CA2381035A1

CA2381035A1 - Power management for hybrid battery systems

Info

Publication number: CA2381035A1
Application number: CA002381035A
Authority: CA
Inventors: Robert S. Feldstein; Joseph Rait
Original assignee: PowerGenix Systems Inc
Current assignee: PowerGenix Systems Inc
Priority date: 2002-04-09
Filing date: 2002-04-09
Publication date: 2003-10-09
Also published as: WO2003088405A2; WO2003088405A3; AU2003218565A8; AU2003218565A1

Abstract

A hybrid battery system has a power source, at least one battery charger, a hybrid battery module, and a load. The hybrid battery module comprises a high capacity battery and a high rate battery connected in parallel with each other, and an isolation diode connected between the output side of the high capacity battery and the high rate battery so as to permit charging current to flow from the high capacity battery to the high rate battery when the terminal voltage of the high rate battery falls below the terminal voltage of the high capacity battery by an amount at least equal to the forward bias voltage of the isolation diode. Typically, the terminal voltage of each of the high capacity battery and the high rate battery is substantially the same when both batteries are fully charged. The terminal voltage of the high rate battery will typically fall off under load conditions at a higher rate than the terminal voltage of the high capacity battery.

Description

POWER MANAGEMENT FOR HYBRID BATTERY SYSTEMS
FIELD OF THE INVENTION:
[0001 ] This invention relates to hybrid battery systems, and particularly to various configurations for managing power input and output to and from hybrid battery modules. In the present invention, a hybrid battery module comprises a high capacity battery and a high rate battery .connected in parallel.
BACKGROUND OF THE INVENTION:

[0002] The present invention is particularly directed to hybrid battery systems which may comprise a variety of configurations. The present invention is particularly directed to hybrid battery systems where a high capacity battery is combined with a high rate battery, with the batteries being connected one to the other, and in series with a load. Of course, there is a power source for the hybrid battery module, and in various embodiments of the present invention there may be a single charger or, more particularly, there may be two chargers provided, one for each of the high capacity battery and the high rate battery. The charger, is, of course, interposed between the power source and the hybrid battery module.
[ 0003] Moreover, the present invention also contemplates that various power sources or energy sources may be employed, including a conventional source of alternating current, as well as other sources such as fuel cells, and particularly power sources such as an internal combustion engine coupled to an alternator.
[0004] It is well known that there may be trade-offs between energy capacity and power delivery capability in the design of a battery. However, by combining two or more battery types, each with an intrinsic advantage in one area, which can be further optimised, a hybrid battery system c;an be provided.
~=0005] For example, it is well known that nickel zinc batteries have moderate power but excellent energy capabilities. Moreover, the energy capacity of a nickel zinc battery can be enhanced by optimising its design so as to sacrifice some rate capabilities, and so as to deliver power at high rates. If such a battery is combined with, for example, a lead acid battery, a hybrid energy storage system is provided.
[0006] If the lead acid battery is one which is optimised for high rate or power output, at the .expense of capacity, then the hybrid energy storage systems provides both superior rate capability .and capacity, due to the intrinsic values of the superior rate capability of the lead acid battery and 'the energy capacity of the nickel zinc battery.
[0007] As an example, if an electric vehicle is equipped with a hybrid battery system comprising a high capacity nickel zinc battery, and a high rate lead acid battery, then the vehicle 'would have substantially the range of the high capacity nickel zinc battery, and almost the acceleration and hill climbing capabilities of a vehicle equipped with a maximum power output lead .acid battery. Moreover, under regenerative braking conditions, the power absorption characteristics of the high rate lead acid battery will allow for quite efficient recovery of kinetic energy, thereby raising the overall efficiency of the vehicle.
[0008] However, with high capacity hybrid battery systems, in order to obtain high rate, it is important to be able to charge each battery type using an independently optimised algorithm, and to apportion the load appropriately as a function of demand and duration.
Obviously, such a system must be robust, economical, and reliable.
[0009] Ideally, in such a system, the batteries themselves should be the primary control elements, so that failure of either battery would still result in an operable surviving energy source having a degraded operating, but still existing, capability.
[0010] Some brief discussion of batteries and supercapacitors is appropriate, at this time, because while the following descriptions are particularly related to "battery"
systems, it can be understood that in some circumstances reference to a high rate, high power battery might also be appropriately made to a supercapacitor, as will be evident to those skilled in the art.
[0011] This discussion is particularly relevant to energy storage systems that have cored plates. Graded junction electrodes in such energy storage systems permit a large range of optimisation. At one end of the spectrum is an improved battery with excellent volumetric and weight energy and power density. Performance of such a device is driven by a minimized performance electrical and thermal support structure, which allows efficient use of active ingredients.

