WO2011114349A2

WO2011114349A2 - Hybrid battery pack

Info

Publication number: WO2011114349A2
Application number: PCT/IN2011/000165
Authority: WO
Inventors: Chetan Kumar Maini; Ramaraju Prakash; Syrus Romeo Nedumthaly
Original assignee: Mahindra Reva Electric Vehicles Pvt. Ltd
Priority date: 2010-03-15
Filing date: 2011-03-11
Publication date: 2011-09-22
Also published as: WO2011114349A3

Abstract

A hybrid battery pack has a first battery (10) with a plurality of first cells (11) connected in series and a second battery (20) with a plurality of second cells (21) connected in series. The first and second batteries (10 and 20) each have a different chemistry and are connected in parallel. A method for identifying batteries having an optimum combination for a hybrid battery pack includes obtaining information related to a load profile (100) for an electric device in which the hybrid battery pack is adapted to be used. Further, information about an initial state of charge (101) of each cell in a first and a second battery, respectively and information related to number of cells and a nominal capacity of each battery string (103) is obtained. The information thus obtained is sent to an equivalent circuit (104) for determining the optimum combination.

Description

"HYBRID BATTERY PACK"

FIELD OF INVENTION

[001] The disclosed embodiments relate generally to a battery pack having different types of batteries connected to each other and used as a single energy source and more particularly, but not by way of limitation, to a hybrid battery pack having an optimum combination of different types^' of batteries and a method for identifying the batteries for the optimum combination.

BACKGROUND

[002] In the recent days, use of electrical devices has dramatically increased resulting in sophistication of these electrical devices from time to time. Generally, higher the reliance upon electrical devices in the field of transportation, businesses, education and likewise, calls for a reliable source of power for the electrical devices. The electrical devices which use electrical energy as the source of power include an energy storage system. The energy storage system may be a Lithium Ion Phosphate battery pack, a Lead Acid battery pack, a Lithium Ion Cobalt battery pack and other similar battery packs.

[003] For example, electric vehicles and hybrid automobiles rely on batteries to power the motor system and to obtain an increased overall efficiency. Lead acid batteries are the oldest type of batteries used in electric vehicles. The lead acid batteries were usually used as a stand-alone source of power because they are easy to manufacture, less expensive and fairly durable. However, the lead acid batteries are generally heavier and have lower cycle life. There are many other types of batteries, for example lithium ion batteries, which were introduced after the lead acid batteries and that are capable of powering an electric vehicle. The lithium ion batteries are light in weight and have a higher cycle life as compared with the lead acid batteries. However, the lithium ion batteries are more expensive than the lead acid batteries.

[004] There are many portable power supply systems or battery packs using hybrid battery technology. For example, it has been proposed that a portable power supply system or battery pack may contain two different types of batteries. The first battery of the portable power supply system or battery pack is chosen so as to have a high discharge rate and high peak amperage and the second battery is chosen so as to have a high energy density and less expensive. The electrical characteristic of each of the battery is configured such that the second type of battery is able to recharge the first type of battery.- The afore-mentioned power supply system or battery pack may have limited use in that the power system only provides a large amount of current needed to start an electrical device over a short period of time, for example an engine. However, the aforementioned power system or battery pack may not be used for an electrical device which uses the power for a long period of time, for example, an electric vehicle. Further, the afore-mentioned power supply system or battery pack does not consider the load profile of the electric device while combining the two different types of batteries. The power supply system or battery pack in a conventional electric vehicle is made of a single battery type such as a 48 volts, 200 Ah lithium ion phosphate battery pack made of 16 cells in series, a 48 volts, 160Ah lead acid battery pack made of 24 cells in series and a 72V, 200Ah lithium ion cobalt battery pack made of 21 cells in series. [005] In view of the above reason(s), there is a need for a hybrid battery pack having an optimum combination of different types of batteries and a method for identifying the batteries for the optimum combination. OBJECT

[006] An object is to provide a hybrid battery pack having different types of battery.

[007] A further object is to provide a method for identifying the batteries for optimum combination in the hybrid battery pack.

