Method and apparatus of stored energy management in battery powered vehicles

A secondary battery and charging system are provided within an electric car or other electric drive vehicle. The secondary battery may, e.g., be owned by the electric utility. The battery is removable and can be charged and discharged independently of the primary car battery system. The utility can use the secondary battery to implement vehicle-to-grid functionality.

FIELD OF THE INVENTION

The invention relates to the storage and utilization of electricity in vehicles that derive at least some power from batteries.

ART BACKGROUND

It has long been known that distributed schemes for production, storage, and retrieval of electric energy can make electric power distribution by public utilities more cost effective. For example, small or medium-scale facilities storing energy in the form of charged batteries, pumped water, compressed gas, or the like can be connected to the electric power grid and used to add power to the grid during outages and periods of high demand. Conversely, the distributed storage facilities can draw energy from the grid during periods of excess production or low demand, and store the energy for future use. Economic incentives can be provided to the owners of the storage facilities. This can be advantageous to the utilities through a reduction in the fluctuation of demand for electric power. Thus, it can help them to meet their commitments for the delivery of electric power without making capital investments in excess production capacity. The term “load balancing” is often used to refer to schemes of this kind.

One example of a small-scale energy storage facility is the battery system in an electric drive vehicle. Such a battery system may be charged exclusively from the electric power grid, or it may be charged through on-board electrical generation (consuming liquid or gaseous fuel), or it may be charged through some combination of the two preceding methods. Although the electric-drive vehicles that have received the most attention recently are automobiles (“electric cars”), other electric drive vehicles of interest in this context include trucks, and possibly also boats and trains.

In so-called “vehicle-to-grid (V2G)” schemes, the batteries within electric cars (or other electric drive vehicles) are connected, at times, to the power grid and used for load balancing. Such schemes have been under discussion at least since the publication in 1997 of the paper by W. Kempton and S. E. Letendre, “Electric Vehicles as a New Power Source for Electric Utilities.”Transpn. Res.-D, vol. 2, no. 3, (1997), pp. 157-175.

The premise of V2G is that the battery within an electric car represents an unused resource when the car is not being used. When deployed to a large portion of the population of a city, this unused resource has a significant electrical power storage capability. Therefore, the electrical power utility could charge or discharge the batteries of electric cars which are plugged into the power grid, e.g. while the owners are at work, shopping, or at home. The charging or discharging would be timed to reduce fluctuations in supply and demand, with the possible beneficial consequences that primary production capacity is used more efficiently and overall electrical consumption is reduced.

One drawback of V2G as currently envisaged is that it may have limited acceptability to consumers. That is, a typical consumer will consider it desirable to always maintain the battery in a full (i.e., fully charged) condition, whereas the utility company will want to alternately charge and discharge the battery according to fluctuations in supply and demand. This poses a problem not only because the consumer will view the utility company's use as denying him the full benefit of his property (i.e., the battery), but also because every car battery has a limited number of charge/discharge cycles, and the utility company's use will therefore reduce the lifetime of the battery.

Of course, the utility company may provide incentives to the consumer in the form of reduced electricity prices, or ownership of the batteries within the car may be transferred to the utility. Although this may overcome some resistance by consumers, the basic conflict between maintaining a full charge and permitting charge flexibility is left unresolved.

SUMMARY OF THE INVENTION

Our solution is to provide a secondary battery and charging system within an electric car or other electric drive vehicle. The secondary battery may, e.g., be owned by the electric utility. The battery is removable and can be charged and discharged independently of the primary car battery system. The utility can use the secondary battery to implement V2G functionality without the constraints on usage described previously. If, e.g., the secondary battery is not owned by the user, there is less cause for the user to resist participation in V2G.

Accordingly, in an embodiment, a power assembly includes a primary battery unit and a secondary battery unit that has no more than 20% the total discharge capacity of the primary battery unit and is removable from the primary unit. The power assembly further includes switching circuitry configured to selectively draw electric power from one or the other of the primary and secondary battery units, and switching circuitry configured to independently charge the primary and secondary battery units. By “independently” is meant that each battery unit can be charged without substantially affecting the charging rate of the other, and that at least one can be charged without charging the other.

