METHOD FOR RAPIDLY CHARGING AN ELECTRIC VEHICLE FROM A LIGHT DUTY CHARGING SITE COMPRISING A RESIDENTIAL DWELLING OR A SMALL OFF GRID POWER STATION

Abstract

A fast-charging method is provided for rapidly charging an electric vehicle at a light-duty charging site comprising a residential dwelling or a small off-grid power station. The fast charging method incorporates an intermediate battery bank, or power buffer, that stores energy between EV charging cycles, then discharges the stored energy into the EV at a higher rate than the primary electric power source for the charging system. The power buffer thereby acts as a power multiplier that accelerates the rate of charge of an electric vehicle. Substantial power multiplication factors are possible at light-duty charging sites, resulting in large improvements in electric vehicle charging rates. The method may be applied using a number of primary power sources including AC from the utility grid, DC from photovoltaic panels, or power from other electric vehicle chargers (including both AC and DC electric vehicle chargers).

Claims

1. A method for rapidly charging an electric vehicle from a residential dwelling, the method comprising: providing a primary electric power source at said residential dwelling; providing a power buffer; providing a fast-discharge battery within said power buffer; providing a buffer/load interface; providing an energy storage load within said electric vehicle; providing an electric vehicle battery within said energy storage load; providing means for transmitting power from said primary electric power source at said residential dwelling to said fast-discharge battery within said power buffer; providing means for transmitting power from said fast-discharge battery within said power buffer to said buffer/load interface; providing means for transmitting power from said buffer/load interface to said electric vehicle battery within said energy storage load; transmitting power from said primary electric power source at said residential dwelling to said fast-discharge battery within said power buffer, whereby a power buffer energy may be accumulated in said fast-discharge battery, whereby said power buffer energy may be accumulated and stored in said fast-discharge battery whether or not said electric vehicle is present at said residential dwelling; transmitting power from said fast-discharge battery to said buffer/load interface; transmitting power from said buffer/load interface to said electric vehicle battery within said energy storage load within said electric vehicle, wherein a power buffer energy discharge rate of said power buffer into said buffer/load interface is higher than an energy supply rate of said primary electric power source at said residential dwelling, whereby power from said primary electric power source at said residential dwelling may be multiplied and a charging rate of said electric vehicle may be increased so that said electric vehicle may be rapidly charged from said residential dwelling.

2. The method of claim 1, wherein said primary electric power source comprises a solar photovoltaic power source.

3. The method of claim 1, wherein said fast-discharge battery comprises a lithium-ion battery, wherein said lithium-ion battery may be effective in multiplying power from said primary electric power source, whereby a charging rate of said electric vehicle may be increased.

4. The method of claim 1, wherein said fast discharge battery comprises a solid-state battery, wherein said solid-state battery may be effective in multiplying power from said primary electric power source, whereby a charging rate of said electric vehicle may be increased.

5. The method of claim 1 wherein said fast-discharge battery comprises a used or repurposed rechargeable electric vehicle battery wherein said repurposed rechargeable battery may be effective in multiplying power from said primary electric power source, whereby a charging rate of said electric vehicle may be increased even though said used or repurposed rechargeable battery may not be effective in directly powering an electric vehicle, whereby cost for practicing the method may be reduced and disposal issues for used electric vehicle batteries may be mitigated.

6. The method of claim 1, wherein said means for transmitting power from said buffer/load interface to said electric vehicle battery comprises an inductive coupling means.

7. The method of claim 1, wherein said means for transmitting power from said power buffer to said electric vehicle battery comprises a plug-in cable interconnect, whereby said method may be backward compatible with a large number of common electric vehicles that utilize a plug-in cable connection for charging.

8. The method of claim 1, further including means for converting DC (direct current) from said fast-discharge battery into AC (alternating current), whereby said fast-discharge battery may be used in said residential dwelling for backup AC (alternating current) power, or auxiliary AC (alternating current) power, or supplemental utility grid power, or AC (alternating current) electric vehicle charging power.