STATEMENT OF INVENTION

[008] Accordingly an embodiment provides a hybrid battery pack having a first battery with a plurality of first cells connected in series and a second battery with a plurality of second cells connected in series. The first and second batteries each have different chemistry. The first and second batteries are connected in parallel. The first battery may or may not have a discharge rate more than that of the second battery. Further, a discharge rate of each of the first and second batteries may be equal. Further, one of the batteries may or may not be adapted to have a longer cycle life than the other. [009] There is also provided a method for identifying batteries having an optimum combination for a hybrid battery pack. The method includes obtaining information related to a load profile for an electric device in which the hybrid battery pack is adapted to be used. The method further includes obtaining information about an initial state of charge of each cell in a first and a second battery, respectively. Further, information related to number of cells and a nominal capacity of each battery string is obtained. The information related to the load profile, the initial state of charge of each cell, information on number of cells in each of the first and second batteries, and a nominal capacity of each battery string, thus obtained is sent to an equivalent circuit for determining the optimum combination.

[0010] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

BRIEF DESCRIPTION OF FIGURES

[0011] Embodiments are illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:

[0012] FIG. 1 depicts batteries of different chemistry connected to each other in a hybrid battery pack, according to an embodiment as disclosed herein; [0013] FIG. 2 illustrates a flow chart for identifying an optimum combination of the types of batteries to be used in the hybrid battery pack;

[0014] FIG. 3 depicts a non-limiting electrical equivalent circuit model of FIG. 1; and

[0015] FIG. 4 is a graph depicting a state of charge, of each of a lead acid flooded tubular battery and lithium ion iron phosphate battery, in relation to the time.

DETAILED DESCRIPTION

[0016] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description.

Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

[0017] The embodiments herein achieve an optimum combination of different types of batteries in a hybrid battery pack by providing a method for identifying the batteries for the optimum combination. Referring now to the drawings, and more particularly to FIGS. 1 through 3, where similar reference characters denote corresponding features consistently throughout the figures, there are shown embodiments. [0018] FIG. 1 depicts batteries 10 and 20 of different chemistry connected to each other in a hybrid battery pack (not shown). The battery 10 has a plurality of cells 11 connected in series. The battery 20 has a plurality of cells 21 connected in series. The batteries 10 and 20 are connected in parallel so as to form a hybrid battery pack (not shown). It should be noted that for the purpose of understanding, the embodiments will be described by considering a battery pack having only two batteries 10 and 20. However, it will be apparent to a person having ordinary skill in the art that the embodiments may be practiced by employing more than two batteries and hence such employment of more than two batteries also falls within the scope of the present invention.

[0019] Further, FIG. 2 illustrates a flow chart for a method of identifying an optimum combination of the types of batteries to be used in the hybrid battery pack. The method 99 for identifying an optimum combination includes, obtaining a typical drive profile as shown in step 100 of a particular electric device (not shown). The typical drive profile 100 is data corresponding to load current and the time. Further, an initial state of charge of, as shown in step 101, each of the batteries 10 and 20 is obtained.

[0020] Further, in order to determine state of the combination of the batteries 10 and 20, the information related to the typical drive profile as shown in step 100, the information related to the initial state of charge of each of the batteries 10 and 20 as shown in step 101 as well as number of cells 11 and 21 in each of the batteries and a nominal capacity of each of the battery string as shown in step 103 is sent to an equivalent circuit as shown in step 104. The equivalent circuit as shown in step 104 is made up of a variable open circuit voltage OCV and variable internal resistance IR of each of the batteries 10 and 20. The state of combination is a combined effective battery pack voltage and state of charge of the batteries 10 and 20. The desired minimal optimal behavior of the combination of the batteries 10 and 20 should be such that an effective voltage of the hybrid battery pack should be more than a desired minimum threshold voltage and each of the batteries 10 and 20 should not have discharged more than their respective nominal capacity at the end of load profile. Further, a state of charge SOC1, an open circuit voltage OCV1 and an internal resistance IR1 of the battery 10 as depicted in step 111 is sent to the equivalent circuit model as shown in step 104. Similarly, a state of charge SOC2, an open circuit voltage OCV2 and an internal resistance IR2 of the battery 20 as depicted in step 112 is sent to the equivalent circuit model as shown in step 104.

[002 Ϊ] Further, a relation between the respective state of charge SOC1 and open circuit voltage OCV1 of each of the batteries 10 and 20 is stored as a look up table for future retrieval. Similarly, a relationship between the respective state of charge SOC2 and internal resistance IR2 of each of the batteries 10 and 20 is stored as a look up table for future retrieval.

