Patent Application
20160190867
This invention relates to the area of hybrid energy storage systems using at least two or more energy storage and/or supply approaches as an alternate way to provide energy when an outage occurs under the supervision of a master integrated control that determines when to trigger the different systems. More particularly, this invention refers to creating low-cost solutions to provide uninterrupted and sustained energy supply during the occurrence of outages to critical locations such as data centers, hospitals, telecommunications stations, emergency communication facilities, laboratories, manufactures of critical production products or equipment, military bases, certain government facilities, and others less critical but with a desired power quality supply such as residential homes and office buildings. Some of the energy storage approaches considered as alternate ways to supply energy to critical loads when outages occur include compressed air or other fluid energy storage, battery banks, super-capacitors, induction energy storage, fuel cell banks, and flywheel energy storage.
Backup power systems that consist in only batteries or batteries combined with a later transition to unreliable diesel systems (arranged in parallel to increase reliability) are the norm for data centers, telecommunications stations, hospitals, and others. Even though battery performance continues to improve over time, the cost of battery systems remains high, with the most expensive batteries, the lithium ion ones, achieving durations in the order of 2000 cycles or more, the less expensive lead acid batteries with durations in the order of 200 cycles. In addition, they require a great control of ambient temperature besides a rigorous maintenance and monitoring. As a consequence, battery systems have to be replaced every two to five years, depending on the battery technology and usage. On the other hand, air-compressed systems have been used in power systems to store energy during off peak hours to increase the efficiency of combustion engines during peak energy-demand.
The limitation of pure air-compressed energy storage systems have been the low efficiency of the compression and decompression (see Rice and Li “Optimal Efficiency-Power Tradeoff for an Air Motor/Compressor With Volume Varying Heat Transfer Capability” Dynamic Systems and Control Conference and Bath, USA, pp. 145-152, 2011). More recently, the efficiency of pure air compressed systems has been increased to almost 60% maintaining an adiabatic process (see Rufer and Lemofouet “Energetic Performance of a Hybrid Energy Storage System based on Compressed Air and Super Capacitors” published in the Symposium on Power Electronics, Electrical Drives, Automation & Motion, Italy, May 2006, also Dein Shaw, Jyun-jhe Yu, and Cheng Chieh “Design of a Hydraulic Motor System Driven by Compressed Air” Energies, 2013, vol. 6, issue 7, pages 3149-3166, and U.S. Pat. No. 8,117,842 and No. 8,234,868). The heat released during compression is fed back to the system during expansion. Other proposed solution to increase efficiency has been combining air and hydraulic fluids. In parallel, more efficient air motors have been developed for automobiles (see U.S. Pat. No. 6,868,822). But even though these motors claim efficiency greater than 90%, the deployment to the field is limited due to the low energy density typically achievable with air compression; yielding low-range vehicles. For the reasons explained above, we proposed an application that takes the advantages of air-compressed systems and minimizes the disadvantages
An example of a hybrid energy storage system that does not optimizes for extended operational life can be seen in U.S. Pat. No. 8,754,547.
Uninterruptible backup energy systems have the main goal to keep seamless operation of the equipment attached to the backup storage system during power outages. In order to achieve this, traditional systems are based on a DC-link capacitor, a large battery bank, and possibly a group of diesel and gas generators. The key to uninterrupted energy supply is in the response time of the different parts of the backup system. The response time of the capacitors is in the order of nanoseconds or microseconds and they are the insurance of the interruptible power system supply, follow by the batteries that have a response time in the order of milliseconds. For longer backup supply duration, energy backup systems use traditional AC diesel generators that are in standby mode in the backup system and have response times in the order of many seconds to minutes. The diesel generator needs to wait the proper speed to create the 60 (or 50 Hz) needed in power systems. In this invention, an ultrafast or fast, previously charged air-based energy backup system is attached to the DC-link. The startup of this system is designed to be a constant time of about a couple of seconds. This system accomplishes two main functions. It reduces the amount of batteries required and greatly decreases the energy demand and stress on the used batteries; this is achieved thanks to the addition of the air-based backup system that begins reliable operation after about a couple seconds of the outage.