9. The method of claim 1, further including means for transporting said fast-discharge battery, whereby said fast-discharge battery may be used for powering an electrical device away from said residential dwelling, whereby said fast-discharge battery may be used to recharge a stranded electric vehicle or provide supplemental power for extending the driving range of an electric vehicle or supply mobile power for charging an electric vehicle where grid power is unavailable or inaccessible.

10. The method of claim 9 wherein said means for transporting said fast-discharge battery comprises a towable trailer on which is mounted said fast-discharge battery.

11. The method of claim 9, further including means for converting DC (direct current) from said fast-discharge battery into AC (alternating current), whereby power may be supplied to electrical devices requiring AC (alternating current), whereby common AC powered equipment, appliances, or power tools may be energized when grid power is unavailable or inaccessible.

12. The method of claim 1, further including means for removing and transporting a portion of said fast-discharge battery, wherein said portion is of a weight that may be transported by a human, whereby said portion of said fast-discharge battery may serve as a convenient and readily deployable light-duty power source.

13. A method for rapidly charging an electric vehicle from a small off-grid power station, the method comprising: providing a primary electric power source comprising a small off-grid power station; providing a power buffer; providing a fast-discharge battery within said power buffer; providing a buffer/load interface; providing an energy storage load within said electric vehicle; providing an electric vehicle battery within said energy storage load; providing means for transmitting power from said small off-grid power station to said power buffer; providing means for transmitting power from said power buffer to said buffer/load interface; providing means for transmitting power from said buffer/load interface to said electric vehicle battery within said energy storage load; energizing said small off-grid power station; transmitting power from said small off-grid power station to said fast-discharge battery within said power buffer, whereby a power buffer energy may be accumulated in said fast-discharge battery, whereby said power buffer energy may be accumulated and stored in said fast-discharge battery whether or not said electric vehicle is present while power is transmitted to said fast-discharge battery from said small off-grid power station; transmitting power from said fast-discharge battery to said buffer/load interface; transmitting power from said buffer/load interface to said electric vehicle battery within said energy storage load within said electric vehicle, wherein a power buffer energy discharge rate of said power buffer is higher than an energy supply rate of said small off-grid power station, whereby power from said small off-grid power station may be multiplied and said electric vehicle may be rapidly charged.

14. The method of claim 13, wherein said electric vehicle is utilized for transport in a military operation, whereby said method for rapidly charging an electric vehicle may improve electric vehicle responsiveness and availability for fast-paced maneuvers and troop transport at a military post.

15. The method of claim 13, wherein said electric vehicle is utilized for transport in an emergency response activity, whereby said method for rapidly charging an electric vehicle may improve electric vehicle responsiveness and availability in a crisis or an emergency.

16. The method of claim 13, wherein said electric vehicle is utilized for transport in a construction activity, whereby said method for rapidly charging an electric vehicle may improve electric vehicle responsiveness and availability for time-sensitive activities at a construction site.

17. The method of claim 13, wherein said electric vehicle is utilized for transport in an outdoor activity, whereby said method for rapidly charging an electric vehicle may improve electric vehicle responsiveness and availability for time-sensitive or fast-paced activities at an outdoor event.

18. A method for rapidly charging an energy storage load onboard an electric vehicle from a light-duty charging site, wherein a power factor during the charging cycle for said energy storage load is less than 0.7, the method comprising: providing a primary electric power source; providing a power buffer connected to said primary electric power source; providing a fast-discharge battery within said power buffer; providing a buffer/load interface connected to said power buffer; providing an energy storage load onboard said electric vehicle; providing means for transmitting power from said power buffer to said buffer/load interface; providing means for transmitting power from said buffer/load interface to said energy storage load onboard said electric vehicle; energizing said primary electric power source; transmitting power from said primary electric power source to said fast-discharge battery within said power buffer, whereby a power buffer energy may be accumulated in said fast-discharge battery, whereby said power buffer energy may be accumulated and stored in said fast-discharge battery whether or not said electric vehicle is present while power is transmitted to said fast-discharge battery from said primary electric power source; charging said energy storage load using said power buffer energy, wherein a power buffer energy discharge rate of said power buffer may be higher than an energy supply rate of said primary electric power source, whereby power from said primary electric power source may be multiplied and said energy storage load onboard said electric vehicle may be rapidly charged.

