Patent Application
20120059527
The present invention generally relates to energy management. More particularly, it relates to a distributed energy storage system, and applications thereof.
Electricity and the power networks used to transmit and distribute it are vital. Deregulation and shifting power flows, however, are forcing the power network to operate in ways it was never intended. In the United States, for example, the number of desired power transactions that cannot be implemented due to transmission bottlenecks continues to increase each year. This trend, along with a trend of increased electric power demand, has pushed the capacity of many transmission lines to their design limits. In some regions, the increase in electric power demand is such that periods of peak demand are dangerously close to exceeding the maximum supply levels that the electrical power industry can generate and transmit.
What are needed are new systems, methods, and apparatuses that allow the power network to be operated in a more cost effective and reliable manner.
The present invention provides a distributed energy storage system, and applications thereof. In an embodiment, the distributed energy storage system includes power units, wherein each power unit has a multi-cell battery; a battery manager that monitors battery cell voltages and temperatures; and a controller. The controller provides a first control signal that causes the power unit to store energy in the battery and a second control signal that causes the power unit to generate an alternating current. A server in communication with each of the power units stores data collected from the power units about the batteries and analyzes the data to determine how much available energy is stored in the batteries that can be used to alter a load demand of a power network. In an embodiment, the batteries are lithium ion batteries capable of storing at least ten kilowatt-hours of energy. In an embodiment, each power unit is coupled to a solar energy power source that is used to charge the power unit battery.
It is a feature of the distributed energy storage system of the present invention that it can be used to shift a utility's electrical power demand in time and thus present opportunities to reduce the cost paid for peak load power as well as reduce transmission congestion.
Further embodiments, features, and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.
The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention.
The present invention is described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit or digits in the corresponding reference number.
The present invention provides a distributed energy storage system, and applications thereof. In the detailed description of the invention herein, references to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.
The present invention provides a distributed energy storage system, and applications thereof. In an embodiment, the distributed energy storage system includes power units, wherein each power unit has a multi-cell battery; a battery manager that monitors battery cell voltages and temperatures; and a controller. The controller provides a first control signal that causes the power unit to store energy in the battery and a second control signal that causes the power unit to generate an alternating current. A server in communication with each of the power units stores data collected from the power units about the batteries and analyzes the data to determine how much available energy is stored in the batteries that can be used to alter a load demand of a power network. In an embodiment, the batteries are lithium ion batteries capable of storing at least ten kilowatt-hours of energy. In an embodiment, each power unit is coupled to a solar energy power source that is used to charge the power unit battery.
Battery 402 can be any type of battery suitable for multiple charging and discharging cycles. In embodiments, battery 402 is preferably sized to supply 10 to 15 kilowatt-hours of electrical energy with a life expectancy of 3000 to 4000 charge and discharge cycles. Suitable batteries include, for example, the Thunder Sky lithium-ion batteries, which are available from Thunder Sky Energy Group Limited, whose address is Thunder Sky Industrial Base, No. 3 Industrial Zone, Lisonglang Village, Gongming Town, Bao'an District, Shenzhen, P.R.C, 5181016 (see http://www.thunder-sky.com). Other batteries are also suitable and can be used.
DC electrical bus 404 electrically couples battery 402 to charger/AC-to-DC converter(s) 410 and to inverter/DC-to-AC converter(s) 412. In embodiments, the charger and the inverter may be combined in a single charger-inverter unit, for example, to reduce costs. In a charger-inverter unit, the same power electronics can be used for both charging battery 402 and for generating an alternating current from the energy stored in battery 402. In an embodiment, DC electrical bus 404 is used to supply power to optional DC loads. DC electrical bus 404 can also be used to couple battery 402 to a source of DC power that is used to charge battery 402.
Battery manager 406 monitors the cells of battery 402 and prevents the cells from being over-charged and over-discharged. In embodiments, as described in detail below, battery manager 406 balances the cells of battery 402 and operates the cells of battery 402 in a manner that makes battery 402 have an extended lifetime. In embodiments, battery manager 406 monitors the voltage and temperature of each battery cell of battery 406 and the current of battery 406. These monitored parameters are used by battery manager 406 to control the state of charge and the state of health of battery 406.
