system 10 of
Although energy storage system 140 is illustrated as having an equal number of battery packs 150i and inverters 160i, this is not a requirement.
Similar to energy storage system 140 of
It should be noted that although battery packs and inverters are illustrated as being separate parts in
In contrast with prior art energy storage systems, energy storage systems 140 and 240 may be assembled (and scaled up) using battery packs of different types and health. The ability to combine dissimilar batteries used in different applications (e.g., batteries used previously in computer applications with batteries used previously in vehicle applications) in an energy storage system has the potential of substantially reducing the cost of the energy storage system.
For example, if a plurality of batteries were used together as a module in a desktop computer UPS, an inverter sized (e.g., paired) to handle that module can be used form a first battery-inverter pair. This first pair can then be combined with a battery (or batteries) that was used in another application (different computer systems or in a completely different application) to form an energy storage system. If the battery is a battery pack used in a Toyota Prius, an inverter can be paired with this battery pack to form a second battery-inverter pair. This second battery-inverter pair may then be combined with the first battery-inverter pair to form the energy storage system. If 8 battery packs spent their lives together in an electric bus, an inverter can be sized to match the output of the 8 packs together to form a third battery-inverter pair. This third battery-inverter pair may then be combined with the first and second battery-inverter pairs to form the energy storage system. An advantage in all of these cases is that the lowest common denominator for sizing the inverter is the maximum number of batteries used together with a common history in a prior application. Batteries in battery packs having entirely different histories may be uniform in age within themselves. These previously used battery packs can be now used together in one energy storage system in a “second life” application without being constrained by the histories of other battery packs in that system.
In prior art energy storage systems, a plurality of batteries are connected in parallel to a conductor connected to an inverter (i.e., in the prior art, the outputs of the batteries are paralleled to an inverter). In an energy storage system of the current disclosure, the output of each battery (or group of batteries) is connected to an inverter and the outputs of the inverters are then paralleled. Paralleling the outputs of the inverters is much more effective in terms of the ability to combine different battery technologies (different SOHs, SOCs, chemistries, etc.) than paralleling the outputs of the batteries themselves (as in the prior art). Batteries can only be paralleled if they are perfectly matched. Else, the combined system will experience a range of issues due to impedance differences and voltage differences amongst the batteries. “Second life” battery usage is a huge opportunity to extract more value out of battery systems that are past the defined end of life in a weight sensitive application such as automotive vehicle. The systems and methods of the current disclosure enables and/or simplifies the utilization of second life batteries in larger grid tied systems.
While principles of the present disclosure are described with reference to an energy storage system associated with a vehicle charger, it should be understood that the disclosure is not limited thereto. Rather, the systems and methods described herein may be employed in an energy storage system used in any application. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, embodiments, and substitution of equivalents all fall within the scope of the embodiments described herein. Accordingly, the invention is not to be considered as limited by the foregoing description. For example, while certain features have been described in connection with various embodiments, it is to be understood that any feature described in conjunction with any embodiment disclosed herein may be used with any other embodiment disclosed herein.