19. The method of claim 18, wherein said primary electric power source comprises a solar photovoltaic power source, whereby said energy storage load may be rapidly charged using renewable energy with no need for drawing power from a utility grid, whereby power demands on the utility grid may be reduced, especially as large numbers of electric vehicles are manufactured and deployed.

20. The method of claim 18, wherein said primary electric power source comprises a charger for an electric vehicle, whereby said energy storage load may be rapidly charged using existing infrastructure for charging electric vehicles, whereby substantial economies may be realized in rapidly charging said electric vehicle from a large number of existing charging sites and minimal modifications to said existing infrastructure may be needed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] FIG. 1 shows an overall block diagram of the elements of a preferred embodiment of the invention for storing, managing, and ultimately multiplying power from a primary electric power source in a power buffer for the principal purpose of rapidly charging an electric vehicle from a light-duty charging site having low primary power, with optional provisions for supplying backup AC power, returning stored energy to the utility grid, charging an auxiliary battery, and storing energy from a solar photovoltaic panel.

DETAILED DESCRIPTION

[0052] This document discloses a method for rapidly charging EVs in situations where only one or a small number of EVs are typically recharged in a 24-hour period, thereby comprising a limited category of specialized light-duty EV charging applications. In general, the method is practiced by multiplying power from a primary electric power source by utilizing a power buffer so that the charging rate for an energy storage load onboard an EV during an EV charging interval may be increased above the charging rate for the EV at a charger in which charging power is limited to the power level of the primary power source. Limiting the present invention to low EV volumes and light duty is equivalent to limiting the invention to situations in which relatively long idle periods exist between charging cycles. In this situation, substantial energy can be accumulated in a power buffer and the fast-charging rate can then be maximized and/or sustained over relatively long periods of time. Light-duty applications frequently suffer from especially long EV charging durations using prior art EV charging methods, and consequently light-duty applications have considerable need for improvement in EV charging speed.

[0053] More particularly, power may be multiplied in the present invention by first storing energy from a primary power source in an intermediate energy storage device, or power buffer, and then discharging energy stored in the power buffer into an EV battery at a higher rate governed by energy discharge characteristics of the power buffer rather than power flow from the primary power source. In effect, energy from a primary power source is accumulated in the power buffer over a relatively long period of time and then discharged from the power buffer into the EV battery over a relatively short period of time, so that power, which is the amount of energy flow per unit of time, is multiplied and the EV may be rapidly charged. There is no violation of energy conservation since energy is given by the product of power and time and this product is substantially equal during charging and discharging of the power buffer, except for a relatively small energy loss incurred in charging and discharging the power buffer and a small energy loss in storing energy in the power buffer resulting from small leakage currents in the power buffer.

[0054] FIG. 1 shows an overall block diagram of physical elements and physical means needed to practice an embodiment of the inventive method for multiplying power from a primary electric power source in a power buffer for charging an EV from a low-power primary power source. FIG.1 applies, for example, to a fast EV charger at a residential dwelling. Similar physical elements could be applied in a number of alternate situations, including situations in which the primary power source comprises a small off-grid power station comprising a motor generator, or a solar photovoltaic panel, or a wind turbine generator, or some combination of these three power sources. Thus, the present detailed discussion will treat the specialized case of a fast EV charger for a residential dwelling with the understanding that the invention may be used in many other light-duty situations, including fast EV charging from a small off-grid power station, and the invention is limited only by the claims listed at the end of this disclosure.