The power assembly further includes a battery management system (BMS) and a controller configured to receive battery charge state information from the BMS. The controller is configured to control the charging or discharging of the batteries in response to local commands that are input from, e.g., the driver of the vehicle. The controller is also configured to permit remote control on condition that a remote entity has been authenticated, and to control the charging or discharging of at least the secondary battery unit in response to commands from the remote entity.

In a more particular embodiment, the controller is further configured to control the charging or discharging of at least the secondary battery unit subject to a policy that is stored locally, e.g. in the controller or elsewhere in the vehicle.

In some embodiments, the controller is user programmable, such that the locally stored policy is configurable or selectable by a local user such as the driver of the vehicle.

In some embodiments, the power assembly further comprises a communication unit configured to communicate the charge state of the secondary battery unit to a remote location.

In some embodiments, the communication unit is further configured to communicate the location of the secondary battery unit.

In some embodiments, the communication may provide dynamic updates to electrical pricing to the BMS. This information may be used to set a local charging policy.

DETAILED DESCRIPTION

FIG. 1shows a typical scenario in which electric cars may be placed in contact with an electric utility for purposes of load balancing. Employee cars10are parked in parking lot20of workplace buildings30. An electric power plant40is advantageously situated relatively nearby to minimize transport loss.

Power line50delivers electric power from the power plant to utility box60, from which it is distributed to each of the parking spaces of lot20by conductive distribution lines70. At each parking space, the electrical storage assembly of the respective car plugs into a receptacle (not shown) in electrical contact with one of the lines70. The receptacle provides electrical continuity for charging and discharging the car's batteries.

It is also advantageous to provide a communication medium between the car and the electric utility, for example so that the utility can read the state of charge of the car batteries. Various alternative communication media are known. These include an additional communication cable to which the car may connect by plugging into the same receptacle that provides electrical continuity. Alternatively, communication may take place over the power cable using powerline carrier (PLC) techniques, or communication may take place wirelessly.

With further reference toFIG. 1, connection to the electric utility may also be provided to an electric car80when parked in driveway90of its owner's house100. As described above, power line50delivers electric power to a utility box60, to which the car connects via a plug and receptacle arrangement, for example.

In accordance with the illustrated scenario, power may be drawn from the cars in lot20during times of peak demand in the middle of the day, when the cars are sitting idle. On the other hand, power may be delivered for recharging car80during times of low demand in the middle of the night, while car80is likewise sitting idle.

Turning now toFIG. 2, there is illustrated a possible battery assembly according to an embodiment of the present invention. The battery assembly is installed in a rear compartment of car110. As seen in the figure, a primary battery unit120is permanently installed in the car. By “permanently” is meant that it is not readily removable, but may be wholly or partly removable with significant effort, for purposes of replacement and repair.

As also seen in the figure, a secondary battery unit130is removably installed in the car. By “removably” is meant that the secondary battery unit can be removed with minimal effort, other than that necessary to operate a release mechanism and to handle an object that may weigh up to several hundred pounds. Various configurations are possible for holding and supporting the secondary battery unit130. For example, unit130may be installed on a shelf or in a slot. It may be adjacent, on one or more sides, to banks of cells that constitute primary battery unit120. To facilitate installation and removal, one or more clamp mechanisms140may be provided to releasably hold unit130in place. To facilitate handling, one or more handles150may also be provided.

Various storage battery technologies are known, that may be suitable for the purposes described here. These include lead-acid, nickel metal hydride, zinc bromine, and lithium-ion battery technologies. Of these various technologies, that currently having the greatest promise may be the lithium-ion battery technology, because it offers a relatively long life cycle, relatively rapid charge time, and relatively high energy density with relatively low weight. For example, Toshiba Corporation has announced a lithium-ion battery with a one-minute charge time to 80% of full capacity, a capacity of 600 mAh in a package of volume less than 90 cc, and a lifetime greater than 1000 charge-discharge cycles.