[0012] At the other end of the spectrum, the bulk of the active ingredients are traded Cur maximum boundary layer area, thereby providing maximum capacitance - that is a supercapacitor.
[0013] Of course, the range between high energy and high power density batteries and supercapacitors is a continuum. Several identifiable types of energy storage devices along that continuum include long service life batteries, or high cycle life batteries, high energy batteries, high performance batteries, ultra high power batteries, supercapacitors, high capacity supercapacitors, and ultra fast supercapacitors.
[0014] This design philosophy, in respect of a spectrum of energy storage devices, applies to such chemistries a lead acid and nickel zinc, for example.
[0015] Obviously, various kinds of energy storage devices are required for different :purposes. Telecommunications, power tools, handheld electronic devices. stand-by units. and so on.
;all have differing rate and capacity requirements, depending on the load and whether or not the load :is a constant load or a highly varying load.
[0016] One of the most difficult configurations for energy storage devices is in traction power devices such as electric motor vehicles, scooters, bicycles, motorcycles, and the like.
:Especially with respect to electric motor vehicles, which have considerable mass and which are expected to have a reasonable driving range and reasonable speed capabilities, the demands on an energy storage system are profound.
[0017] One approach to electric vehicles has been to use fuel cells. Fuel cells have certain advantages in that they are pure chemical devices, with an electrical output having no moving parts.
On the other hand, fuel cells have no storage capacity.
[0018] In a fixed load or base load application, the fuel cell capacity can easily be matched to the load, and the design of the fuel cell can be optimised for a single operating point.
[0019] On the other hand, vehicle propulsion requires a much more complex solution. Under variable load conditions, a fuel cell must be capable of providing for peak power requirements. That has two undesirable consequences: first, the capacity of the fuel cell must be increased, thereby increasing its size, weight, and cost. Second, the cell design will be compromised for power capacity and for average load efficiency.

3 [0020] However, fuel cells as a power source can be coupled with hybrid battery systems so as to provide load levelling. This is especially true if the battery can meet both peak power and peak duration requirements, and extended demand, as described above.
[0021 ] Various hybrid battery systems in various configurations are contemplated hereafter.
They include hybrid battery systems that may be useful in respect of electronic equipment such as Laptop computers and mobile telephones. Other systems are useful in respect of such loads as p~wcr tools, particularly handheld drills, wrenches, circular saws, and like.
[0022] Still other hybrid battery systems which are contemplated herein include those which will provide power to a DC to AC inverter which is used in stand-by operations for such as hospitals, large apartments and office buildings, and the like, where even in emergency conditions the AC load is widely varying - operating rooms must be kept going, elevators must be operated, heating and air ~;,onditioning systems must be maintained, and so on.
[0023] Finally, the present invention contemplates traction devices such as motor vehicles, where the traction power is delivered from an electrically operated traction motor.
SUMMARY OF THE INVENTION:
[0024] In accordance with one aspect of the present invention, there is provided a hybrid battery system having a power source, at least one battery charger, a hybrid battery module, and a load.
~'~0025] The hybrid battery module comprises a high capacity battery and a high rate battery, which are combined one with the other. An isolation diode is connected between the output sides of the high capacity battery and the high rate battery, in such a manner that charging current is permitted to flow from the high capacity battery to the high rate battery only when the terminal voltage of the high rate battery falls below the terminal voltage of the high capacity battery by an amount at least equal to the forward bias voltage of the isolation diode.
[0026] Typically, the terminal voltage of each of the high capacity battery and the high rate battery is substantially the same, when both batteries are fully charged.
Moreover, the batteries are such that the terminal voltage of the high rate battery falls under load conditions at a higher rate then t:he terminal voltage of the high capacity battery.