[0055] With this caveat, there is great need for increased EV charging rates in a residential dwelling due to the relatively low primary power utilized in a residential dwelling for home-based EV charging stations in the prior art, and, therefore, there is great benefit in multiplying the primary power available in a residential dwelling in order to rapidly charge an electric vehicle (EV) and thereby increase the utility and availability of an EV.

[0056] In FIG. 1, principal means for enabling the fast EV charging method of the present invention comprises a fast EV charger 100, with provisions to include the following optional elements that contribute additional functionality beyond fast charging of an EV with minimal additional hardware through the use of shared components: (1) an inverter (Option A) 30 that can provide back-up AC power to AC loads 40 in a residential dwelling (e.g. during a power outage); (2) inverter (Option A) 30 in combination with grid tie 50 for returning excess stored energy in the fast-discharge battery 260 to the utility grid; (3) a detachable battery module (Option B) 20 to provide readily transportable power; and (4) an interface to a solar photovoltaic power source (Option C) 10 or other renewable energy source to add energy to the system in addition to energy supplied by a principal or primary power source.

[0057] In the preferred embodiment, the primary electric power source from which energy originates is provided to the fast EV charger 100 from a relatively low power primary AC power source 110, as commonly supplied by a local utility grid near a residential dwelling. A power buffer 200 is provided outside of an electric vehicle comprising the following elements: (1) RFI/EMI filter 210 that connects to the low power primary AC power source 110 and that reduces radio frequency interference (RFI) and electromagnetic interference (EMI) caused by undesirable frequency components that may be generated in converters 220 and 240 in the power buffer 200; (2) an AC/DC converter 220 connected to the RFI/EMI filter 210; (3) a DC voltage-to-current converter 240 connected to the AC/DC converter 220 that provides a predetermined current profile for effective charging of the fast-discharge battery 260 by means of control signals from feedback link 500; and (4) a fast-discharge battery 260 connected to the DC voltage-to-current converter 240. A buffer/load interface 300 is further provided that conveys power from the power buffer 200 to an EV energy storage load 400.

[0058] While the primary electric power source shown in the embodiment in FIG. 1 is a low power primary AC power source 110, the primary electric power source may alternatively comprise a primary solar photovoltaic power source, which may also be found at a residential dwelling. In this case, there would be no need for elements in the power buffer 200 for converting AC power to DC power (AC/DC converter 220) since the primary solar photovoltaic power source would provide DC directly. A DC voltage-to-current converter 240 would still be required to properly charge the fast-discharge battery 260 from DC supplied by the primary solar photovoltaic panel. In addition, the supplementary solar photovoltaic power source (Option C) would not be required, since the primary solar photovoltaic power source could provide all of the renewable energy for the fast EV charger 100.

[0059] The EV energy storage load 400 is wholly contained onboard an electric vehicle (EV) that is being charged. The EV energy storage load 400 serves as the primary energy source for the EV. As such, the act of charging an EV is synonymous with charging the EV energy storage load 400 within the EV in the present embodiment. The EV energy storage load 400 comprises the following elements: (1) a charge controller 410 connected to the buffer/load interface 300; (2) an EV/charger interface 420 connected to the charge controller 410; and (3) an EV battery 430 connected to the EV/charger interface 420. The charge controller 410 includes an algorithm for adjusting current flow to the energy storage load 400 in a predetermined fashion according to the state-of-charge (SOS) of the EV battery 430 and the condition of the energy storage load 400 as the EV is being charged. The algorithm is designed to minimize charging time, while maintaining safe charging conditions and adequate battery lifetime. For AC coupling to the EV, the charge controller 410 includes elements for rectifying the AC voltages transmitted to the vehicle, and a voltage to current converter for fashioning the charge controller into a current source that generates the predetermined current waveforms needed to charge the EV battery 430. For DC coupling to the EV, the AC rectifier would be eliminated in the charge controller 410. The EV/charger interface 420 provides any buffers or transitions between the charge controller 410 and the EV battery 430, including any general-purpose power busses that may be applied in the EV.