According to one possible arrangement between the car owner and the utility company, the secondary unit is the property of the utility company. When the car is plugged into the electrical grid, both the primary and secondary battery units are charged. However, the user of the vehicle is only charged for the electricity to charge the primary unit. To further compensate the user for transporting the secondary battery, the cost of the electricity for charging the primary unit may also be made lower than the current market rate.

The utility manages the charge on the secondary battery to limit fluctuations in the power grid. When power is plentiful the secondary batteries on all vehicles connected to the grid are charged. At peak demand, the batteries are discharged. Advantageously, the batteries in cars located near to the demand will be discharged to satisfy the demand minimizing transport loss in the network.

Charging the secondary battery unit can be accomplished with the vehicle charging system or it can simply be swapped, i.e., removed and exchanged for a fully charged battery unit. This provides a secondary benefit to the user. Swapping the secondary battery at a “charging station” will allow for a rapid recharge. Since the charge/discharge rate for the secondary battery might be much larger than a nightly charge for the primary battery, the fact that the battery can be easily replaced is useful, particularly since it might not last as long as the car.

The electric utility reaps a further benefit if it can track and independently manage the charge of the secondary battery. Under current implementations of V2G, the user and the utility compete for control of the battery charge. That is, the user always wants a full battery to have the longest driving range, whereas the utility wants to minimize fluctuations of the grid by partially discharging the battery when advantageous for that purpose. By dividing the battery assembly into a primary unit owned by the user and a secondary unit owned or at least controlled by the utility, the conflict between user and utility is at least partially resolved.

Even greater benefits may be realized if the secondary battery unit is given the ability to communicate its current state of charge, and possibly even its location, to the utility company. From the communicated information, the utility company may plan the times and places for charging or discharging secondary battery units, so as to optimize its load balancing.

Incentives to the user to cooperate in an arrangement as described above include lower prices for electrical power, and the availability of the secondary battery unit to increase the car's range between recharges, at least in emergency situations (although possibly at a higher cost per kwh of electricity).

If communication is enabled between the utility company and the car, the user can be continually updated about the (possibly time-varying) cost for using the secondary battery unit. This aids the user by promoting economically efficient use of the secondary battery unit, and also aids the utility company by affording it greater flexibility in pricing. It should also be noted in this regard that with respect to consumption by the user of the stored energy in the secondary battery unit, the cost of delivery to the point of use is borne by the user, not by the utility company. This provides a further benefit to the utility company.

Shown inFIG. 3is an example of a battery assembly according to the principles described above, and including modules for communication and control. This example is not meant to be limiting, but merely illustrative of one among many possible arrangements useful for achieving the results to be described below. In particular, it should be borne in mind that those functions that involve the processing of data, communications, and other forms of information may be carried out under the control of programs implemented in any combination of hardware, software, and firmware, and may equivalently be carried out by general purpose computers, specialized digital processors, or specialized circuitry. Any and all such implementations should be regarded as equivalents for performing the functions that are to be described.

As seen the figure, a primary battery unit210and a secondary battery unit220are provided. The battery units are connected through switch230to charge/discharge port240, which may, for example, be connected to a utility company's power distribution network through a plug-and-receptacle combination as described above.

Switch230is configured so that under control, it may select one or the other, or both, of battery units210,220for charging or discharging. As noted above, it is advantageous for the total discharge capacity of the secondary unit to be no more than 20% the total discharge capacity of the primary unit. The reason is that if the secondary capacity is substantially more than 20%, the user of the car faces economic inefficiency because he lacks sufficient control over the motive resources of his vehicle.

As noted above, switch230is advantageously configured to selectively draw electric power from one or the other of the primary and secondary battery units, and to independently charge the primary and secondary battery units. In particular, it may be useful for switch230to permit a choice of charging only the primary battery unit, only charging the secondary battery unit, or charging both battery units simultaneously.