[0027] Typically, the forward bias voltage of the isolation diode is very low.
compared to the nominal fully charged terminal voltage of each of the high capacity battery and the high rate battery.
[0028] The load for the hybrid battery system may comprise a DC to AC
converter, and an AC load connected to the inverter.
[0029] In some circumstances, the high capacity battery may be a lithium ion battery, and the high rate battery may be a lead acid battery.
[0030] In such circumstances, the load is typically an electronic device such as a laptop or a handheld computer, a personal digital assistant (PDA), an electronic organiser, a mobile telephone, a digital or dual-operating mobile telephone, or combinations thereof.
[0031] In other configurations of hybrid battery systems in keeping with the present invention, the high capacity battery is a nickel zinc battery, and the high rate battery is a lead acid battery.
[0032] In such circumstances, the load may be a battery operated tool such as a drill, circular saw, screwdriver, wrench, router, jigsaw cutter, chainsaw, lawnmower, hedge trimmer, or combinations thereof.
[0033] Also, the power source may be an alternating current electricity source, a fuel cell, an internal combustion engine coupled to an alternator, and combinations thereof.
[0034] In circumstances particularly where the power source is an internal combustion engine coupled to an alternator, the load may be a traction motor which is connected to the hybrid battery module through a motor controller.
[0035] If so, then it is typical that each of the nickel zinc, high capacity battery and the lead acid, high rate battery, will be couple to the alternator through a respective first or second charger.
[0036] In that case, the first charger for the nickel zinc battery may be a precision, multi-step, constant charger. Such a charger is typically one whose current output is controlled by terminal voltage feedback from the nickel zinc battery.
~=0037] Moreover, the second charger for the lead acid battery may be a pulse pattern charger having voltage cut-off, a temperature compensated reference voltage, and an output which ranges from high current for fast charging of the lead acid battery to trickle current for maintenance charging of the lead acid battery.
[0038] Still further, the hybrid battery system of the present invention may be such that the charging capacity of each of the first and second chargers is matched to the output capacity of the alternator which is driven by an internal combustion engine. In that case, control for each of the chargers is such that the nickel zinc battery will be charged by the first charger only after the lead acid battery has been charged by the second charger.
[0039] Typically, of course, each of the chargers has its own voltage feedback controls.
[0040] Where each of the batteries of the hybrid battery module has its own charger, it may be that the fully charged terminal voltage of the lead acid battery is above the charger cutoff voltage ~of the first charger for the nickel zinc battery.
[0041] Typically, a motor controller for a traction motor, which is typically a polyphase induction motor, will be a bridge output polyphase pulse width modulated system.
[0042] However, the present invention also contemplates that the motor controller could be a delta modulator, particularly where the traction motor may be a polyphase induction motor, a lbrushless DC motor, a conventional DC motor, a pulse modulated motor, and reluctance motor, or combinations thereof.
[0043] Other hybrid battery systems contemplated by the present invention comprise a lithium ion high capacity battery combined with a nickel cadmium high rate battery; and a nickel metal hydride high capacity battery combined with a lead acid high rate battery.
BRIEF DESCRIPTION OF THE DRAWINGS:
[0044] The novel features which are believed to be characteristic of the present invention, as to its structure, organization, use and method of operation, together with further objectives and advantages thereof, will be better understood from the following drawings in which a presently preferred embodiment of the invention will now be illustrated by way of example. It is expressly understood, however, that the drawings are for the purpose of illustration and description only and ~~re not intended as a definition of the limits of the invention. Embodiments of this invention will now be described by way of example in association with the accompanying drawings in which:

[0045] Figure 1 shows a first typical configuration of a hybrid battery system in keeping with the present invention, where a single charger is employed;
[0046] Figure 2 is a second typical configuration of hybrid battery system in keeping with the present invention, where the load is an AC load which is feed through a DC
to AC inverter that derives power from the hybrid battery module;
[0047] Figure 3 is a typical configuration for a hybrid battery system in keeping with the present invention, where two chargers are employed, one for each battery in the hybrid battery module, and where the load is a traction motor which is controlled through a motor controller; and [0048] Figure 4 shows a typical power source arrangement for an electric vehicle that has an internal combustion engine as its primary energy source, and which delivers electrical energy through an alternator to the hybrid battery module;
:DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
[0049] The novel features which are believed to be characteristic of the present invention, as to its structure, organization, use and method of operation, together with further objectives and advantages thereof, will be better understood from the following discussion.
00050] Throughout the following discussion, with reference to the figures, like elements which are shown in various of the figures are identified by identical reference numerals.
[0051] A first typical configuration of hybrid battery system in keeping with the present invention, and the manner of power management thereon; is shown in Figure 1 at 1 U. l'his configuration, and others, comprises a power source 12, a charger 14, and a hybrid battery module 16. Within the hybrid battery module 16 there is a high capacity battery 18, and a high rate battery '?0. There is also an isolation diode 22. Connected to the hybrid battery module 16 is a load 24.
[0052] It will be noted that in each of the figures, the flow and direction of flow of electrical f.nergy is shown using arrowheads.
x_0053] Figure 2 differs from Figure 1 in that the load comprises a DC to AC
inverter 28. and an AC load 30.
[0054] It will be evident thus far that a hybrid battery system can be provided that will satisfy a number of different criteria, in different configurations, and for different purposes. For example, with respect to a configuration such as that shown in Figure 1, the high capacity battery can be such as a lithium ion battery; and the high rate battery can be such as a lead acid battery. The load might be an electronic device of some short, including laptop and handheld computers, personal digital assistants (PDAs), electronic organizers, mobile telephones, digital and dual-operating telephones, and combinations thereof. Particularly with respect to such devices as laptop computers and digital mobile telephones, they may have a widely varying load from time to time, depending on whether, for example, a disc drive is being operated, speakers are being operated, whether a telephone is in .a receive or transmit mode, and so on. Also, it will be evident that peak power problems at low estate-of charge conditions can be obviated by the present invention.
[0055] For example, it may be assumed with respect to Figure 1 that the hybrid battery :module and the load are separated from the power source and the charger during operating conditions. As the load is turned on, the high rate battery 20 will first provide electrical power to the load, although there will initially be load sharing as well between the batteries. However, as the high rate battery depletes, its terminal voltage will fall off fairly rapidly.
At that time, if the terminal voltage of the high rate battery 20 has fallen below the terminal voltage of the high capacity battery 18 by an amount greater than the forward bias voltage of the isolation diode 22, then the high capacity battery 18 will start to recharge the high rate battery 20.
[0056] Moreover, the high rate battery is such that its terminal voltage recovery will be quite rapid, and thus there is load sharing and recharging of the high rate battery from the high capacity battery, contemporaneously.
[0057] At a later time, the hybrid battery module 16 will be reconnected to the charger 14, at which time the high capacity battery 18 and the high rate battery 20 will be charged from the power source 12.
[0058] However, typically the charger is a relatively low capacity charger, and thus the high rate battery 20 will typically be charged first, before the high capacity battery 18 is charged, as a consequence of appropriate voltage feedback and control circuits within the charger 14, and most particularly as a consequence of the intrinsic lower input impedance of the high rate battery 20 and therefore its propensity to absorb charge first.