[0060] The buffer/load interface 300 provides power transfer between the power buffer 200 outside the EV and the EV energy storage load 400 inside the EV. In a preferred embodiment, the buffer/load interface 300 may incorporate an electrical wire/cable with a detachable interconnect (plug) that connects directly to the EV. The interconnect design for the invention may copy any of several standard plug designs so that backward compatibility is maintained with a large number of electric vehicles that currently utilize a plug-in connection for EV charging. Power in the form of DC or power-line-like AC (most commonly 50-400 Hz) may be transmitted to the EV using this type of cable interconnect. When DC power is transmitted across the buffer/load interface 300, the buffer/load interface 300 may be directly connected to the charge controller 410 via a plug-in wire connection, or the buffer/load interface 300 may include power conversion circuitry to transform DC voltages from the fast discharge battery 260 in the power buffer 200 into higher or lower voltages compatible with the charge controller 410 in the energy storage buffer 400. Analogously, when power-line-like AC is transmitted across the buffer/load interface 300, the buffer/load interface 300 will include power conversion circuitry to transform DC voltages from the fast-discharge battery 260 into power-line-like AC compatible with the charge controller 410.

[0061] In an alternative embodiment, the buffer/load interface may incorporate a plug-less (wireless) inductive coupling system that transmits AC power to the EV energy storage load 400 at a substantially higher frequency than power-line frequencies. In this case, AC frequencies would extend typically from the kilohertz range to the megahertz range. The buffer/load interface 300 would then include power conversion circuitry for transforming DC power from the fast discharge battery 260 into the high frequency AC power that would be transmitted wirelessly (i.e., without a plug-in connection) to the charge controller 410. In this case, the charge controller 410 would include power conversion circuitry to transform the high frequency AC from the buffer/load interface 300 offboard the EV into DC that is suitable for charging the EV battery 430 via the EV/charger interface 420.

[0062] In each specific implementation, information on the SOC (state-of-charge) of the EV battery 430, energy usage of the EV, and other data related to general performance and status is transmitted from the energy storage load 400 to the buffer/load interface 300 via EV/charger communication link 600. From there, the EV/charger communication link 600 provides to a master control system information related to EV system parameters and overall charging system status onboard the EV.

[0063] The low power primary AC power source 110 typically supplies energy at a nominal 120 Volts 60 Hz single-phase AC or a nominal 240 Volts 60 Hz two-phase AC in a residential dwelling in the United States. Other voltages and AC frequencies that are customary in other countries around the world may also be used with the invention. Common current levels for a dwelling in the United States range from 100-200 Amps rms (root mean squared). While it is therefore possible, in principle, to supply as much as 24 kW from 100 Amp, 240 Volt electric service, or 48 kW from 240 Volt 200 Amp service, much less power is used in practice for charging an electric automobile at a residential dwelling, partially because much of the power in a dwelling must be reserved for other loads in and around the home. In fact, present standard practice utilizes standardized Level 1 or Level 2 chargers for charging an electric automobile in a residential dwelling. These standard chargers typically operate well below maximum input service ratings for a residential dwelling.

[0064] For example, Level 1 chargers have a maximum power rating of 1.9 kW, while Level 2 chargers have a maximum power rating of 19.2 kW. Level 1 chargers may be plugged into an ordinary 120 Volt, 20 Amp outlet in a home, but about 21 hours will be required to recharge a depleted 50 kW-hr battery in an EV to 80% capacity. A Level 2 charger utilizes the 240 Volt service in a dwelling at 18-80 Amps of current. A Level 2 charger operating at maximum output could bring a depleted 50 kW-hr EV battery to 80% capacity in 2.6 hours. While a Level 2 charger has a maximum power rating of 19.2 kW, power levels of less than 7 kW are more typically applied in a residential dwelling. At 7 kW, a depleted 50 kW-hr EV battery would be recharged to 80% capacity (40 kW-hrs.) in about 5.7 hours. These long recharging times using current practice in a residential dwelling are inconvenient and undesirable. In an emergency situation, for example a situation requiring critical medical care, long recharging times may even put lives at risk when immediate transport to a medical center is needed.