[0022] The equivalent circuit model as shown in step 104 determines as to whether the state of combination of the batteries 10 and 20 is above the desired rninimum optimal behavior as shown in step 105. If the state of combination of the batteries 10 and 20 is not above the desired minimum optimal behavior, then the combination of the batteries 10 and 20 is not considered to be feasible as depicted in step 106. However, if the state of combination of the batteries 10 and 20 is above the desired minimum optimal behavior, then whether the drive profile is complete or not is determined as depicted in step 107. If the drive profile is not complete, then a new state of charge for each of the batteries 10 and 20 is determined. The new state of charge is calculated based on a respective branch current. Further, the new state of charge for each of the batteries 10 and 20 to form an optimum combination is determined. The new state of charge for each of the batteries 10 and 20 is sent to the equivalent circuit to determine the completeness of the drive profile.

[0023] Further, if the drive profile is complete, then it is determined as to whether the final state of combination of the batteries 10 and 20 meets the desired requirement as shown in step 108. If the final state of combination is as desired, then the combination of the batteries 10 and 20 is considered as useful as depicted in step 110. Further, if the final state of combination is not as desired, then the combination of the batteries 10 and 20 is considered as not useful as shown in step 109.

[0024] Further, FIG. 3 depicts an electrical equivalent circuit model of FIG. 1 according to another embodiment. The embodiment depicted in FIG. 3 is an example and hence should not be considered as limiting. The battery 10 may be a Lithium Ion battery having a plurality of cells each having a voltage VI and resistance Rl. The battery 20 may be a Lead Acid battery includes a plurality of cells each having a voltage V2 and resistance R2.

[0025] It was confirmed from one of the experiments conducted that a combination of 80% of Lead acid and 20% Lithium Ion is a combination resulting in an optimal behavior. FIG. 4 is a graph depicting a state of charge, of each of a lead acid flooded tubular battery and lithium ion iron phosphate battery, in relation to the time. Further, table 1 shows the nominal capacity in Ahr, number of cells, state of charge at the start in percentage (%) and state of charge at the end in percentage (%) for each of the Lithium Ion-Iron Phosphate and Lead Acid-Flooded Tubular battery types, respectively.

TABLE. 1

[0026] Further, it is also within the scope of the invention that a connect- disconnect type system be implemented for the electrical device to use only one of battery 10 or battery 20 or the combination of batteries 10 and 20.

[0027] The various actions in method 99 may be performed in the order presented, in a different order or simultaneously.

[0028] The embodiments disclosed herein can be implemented through at least one software program running on at least one hardware device and performing network management functions to control the network elements.

[0029] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Claims

WE CLAIM;-

1. A hybrid battery pack comprising:

a first battery having a plurality of first cells connected in series; and a second battery having a plurality of second cells connected in series, said second battery having a different chemistry than the first battery, wherein said first battery and second battery are connected in parallel.

2. The hybrid battery pack as claimed in claim 1, wherein a combination of the first and the second battery is determined based on a load profile, an initial state of charge of each cell in the first battery and the second battery, number of cells and a nominal capacity of the batteries.

3. The hybrid battery pack as claimed in claim 2, wherein the first battery is a lithium ion battery and the second battery is a lead acid battery.

4. The hybrid battery pack as claimed in claim 1, wherein one of the batteries has a longer cycle life than the other.

5. The hybrid battery pack as claimed in claim 1, wherein said first battery has a discharge rate more than the second battery.

6. A method for identifying combination of batteries for a hybrid battery pack, said method comprising:

obtaining information related to a load profile for an electric device in which the hybrid battery pack is adapted to be used; obtaining information on an initial state of charge of each cell in a first and a second battery, respectively; and

providing the information related to the load profile and the initial state of charge of each cell along with information on number of cells in each of the first and second batteries and nominal capacity of each of the batteries to an equivalent circuit for deterrnining the combination.

7. The method as claimed in claim 6, wherein the first battery has a different chemistry than the second battery.

8. The method as claimed in claim 6, wherein said method further comprises the step of determining a desired optimum behavior of the combination based on the load profile.

9. The method as claimed in claim 8, wherein said determining the desired optimum behavior of the combination is carried out prior to the step of providing the information.

10. The method as claimed in claim 6, wherein the first battery has a discharge rate more than a discharge rate of the second battery.

11. The method as claimed in claim 6, wherein one of the batteries has a longer cycle life than the other.

12. The method as claimed in claim 11 , wherein the first battery is a lithium ion battery and the second battery is a lead acid battery.

12. An apparatus substantially as herein above described in the specification with reference to the accompanying drawings.

13. A method substantially as herein above described in the specification with reference to the accompanying drawings.