[0059] A similar configuration such as that shown in Figure l, but where the high capacity battery is a nickel zinc battery, and the high rate battery is a lead acid battery, may be employed in such circumstances where the load 24 is such as a power tool. Power tools may include handheld battery operated tools such as drills, circular saws, screwdrivers, wrenches, routers, jigsaw cutters, chainsaws, and the like, as well as lawnmowers and hedge trimmers, and the like. In circumstances such as when the rotor of the driving motor in the load 24 becomes almost stalled or locked, then the high rate battery 20 will provide driving energy to the load, while at the same time it will be :recharged from the high capacity battery 18.
[0060] Other examples of hybrid battery systems that are also contemplated by the present invention are a lithium ion high capacity battery combined with a nickel cadmium high rate battery;
and a nickel metal hydride high capacity battery combined with a lead acid high rate battery.
j[0061 ] Figure 2 contemplates the use of a DC to AC inverter 28 which provides power to an .AC load, in stand-by and energy back-up power system configurations. ~1s noted above, the .AC' lead may vary widely, thereby drawing power from the high rate battery 20 in the first instance, and providing for recharge of the high rate battery and supplemental energy delivery from the high rapacity battery 18.
[0062] Typically, in such circumstance, the capacity ofthe high capacity 18 is very high, and the batteries will be recharged from the charger 14 after the power source 12 has been reconnected or recovered.
[0063] Other stand-by circumstances, where there may be a highly valuable power demand requirement, include solar and wind power generators, forklift trucks, switch gear back-up i.nsulations, and the like. Still other cyclically operating, variable power demand requirements may be made from people movers such as escalators, moving walkways, elevators, and the like, which operate on demand.
[0064] A principal configuration in respect of the present invention lies in the field of motive and traction devices, such as bicycles, motorcycles, scooters, and the like, and also in respect of motor vehicles.
x:0065] Typically, such motor vehicles are referred to as electric motor vehicles or hybrid motor vehicles, depending on whether the energy source per se is such as a fuel cell, or an internal combustion engine. It is particularly to those configurations of electric vehicles where the primary energy source is an internal combustion engine that the following discussion is directed.
[0066] Reference is made to Figures 3 and 4. Here, it will be seen that the high capacity battery 18 and the high rate battery 20 each have their own respective chargers 32 and 34. Thus, the operation and charging functions of the charger/battery combinations are essentially independent one of the other, subject to the discussion which is made below.
[0067] It will be noted that the load of the hybrid battery module 16 is a traction motor 38, which is controlled through a motor controller 36.
[0068] Typically, as shown in Figure 4, the power source 12 comprises an internal .combustion engine 40 which is coupled to an alternator 42, and that in turn provides electrical energy to the chargers 32 and 34, in the manner described hereafter. However, fuel cells may be employed as a primary power source as well.
10069] Particularly with respect to the embodiments of Figures 3 and 4, there is typically a requirement to charge each of the batteries 18 and 20 independently, using separate charge algorithms and the like, but for there to be load share as a function of power demand and duration.
:Moreover, there may also be the requirement for the batteries to accept high recharge inputs in the event of regenerative braking conditions of the vehicle.
[0070] As stated, a traction configuration of hybrid battery system in keeping with the present invention, and particularly in respect of the power management therefore, contemplates the use of a high capacity nickel zinc battery and a high rate lead acid battery, each having their own chargers.
[0071] Moreover, because the primary motor power delivered to the traction motor 38 is from the hybrid battery module 16, the internal combustion engine 40 may be a constant speed, ultra-).ow emission gasoline powered engine. It, of course, is connected to an alternator 42, and then to l:he separate chargers 32 and 34.
[0072] Regenerative braking may be applied only to the high rate battery 20 -the lead acid battery system - as noted hereafter.