Also shown in the figure is Battery Management System (BMS)250. BMS systems have long been used in the art for various functions such as monitoring the state of charge of the batteries and their voltages and current flows, computing battery age indications, balancing the batteries, and protecting the batteries from overcurrents, overvoltages during charging, and undervoltages during discharge. As seen in the figure, BMS250forwards battery state information to controller260and also to outbound communication module310.

With further reference toFIG. 3, controller260controls switch230for charging and discharging the battery units, in response to various inputs which are to be described below. Controller260also forwards information to control panel270for display to the user. The displayed information may include current pricing information for use of the energy stored in the battery units, as well as state information for the battery units.

It should be noted that for discharging a battery unit into the power grid, it will generally be necessary to employ an inverter to convert direct current from the batteries into alternative current that is useable by the power grid. In the example illustrated here, control of the inverter (not shown) is by controller260.

Control panel270provides the user with information about the current state of the battery system, and may also provide account information, for example the cost of electrical energy expended within a specified time period, pricing for the use of the secondary battery unit, the cost of the next recharge, and the like. Those skilled in the art will of course appreciate that the control panel may usefully provide many further types of information to the user.

Control panel270also provides the user with various ways to exert local control over the utilization of the battery units. For example, the user may elect to begin drawing on the secondary battery unit.

Depending on what arrangements have been made with the utility company, the user may also be able to choose among various policies relating to pricing and electrical usage patterns. For example, the costs to the user might depend on whether the user has agreed to recharge only during discount periods, or whether recharging during premium periods is also requested. Similarly, some costs to the user might depend on the extent to which the user wishes to have control over energy storage in the secondary battery unit, or the extent to which the user is willing to cede control to the utility company over energy storage in the primary battery unit.

By using control panel270, the user may be able to select among the various policies, and indicate which should be currently in force. Information about selected policies, and other user-configured information, may be stored in memory280. Communication input module290is configured to receive information from the utility company. As noted, any of various well-known wired or wireless communication technologies may be used to provide connectivity between module290and the utility company. Module290may receive information useful to the user, such as pricing information, and forward it to control panel270for display. Module290may also receive control information from the utility company, and forward it to controller260to be put into effect. Control information may include, for example, instructions (according to the agreed policy) to charge the primary or secondary battery unit, or to discharge (for load balancing in the utility network) the secondary battery unit.

For security, it is desirable to include an authentication module30U that excludes all but authorized entities to exert control of the kind described above. Accordingly, module300, communicating with the remote entity via communication module290, executes any of various well-known authentication protocols. Such protocols may be as simple as checking a password, or as complex as those protocols based on pseudorandom number generation or other cryptographic techniques. In fact, the authentication procedure may be carried out, in part, by a cell phone or other wireless device, which then communicates a permission or denial message to module300.

It should be noted in this regard that although the remote entity that exerts control in this example is the utility company, any of various other remote entities could also be authorized in the same manner. For example, the employees whose cars are parked on the site of a large company could agree that the company may draw on their secondary battery units to help power the company air conditioning system during mid-day periods of high demand.

Communication output module310, as seen in the figure, is configured to transmit battery state information to the utility company. As noted above, it may also be useful to the utility company to be able to track the location of the secondary battery unit. For that purpose, location sensor320, which may for example be a GPS receiver, communicates location information to communication module310.

Communication output module310may also facilitate communication from the user to the utility company by forwarding, for example, the user's currently selected policy. For that purpose, there is a direct or indirect connection from control panel270to module310(omitted from the figure for simplicity of presentation).

When the utility company (or other remote entity) wishes to draw on the charge in the secondary battery unit, it may do so according to the exemplary procedure charted inFIG. 4, to which attention is now directed. At step400, the remote entity detects that an electric drive vehicle is at a location where battery discharge into the power grid is possible. At step410, the remote entity contacts a local controller, such as controller260with a request to begin discharge. At step420, the controller accesses memory280to check the policy currently in force. If the request is consistent with the current policy, the remote entity receives a message that the request is granted. Then, at step430, the remote entity causes switch230to be placed in a state which permits discharge, into the power grid, solely of the secondary battery unit.