Controller 408 controls the operation of power unit 116. As shown in
Charger/AC-to-DC converter(s) 410 receives AC power from AC electrical bus 414 and converts this power to DC power that is used to charge battery 404. The sizing of charger/AC-to-DC converter(s) 410 is dependent on the energy storage capacity of battery 402. In an embodiment, charger/AC-to-DC converter(s) 410 is selected so that battery 402 can be charged at a rate of about 0.3 C. In other embodiments, a larger charging rate may be desirable and so charger/AC-to-DC converter(s) 410 should be sized accordingly. The operation of charger/AC-to-DC converter(s) 410 is controlled by controller 408. In an embodiment, information about the state of charger/AC-to-DC converter(s) 410 is provided to controller 408 and transmitted to a remote location by transceiver 416.
Inverter/DC-to-AC converter(s) 412 receives DC power from battery 402 and DC electrical bus 404 and converts this power to AC power that is supplied to AC electrical bus 414. The sizing of inverter/DC-to-AC converter(s) 412 is dependent on the energy storage capacity of battery 402. In an embodiment, inverter/DC-to-AC converter(s) 412 is selected so that the useful energy stored in a charged battery 402 can be supplied at a rate of about 0.3 C or during a period of about three hours. In other embodiments, a larger discharge rate may be desirable and so inverter/DC-to-AC converter(s) 412 should be sized accordingly. The operation of inverter/DC-to-AC converter(s) 412 is controlled by controller 408. In an embodiment, information about the state of inverter/DC-to-AC converter(s) 412 is provided to controller 408 and transmitted to a remote location by transceiver 416. In embodiments, inverter/DC-to-AC converter(s) 412 operates as a current source/grid-tied inverter.
AC electrical bus 414 couples charger/AC-to-DC converter(s) 410 and inverter/DC-to-AC converter(s) 412 to a utility grid power source, an optional power source and/or AC loads.
Transceiver 416 is used to transfer data to and from controller 408. Transceiver 416 can be any type of transceiver. In embodiments, transceiver 416 facilitates either wired or wireless communications between a remote location and controller 408.
In an embodiment, battery manager 406 and controller 408 operate to manage the cells of battery 402 in the manner described in reference WO/2007/128876, titled “Method And Apparatus For The Management Of Battery Cells,” which is incorporated herein by reference in its entirety. As described therein, the battery manager and/or controller discover that one of the cells of battery 402 has a capacity higher than others during a charging or discharging process. Instead of just stopping the charging process as the weakest cell becomes fully charged, the most powerful cell is for example charged slightly more than the others. The result is that the most powerful cell sustains slight damage and its capacity decreases closer to other cells. The discharging process is indeed stopped whenever the voltage of even a single cell decreases too much, which means that in practice the discharge must always be stopped as determined by the cell of the lowest state of charge. However, this feature is counteracted by anticipation, wherein the weakest cell is supplied with some “virtual capacity” from all slightly more powerful cells, causing the weaker cell to discharge more slowly than the other cells. For example the charging can be made with 1% of the discharging current, resulting in a 99% discharge cycle as compared to other cells. The charging during the discharge cycle is lowering the stress of the cell and not actually charging the cell. The anticipation data is acquired by computing it from collected statistical data. Then, also in a subsequent discharge cycle, the weakest cell can be treated a bit more gently than the other cells, that is it is possible, for example, to transfer energy for assisting the weakest cell during the next discharge cycle by using a single cell's galvanically isolated charger (see for example
Accordingly, in a subsequent or next charge and discharge cycle, the weakest cell is stressed slightly less than the others and the discrepancy evens out. In conventional battery management practices, the weakest cell is stressed in every cycle more than the others with respect to its capacity and thereby deteriorates even more. The method used in embodiments of the present invention, however, is easing the weaker cell both during charge and discharge. However, this is not a requirement of the present invention. In embodiments of the present invention, the battery manager and/or controller operate using collected history information, and they plan in advance the needed compensating measures. Conventional battery management systems do not take into account the capacity differences of cells when managing the depth of charge-discharge cycles, and at best they typically only control battery charging and discharging on the bases of cell voltage differences.
In embodiments, the battery manager and/or controller keep records of the charge, discharge, temperature, impedance and capacity, as well as other useful information, of each cell. For example, when a given cell has been intentionally overcharged, it can be expected to still have more charge than the others at the end of a subsequent discharge cycle. However, the difference in capacity is detectable over the very next cycle in the cell behavior. Accordingly, the particular cell can be discharged as required by the cell condition along with other cells for all of those to attain empty and full charge levels at the same time. Since some of the capacity of a single cell is intentionally discarded, it is advisable to keep management algorithms quite moderate to equalize properties of the cells little by little. The ultimate changes, which have an impact on the operation of battery 402, should be equalized at a very early stage of its life cycle. However, the operation and conditioning processes of cells can be continued for as long as power unit 116 is in service.