[0065] Long charging times of conventional EV charging methods in a residential dwelling will be mitigated by the present invention since energy stored in the fast-discharge battery 260 of the power buffer 200 may be applied to the EV battery 430 in the EV energy storage load 400 at a substantially increased charging rate, governed by the energy discharge characteristics of the fast-discharge battery 260 rather than the more limited peak power rating of the low power primary AC power source 110.

[0066] For example, using one of the many types of fast-discharge batteries that are commercially available in place of the fast-discharge battery 260 in the embodiment in FIG.1, such as the Sib lithium-ion rechargeable battery manufactured by Toshiba, energy stored in the power buffer 200 may be discharged into the EV energy storage load 400 in as little as six minutes. Discharging 40 kW-hrs. of energy stored in the power buffer 200 into the EV energy storage load 400 in six minutes is equivalent to charging the EV energy storage load 400 at a power level of 400 kW, which is twenty-one times faster than EV charging from a Level 2 charger at maximum power (19.2 kW). Even if all of the available AC power in a residential dwelling could be used for direct EV charging by conventional means, which leaves no power for other household loads and heavily taxes utility services, the 400 kW equivalent power of the present method would still charge an EV over eight times faster than the maximum conventional charging rate at the highest voltage (240V) and current (200 Amps) typically available in a residential dwelling.

[0067] In principle, the invention can be applied using any rechargeable battery that has a discharge power capacity greater than the primary electric power level. The various types of lithium-ion batteries with liquid electrolytes fall into this category. Of particular interest, lithium titanate oxide (LTO) batteries can be discharged at rates in excess of 10 C (discharge current ten times the current used in the one-hour battery capacity rating), making it possible to charge compatible EV batteries in as little as six minutes. The Toshiba battery mentioned above falls into this category of rechargeable LTO lithium-ion battery chemistries.

[0068] Other battery types that may provide very high discharge rates beneficial to the invention include solid-state batteries, vertically-aligned carbon nanotube batteries, lithium-sulfur batteries, graphene batteries, aluminum-air batteries, dual-carbon batteries, sodium-ion, aluminum-ion, and carbon-ion batteries, and super-capacitor-like batteries. Of these alternative battery types, solid-state batteries show great promise for power multiplication in the present invention. Solid-state batteries are commonly considered a type of lithium-ion battery that replaces the liquid electrolyte with a solid electrolyte, resulting in improvements in energy density and charge/discharge rate.

[0069] As an important feature of the present invention, energy is applied to the power buffer 200 in a residential dwelling on a schedule that is largely independent of the EV schedule. In particular, the EV and its associated EV battery 430 do not need to be present while energy is accumulated in the power buffer 200. Energy can then be accumulated in the power buffer 200 on a very flexible schedule at any selected interval throughout the day or night as determined by the EV owner. Since the power buffer 200 enables fast EV charging that only requires vehicle presence over a substantially reduced time interval, the EV battery 430 may be charged on a very flexible schedule at almost any time during the day or night.

[0070] System elements of the fast EV charger 100 needed for charging the EV battery 430 can serve multiple functions in a residential dwelling that would not be found at a single-purpose public charging station. For example, to service the wide variety of electrical loads in a residential dwelling, energy stored in the power buffer 200 could be used to provide backup power for a residential dwelling by converting DC power from the fast charge battery 260 into 60 Hz AC power in the optional inverter 30 connected to the fast charge battery 260. Backup power could then be used to supply energy to a residential dwelling during power outages in addition to supplying energy to an EV. For example, 50 kW-hrs. of energy storage in the fast-charge battery 260 of the power buffer 200 could supply a relatively high demand level of 5 kW to a residential dwelling for ten hours during a power outage on the utility grid, effectively eliminating the need for a separate motorized backup generator. Excess energy may also be returned to the utility grid by means of inverter 30 and grid tie 50. Power transmission back to the utility grid will enable the sale of excess energy to the utility company in a process known commonly as “net metering.”