The key factor to accomplish a short startup time for the air-based backup system is to use discrete sets of air-based/energy-generator units that operate at a few kilowatts each. The number of these units is scalable to satisfy the total power required in the specific application. These small pneumatic-motor/electrical generator units have intrinsically small momentum of inertia and as a consequence produce a fast startup time compared to a larger single unit designed to provide the whole power required.
Using the hybrid approach described, the battery bank can be minimized up to 80% of the typical full battery design and the battery energy deep cycles required can be reduced, therefore extending their life. This patent proposes the full control and interaction of the system taking into account the paradigm that the faster energy providers are the capacitors, with time constants close to nanoseconds, followed by the batteries with time constants of milliseconds, and lastly the air-compressed energy generation with time constants of one or two seconds. They are ten to one hundred times faster than diesel or gas generators.
This has the advantage that the number of back-up diesel generators can be reduced because the reliability and availability of air-compressed generators are considerably greater than that of combustion-based generators. The energy density of compressed air at low pressure is not high and possesses restrictions because numerous and large-volume tanks are needed for energy storage. This can be mitigated because these tanks can be placed outdoors, allowing the ability to pile large amounts of exterior storage tanks. High air pressure systems can be used as an alternative when space is limited or when viability cost analyses suggest their usage.
New trends of energy backup systems based on air try to maximize the efficiency in a reversible adiabatic process. In this invention, while efficiency is important, it is not the main point. The crucial aspect is a very fast startup activation of the air-generator units to optimize the battery life and dimensioning. Therefore the process of energy charging (air compression) and energy generation is separated in two stages conducted by the compression system and the air-based electricity generation system. The latter is discretized in small air-based/energy-generator units for fast response time.
It depicts the hybrid energy backup system 100. It is composed of (1) a battery bank 120 that includes the batteries 122 and one or more power converters 124 that allow connection to the DC link, (2) DC-link capacitors 160, (3) the air-based energy backup system 200 that comprises (a) the energy charging and storage system 240 and the energy release system 280. The energy charging and storage system is composed of one or more compressor motors 241, one or more air compressors 242, one or more gas storage tanks 244, one input valve per gas storage tank 243. The energy release system 280 consists of one or more pneumatic motors 282, one or more pressure regulators 283, one or more output valves from the tanks 285, one or more electrical generators 287, and one or more power converters 284, and (4) an integrated system master controller 300 that senses the grid status through the sensing unit 400.
The master controller 300 is the heart of the system in charge of controlling the main two phases of operation. The operation phases are: (1) energy charging and standby-sensing mode; (3) backup energy generation.
Energy Charging
During this phase, the tanks are charged with compressed air. The energy charging occurs right after the system is installed. Using external available energy the master controller 300 and the motor(s) 241 in
If an outage occurs, the backup energy generation phase immediately triggers to provide uninterrupted electricity to the desired facilities or equipment that are appropriately connected to the UPS (power converter) 180. The UPS acts using first the energy stored in the capacitors, very shortly after, the battery bank starts operation with simultaneous turned on of the tank release valve. The air flows from the tank(s) to the pneumatic motor(s) whose movement activates the generator motor(s) in around two seconds. The power converters receive the electrical energy from the generator and supply it to the DC link. As the air-based backup system releases its stored energy, the master controller decreases the demand on the battery bank accordingly until the battery bank is not providing anymore energy; this process takes a few seconds.
The proposed system is scalable at the energy generation and storage phase, also the ratio of different source of energy storage can be modified. This allows to discretely adjust the amount of energy stored and also to adjust the amount of energy delivered.
| Number | Date | Country | |
|---|---|---|---|
| 62097236 | Dec 2014 | US |