In embodiments, battery manager 406 and/or controller 408 track and keep records of the temperature of each cell of battery 402. As would be known to persons skilled in the relevant art(s) given the description herein, cell temperature can have a considerable effect on the cell behavior. Additional details regarding battery manager 406 and controller 408, as well as their operation, are provided below.
In an embodiment, control program 504 controls the charging of battery 402 and the generation of AC power from the energy stored in battery 402. Control program 504 includes remotely programmable variables, for example, that allow a utility to control when battery 402 is charged and when AC power is produced, and thereby alter power demand for a power network such as power network 100 described above.
In an embodiment, battery monitor program 506 is responsible for implementing or assisting in the implementation of some or all of the features of the battery management functions described herein.
As shown in
As shown in
The cells 600a-n of battery 402 are monitored and controlled by control circuitry 705 of the battery cell control cards 700a-n. In an embodiment, the control circuitry 705 of each battery cell control card 700 may include an embedded central processing unit (CPU), which is in communication with controller 408. The CPUs collect information about the battery cells.
In an embodiment, during operation a galvanically isolated charger or power supply produces a direct current needed for charging the battery cells under control of controller 408 and control circuitry 705. The battery cells 600a-n are connected in series and through them passes a current from the power supply. Each battery cell control card 700 is in communication with one battery cell 600. The battery cell control cards 700a-n are linked by a communications network bus to each other and to controller 408, which enables controller 408 and control circuitry 705 to collect cell-specific information and to control management of each battery cell 600a-n. In communication with each battery cell control card 700 is a temperature sensor, a power converter, and a voltage monitor. Other instruments used for measuring cell properties can also be included. In an embodiment, the power converter acquires its current from the voltage of the entire battery 402 or directly from a power supply. The power converter is preferably galvanically isolated.
When the power converter is not connected and the system is in a discharge cycle, a charger in communication with the battery cell control cards can discharge the entire battery, if necessary, and charge an individual battery cell linked with the battery cell control cards 700. This enables, for example, providing a very high efficiency in battery equalization procedures during a discharge process. The difference between the charger and the energy derived from the cells is compensated for during a charging process by adjusting the output of the power supply. The controller and/or control circuitry executes compensatory calculations and controls the operation of all power converters.
In operation, during the course of a normal charging cycle, a regulated current and voltage for charging the cells of battery 402 is generated by a charger or power supply under the control of controller 408. The charging process is started for example by using a variable constant current and by monitoring operating parameters of the battery cells. After the voltages have risen close to the values of a fully charged cell, transition is made to an equalizing charge, as necessary. At this point, a variable current at a constant voltage is supplied by the charger or power supply, depending on the number of active power converters. Battery cell parameters are monitored by the battery cell control cards, and this information is continuously collected and sent to controller 408. The charging is controlled by controller 408 and/or control circuitry 705 in such a way that the current approaches zero after all power converters 702 have completed their charging/balancing functions.
In an embodiment, the operation of the battery cell control cards 700 is actively controlled by controller 408 to obtain a desired state of charge. Notable functions include, for example, a slight overcharge of one or more battery cells, a deep discharging of individual cells, and/or a discharge cycle proportionally higher or lower with respect to the true capacity of a cell.
In an embodiment, battery cell equalization can be performed with the power supply in operation or during a discharge cycle. By being able to charge and discharge a single battery cell in a controlled manner, battery manager 406 and controller 408 have the capability of decreasing or increasing the stress on particular battery cells during a charge, storage or discharge cycle. A cell-specific temperature measurement is performed in embodiments because the properties of a cell fluctuate as a function of temperature. Furthermore, the generation of heat provides information about the condition of a cell such as, for example, its internal series resistance. Charging a cell which is already fully charged results in the generation of a considerable heat power, which may potentially destroy the cell. Moreover, by monitoring individual battery cell temperatures, it is possible to provide a software-independent overheating protection, which overrides all other controls and opens the battery circuit.