[0073] The nature of the charger 32 for the nickel zinc high capacity battery 18 may be such that it is a precision multi-step constant current charger. The current of such a charger is determined by the voltage feedback from the battery.
[0074] Also, the nature of the charger 34 for the lead acid battery may be such that it is a pulse pattern charger having voltage cut-off. Typically, such a charger is provided with a temperature compensated voltage reference, and it is such that it will output a small constant current or trickle charge for battery maintenance purposes, as well as to output a high current for initial battery charge purposes.
[0075] Generally, the energy capacity of the lead acid battery 20 is much smaller than that of the nickel zinc battery 18; but on the other hand, the capacity of the charger 34 is equal to that of the charger 32, and most typically the capacity of both chargers 32 and 34 is essentially the same as the output capacity of the alternator 42.
[0076] If so, then generally there will be a simple inter-charger control algorithm which provides that the nickle zinc battery will be charged only after the lead acid battery has been charged.
Thus, maximum use of the available alternating capacity is obtained, since the two chargers will not necessarily be operated simultaneously.
[0077] In that case, a single set of power components such as a steered output cabling and the like, together with separate feedback controls, will typically be provided.
[0078] Of course, the control algorithms for the charger 32 and 34 may be implemented in a shared microprocessor.
[0079] Since the two chargers 32 and 34 may not necessarily operate simultaneously, the heat output and cooling requirement from them will generally be relatively constant, and a common package of shared components and cooling for the chargers will represent an economic and size/weight advantage.
[0080] The high rate lead acid battery 20 may be configured to have a full charge voltage which is slightly above the charger cutoff voltage of the charger 32 for the nickel zinc high capacity battery 18. If so, then the isolation diode 22 will provide for load sharing control.
[0081 ] For example, if the starting state for both batteries is that they are fully charged, then the initial power demand will be met from the high rate lead acid battery 20.
However, due to its small capacity, and the output voltage characteristics of such high rate lead acid batteries, and the like, the terminal voltage of the lead acid battery 20 will rapidly drop to the "catcher" voltage of the nickel zinc, high capacity battery 18. Put in other words, the voltage drop will equal or exceed the forward bias voltage of the isolation diode 22.
[0082] Thereafter, the load will be primarily supported by the high capacity nickel zinc battery 18, due to its substantially larger capacity, for so long as the load requirements exceed the charger output capacity.
[0083 ] If the load energy requirements are less than the charger output capacity of the charger 32, than the high rate lead acid battery 20 will be charged to its capacity, and the traction motor will then be fed essentially by the alternator 42, so as to effectively be engine powered from the engine 40. In such circumstances, of course, the high capacity nickel zinc battery 18 will essentially float.
[0084] It should be noted that even if the load exceeds the alternator capacity, then periodic stops or load decrease, such as in a downhill operating condition ofthe vehicle, will provide recharge opportunities for the nickel zinc high capacity battery 18 in particular.
Indeed, even after the vehicle is parked, if there is adequate ventilation provided, then continuing recharge of the hybrid battery system, and particularly the high capacity battery 18, can be maintained.
[0085] Of course, prolonged partial state-of charge operation of lead acid systems is not generally desirable. However, the varying nature of the load, particularly when a vehicle is being operated from the traction motor 38, more closely resembles a shallow discharge cyclic service for the lead acid battery, which such lead acid batteries will tolerate quite well.
[0086] It can be considered for purposes of the present discussion that the traction motor 3 8 may be a polyphase induction motor. Of course, it may also be such as a brushless DC motor, a conventional DC motor, a pulse modulated motor, or a reluctance motor.
(0087] In such circumstances, particularly, where the traction motor is a polyphase induction motor, such a motor is efficiently bidirectional - that is, it will function as a motor but, in some circumstances, with a reversed field, it will function as a generator.
[0088] Thus, the motor control may be a conventional bridge output polyphase pulse width modulation system. Also, regenerative braking energy will be returned entirely to the lead acid high rate battery 20, due in part of the presence of the isolation diode 22, and because an intrinsic characteristic of the lead acid battery is its capability to absorb energy at very high rates.
[0089] However, it should be noted that typically regenerative braking energy may be directed to both batteries in the hybrid battery system so as to provide maximum charge absorption.
'There may be an override in respect of the isolation diode, which override may function in regenerative braking conditions, so as to assure maximum charge absorption and the best efficiency, ,accordingly.
[0090] It is generally considered that the total kinetic energy of the vehicle is typically not sufficient to damage the lead acid system in the high rate battery 20 as a consequence of overcharge;
'but a panic stop from high speed, for example, could be excessive and produce unacceptable thermal excursions.
[0091 ] Thus, and in any event, a mechanical braking system is required for such a vehicle -- for purposes of safety and redundancy. Accordingly, a motor control algorithm - that is, a safety limit - can be included with the motor controller 36 so as to limit regenerative braking from the traction motor 38 when functioning bidirectionally as a generator, by adding electrodynamic braking ;end finally mechanical braking.
[0092] Moreover, for purposes of public safety and acceptance requirements, in panic stop situations, in particular, it is accepted that there will be energy loss, which might briefly reduce the energy efficiency of the system, but only in such panic stop circumstances.
x_0093] It will be understood from the above discussion, that, in fact, the state of charge of each battery in the combination which comprises a hybrid battery system in keeping with the present invention, together with the charge acceptance capacity of each of those batteries and the magnitude of recharge for each of those batteries will vary depending on the systems employed, and the conditions in which the are employed.
[0094] Of course, it will be understood, as noted above, that each of the Figures is quite simplified in its presentation, as the details of any specific hybrid battery configuration in a specific load and charge condition requirement, are beyond the scope of the present invention.
[0095 ] It will be noted that, particularly in motive power applications, an internal combustion engine may also be used in parallel as well as in a series configuration as described above. In other words, in addition to the electrical load provided by the alternator to the internal combustion engine, a direct shaft contribution from the internal combustion engine to deliver motive power to the driving wheel or wheels of a vehicle, may also be employed.
[0096] Of course, it will be understood that complex battery management systems wil l allow combinations of more than two battery types, all at arbitrary voltages, which may be combined in a sophisticated load sharing and recharge sharing scheme. Such a configuration is, therefore. a natural extension of the typical configurations which have been described above.
[0097] A power management system for hybrid battery systems, in various configurations, has been shown and described. It would be evident that amendments and alterations to such systems can be made without departing from the spirit and scope of the appended claims.
[0098] Throughout this specification and the claims which follow, unless the context reduires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not to ohe exclusion of any other integer or step or group of integers or steps.