[0071] In a further optional function of the fast EV charger 100, energy from a renewable energy source, such as a solar photovoltaic power source 10, may be added to the energy supplied to the fast-discharge battery 260 by the low-power primary AC power source 110. In this case, the solar photovoltaic power source 10 would tap into the DC voltage-to-current converter 240 to control charging of the fast-discharge battery from the solar photovoltaic power source 10. Existing elements of the fast EV charger 100 required for fast EV charging may then be utilized to convey energy from the solar photovoltaic power source 10 to the EV battery 430 and/or AC loads 40 via inverter 30. Alternatively, energy from the solar photovoltaic power source may be conveyed to the utility grid via inverter 30 in combination with grid tie 50. Thus, equipment inherent in the fast-charger 100 provides all of the auxiliary power conversion and transmission equipment needed for a complete solar photovoltaic power station and energy delivery system using pre-existing hardware already in place for fast EV charging. The only additional elements needed to implement a complete solar photovoltaic power generation and delivery system are the solar photovoltaic cells.

[0072] It should be understood that while the preferred embodiment comprises a method for rapidly charging an EV using limited AC power at a residential dwelling, the method can be applied to any light-duty EV charging situation in which the primary AC power is relatively low and there is great need for increasing EV charging rates. In particular, functional block diagrams similar to FIG. 1 would apply in many under-served situations where a relatively low power AC power source may be all that is available. For example, as pointed out previously in this disclosure, relatively low primary power can be found at shared public charging stations in the form of standard Level 1 and Level 2 chargers. In this case, the method could be applied to existing public charging stations by providing a retrofit power boost system at these sites.

[0073] It has also been pointed out in this disclosure that the method can be applied to great advantage at any EV charging site supplied by a relatively small off-grid power station (e.g., less than about 50 kilowatts) in which primary electric power is supplied by a motor-driven generator, or a solar photovoltaic panel, or a wind turbine generator, or a combination of these three power sources. Specific EV charging sites that would typically utilize a small off-grid power station under this broad category include military bases, disaster relief sites, construction areas, and special outdoor events.

[0074] It should be understood that the method is not limited to multiplying power from an AC power source in order to increase EV charging rates. Rather, the method can utilize a DC primary power source in place of the primary AC power source, as would be the case when the primary power source comprises a photovoltaic panel, as already mentioned, or a primary DC (direct current) EV charger, wind turbine DC generator, or other DC power supply.

[0075] It should also be understood that the method applies not only to EV charging sites that have relatively low primary power and associated light-duty EV use, but also to sites that have high primary power yet low EV use. The common element in all cases is the limitation of light-duty EV charging where only a small number of EVs may be charged in a 24-hour period and substantial energy may be accumulated in a power buffer between charging cycles so that large power and long power duration can be established during the EV charging cycle. Charging rates at many light-duty EV charging sites are typically very low using prior art methods. As a result, there has been an acute and long-standing need to increase EV charging rates for improved utility of EVs at typical light-duty charging sites, including residential dwellings and small off-grid power stations.

[0076] It should also be clear that the invention can be practiced not only to increase the charging rate of electric automobiles in light-duty situations, but the invention can be practiced advantageously to increase the charging rates of other electric vehicles, including light-duty electric trucks, electric bicycles, electric motor scooters, electric motorcycles, electric carts (e.g., electric golf carts, recreational carts, and utility carts), and electric fork-lift trucks. The term “electric vehicle” used in the following claims is to be interpreted in this broader sense. With these caveats, implementations of the invention are covered by the following claims