In an embodiment, battery manager 406 and/or controller 408 can be used to measure the capacity of each battery cell accurately and to discharge each battery cell to a desired charge level using the power converters 702 and the charger/AC-to-DC converter(s) 410. Controller 408, for example, is capable of computing a joint current passing through battery 402 on the basis of information provided by the battery cell control cards, the charger, and the battery current monitor. In an embodiment, the battery current monitor is used for measuring a time integral of the current (i.e. a charge passing through the cells). Integration is effected, for example, either in the current monitor or is computed by controller 408. Each battery cell control card 700, for example, can be used for measuring or computing the current of a power converter 702, which is provided for example in parallel with the battery current, and the voltage across the poles of a battery cell, as well as other necessary parameters. The controller 408 is thus able to compute a joint capacity and efficiency for the battery cells using the monitored cell parameters. In addition, the discrepancies of each cell with respect to other cells can be computed from the monitored parameters and from the output of the battery current monitor. In practice, discrepancies may be generally measured more accurately than a joint capacity. This facilitates a precise equalization of the battery cells. As will be understood by persons skilled in the relevant art(s) given the description herein, the properties of an entire battery system are assessments at best, but the relative discrepancies between the battery cells of a battery can be measured with particular accuracy.
In an embodiment, the intentional overcharge of a battery cell stronger than others can be discharged during a discharging cycle to a greater depth than the others by having all other cells in a charging mode during the discharging cycle. In this case, the charge of a battery cell stronger than others will be exploited at a moderately high efficiency while other battery cells are in a charging process. Moreover, in an embodiment, the power converter associated with a battery cell stronger than others can be operated in a reverse sense during the discharging cycle. Hence, not only can inter-cellular discrepancies be equalized, but also the capacity of cells can be exhausted more thoroughly without neglecting to use any of the battery cells' capacity or without wasting energy.
In one embodiment, energy may be wasted for example by using just one voltage- or current-regulated joint charger and by dissipating outputs of the cells through resistances. In this case, battery cells can be bypassed in a charging process by using a low current for charging other cells or, instead of charging a single cell, by discharging the charge of all other cells for example by means of a resistance. Wasting energy may be more acceptable, for example, in the context of a solar-cell powered charger because of energy costs.
As will become apparent to persons skilled in the relevant art(s) given the description herein, the present invention functions very well using low cost/low quality electrical and electronic components as well as lower cost/lower quality batteries because of battery manager 406 and controller 408. Thus, the present invention offers significant benefits to electric utilities such as an ability to cost effectively alter their peak load demand by storing energy during off-peak electrical demand periods and by using the stored energy during periods of high demand instead of starting up and using higher cost generation units. The present invention can also be used to avoid grid congestion and to give utilities a means of cost effectively storing energy generated by clean energy power sources.
As shown in
In embodiments, user interface(s) 916 can be used to update and/or change programs and control parameters stored in a memory 902 of each power unit 116. This includes, for example, updating and/or changing a control program 904 and charger and inverter control variables 906 stored in a memory 902 of each power unit 116. By changing the control program and/or control parameters, a user can control the power units in any desired manner to alter the load demand of a power network such as, for example, power network 100. In an embodiment, the user interfaces can operate the power units to respond, for example, like spinning reserve and potentially prevent a major power brown out or black out.
In an embodiment, system 900 is used to learn more about the behavior of battery cells. Server(s) 912, for example, include logical and controlling modules that oversee the batteries of power units 116a-n and hold necessary information for controlling functions of the entire system 900. The system's server(s)/central processing units can be used, for example, for updating battery management algorithms for controlling the operation of the battery cells and for collecting and processing a considerable amount of information about the behavior of the entire system.
In an embodiment, information collected about the battery cells and operation of system 900 can be utilized by a manufacturer for example in neural networks or as material for an analysis conducted by statistical methods for developing a more effective future system. This telecommunication can also be used for varying algorithms in various units, for example, to increase the life of battery cells. Hence, in an embodiment, system 900 facilitates a research type environment that covers all power units that have been sold and which brings forth a more functional system to the benefit of all users and customers. For example, system 900 enables users to examine information collected and to determine how operating the batteries in a certain manner effects particular batteries and a predicted remaining service life of the batteries and system. Further features and benefits of system 900 will become apparent to persons skilled in the relevant art(s) given the description herein.
As will be understood by persons skilled in the relevant art(s) given the description herein, various features of the present invention can be implemented using processing hardware, firmware, software and/or combinations thereof such as, for example, application specific integrated circuits (ASICs). Implementation of these features using hardware, firmware and/or software will be apparent to a person skilled in the relevant art. Furthermore, while various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant art(s) that various changes can be made therein without departing from the scope of the invention.
It should be appreciated that the detailed description of the present invention provided herein, and not the summary and abstract sections, is intended to be used to interpret the claims. The summary and abstract sections may set forth one or more but not all exemplary embodiments of the present invention as contemplated by the inventors.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2009/062988 | 11/2/2009 | WO | 00 | 11/17/2011 |
| Number | Date | Country | |
|---|---|---|---|
| 61111650 | Nov 2008 | US |