Claims

WHAT IS CLAIMED IS:

1. A hybrid battery system having a power source, at least one battery charger, a hybrid battery module, and a load;
wherein said hybrid battery module comprises a high capacity battery combined with a high rate battery, and an isolation diode connected between the output side of each of said high capacity battery and said high rate battery;
whereby charging current is permitted to flow from said high capacity battery to said high rate battery only when the terminal voltage of said high rate battery falls below the terminal voltage of said high capacity battery by an amount at least equal to the forward bias voltage of said isolation diode.

2. The hybrid battery system of claim 1, wherein the terminal voltage of each of said high capacity battery and said high rate battery is substantially the same when both batteries are fully charged, and wherein the terminal voltage of said high rate battery falls off under load conditions at a higher rate than the terminal voltage of said high capacity battery.

3. The hybrid battery system of claim 2, wherein the forward bias voltage of said isolation diode is low compared to the nominal fully charge terminal voltage of each of said high capacity battery and said high rate battery.

4. The hybrid battery system of claim 1, wherein said load comprises DC to AC
inverter, and an AC load connected thereto.

5. The hybrid battery system of claim 1, wherein said high capacity battery is a lithium ion battery, and said high rate battery is a lead acid battery.

6. They hybrid battery system of claim 5, wherein said load is an electronic device chosen from the group consisting of laptop and handheld computers, personal digital assistants (PDAs), electronic organizers, mobile telephones, digital and dual-operating mobile telephones, and combinations thereof.

7. The hybrid battery system of claim 1, wherein said high capacity battery is a nickel zinc battery, and said high rate battery is a lead acid battery.

8. The hybrid battery system of claim 7, wherein said load is a battery operated power tool chosen from the group consisting of drills, circular saws, screwdrivers, wrenches, routers, jigsaw cutters, chainsaws, lawn mowers, hedge trimmers, and combinations thereof.

9. The hybrid batter system of claim 1, wherein said power source for said at least one charger is chosen from the group consisting of alternating current electricity, fuel cells, internal combustion engines coupled to alternators, and combinations thereof.

10. The hybrid battery system of claim 7, wherein said power source is an internal combustion engine coupled to an alternator, and wherein said load is a traction motor connected to said hybrid battery module through a motor controller.

11. The hybrid battery system of claim 10, wherein each of said nickel zinc, high capacity battery and said lead acid, high rate battery is coupled to said alternator through a respective first and second charger.

12. The hybrid battery system of claim 11, wherein said first charger for said nickel zinc battery is a precision, multi-step, constant current charger whose current output is controlled by terminal voltage feedback from said nickel zinc battery; and wherein said second charger for said lead acid battery is a pulse pattern charger having voltage cut-off, a temperature compensated reference voltage, and an output ranging from high current for fast charging of said lead acid battery to trickle current for maintenance charging of said lead acid battery.

13. The hybrid battery system of claim 11, wherein the charging capacity of each of said first and second chargers is matched to the output capacity of said alternator, wherein control for each of said chargers is such that said nickel zinc battery will be charged by said first charger only after said lead acid battery has been charge by said second charger; and wherein each charger has its own voltage feedback controls.

14. The hybrid battery system of claim 13, wherein the fully charged terminal voltage of said lead acid battery is above the charger cutoff voltage of said first charger for said nickel zinc battery.

15. The hybrid battery system of claim 11, wherein said motor controller for said traction motor is a bridge output polyphase pulse width modulated system, and said traction motor is a polyphase induction motor.

16. The hybrid battery system of claim 11, wherein said motor controller is a delta modulator, and said traction motor is chosen from the group consisting of polyphase induction motors and brushless DC motors, conventional DC motors, pulse modulated motors, reluctance motors, and combinations thereof.

17. The hybrid battery system of claim 1, wherein said high capacity battery is a lithium ion battery, and said high rate battery is a nickel cadmium battery.

18. The hybrid battery system of claim 1, wherein said high capacity battery is a nickel metal hydride battery, and said high rate battery is a lead acid battery.