System and method for plug-in vehicle to plug-in vehicle charging

Abstract

A station constituted of: a control circuit; a first and a second bi-directional converter, each in communication with the control circuit, each arranged to be coupled to a respective plug-in electrical vehicle at a respective first port thereof; and a connection to an AC grid, wherein the control circuit is arranged to: draw electrical energy from a first plug-in electrical vehicle coupled to the first port of the first bi-directional converter; and provide at least some of the drawn electrical energy to a second plug-in electrical vehicle coupled to the first port of the second bi-directional converter.

Claims

1. A station comprising: a control circuit; a first and a second bi-directional converter, each in communication with the control circuit, each arranged to be coupled to a respective plug-in electrical vehicle at a respective first port thereof, each having a commonly coupled respective second port; and a connection to an AC grid, wherein the control circuit is arranged to: draw electrical energy from a first plug-in electrical vehicle coupled to the first port of the first bi-directional converter; and provide at least some of the drawn electrical energy to a second plug-in electrical vehicle coupled to the first port of the second bi-directional converter, wherein in the event that an amount of electrical energy drawn from the first plug-in electrical vehicle is greater than an amount of electrical energy provided to the second plug-in electrical vehicle, the control circuit is arranged to provide a difference in the electrical energy to the AC grid.

2. The station of claim 1, wherein in the event that the amount of electrical energy drawn from the first plug-in electrical vehicle is less than the amount of electrical energy provided to the second plug-in electrical vehicle, the control circuit is arranged to provide a difference in the electrical energy from the AC grid.

3. The station of claim 2, wherein the amount of electrical energy drawn from the first plug-in electrical vehicle is measured at the commonly coupled second port of the first bi-directional converter, and wherein the amount of electrical energy provided to the second plug-in electrical vehicle is measured at the commonly coupled second port of the second bi-directional converter.

4. The station of claim 3, wherein the amount of electrical energy drawn from the first plug-in electrical vehicle is measured by a respective current sensor, and wherein the amount of electrical energy provided to the second plug-in electrical vehicle is measured by a respective current sensor.

5. The station of claim 1, wherein the amount of electrical energy drawn from the first plug-in electrical vehicle is measured at the commonly coupled second port of the first bi-directional converter, and wherein the amount of electrical energy provided to the second plug-in electrical vehicle is measured at the commonly coupled second port of the second bi-directional converter.

6. The station of claim 5, wherein the amount of electrical energy drawn from the first plug-in electrical vehicle is measured by a respective current sensor, and wherein the amount of electrical energy provided to the second plug-in electrical vehicle is measured by a respective current sensor.

7. A station comprising: a control circuit; a first and a second bi-directional converter, each in communication with the control circuit, each arranged to be coupled to a respective plug-in electrical vehicle at a respective first port thereof, each having a commonly coupled respective second port; and a connection to an AC grid, wherein the control circuit is arranged to: draw electrical energy from a first plug-in electrical vehicle coupled to the first port of the first bi-directional converter; and provide at least some of the drawn electrical energy to a second plug-in electrical vehicle coupled to the first port of the second bi-directional converter, wherein in the event that an amount of electrical energy drawn from the first plug-in electrical vehicle is less than an amount of electrical energy provided to the second plug-in electrical vehicle, the control circuit is arranged to provide a difference in the electrical energy from the AC grid.

8. The station of claim 7, wherein in the event that the amount of electrical energy drawn from the first plug-in electrical vehicle is greater than the amount of electrical energy provided to the second plug-in electrical vehicle, the control circuit is arranged to provide a difference in the electrical energy to the AC grid.

9. The station of claim 8, wherein the amount of electrical energy drawn from the first plug-in electrical vehicle is measured at the commonly coupled second port of the first bi-directional converter, and wherein the amount of electrical energy provided to the second plug-in electrical vehicle is measured at the commonly coupled second port of the second bi-directional converter.

10. The station of claim 9, wherein the amount of electrical energy drawn from the first plug-in electrical vehicle is measured by a respective current sensor, and wherein the amount of electrical energy provided to the second plug-in electrical vehicle is measured by a respective current sensor.

11. The station of claim 7, wherein the amount of electrical energy drawn from the first plug-in electrical vehicle is measured at the commonly coupled second port of the first bi-directional converter, and wherein the amount of electrical energy provided to the second plug-in electrical vehicle is measured at the commonly coupled second port of the second bi-directional converter.

12. The station of claim 11, wherein the amount of electrical energy drawn from the first plug-in electrical vehicle is measured by a respective current sensor, and wherein the amount of electrical energy provided to the second plug-in electrical vehicle is measured by a respective current sensor.

13. A method of providing electrical energy to a plug-in electrical vehicle comprising: drawing electrical energy from a first plug-in electrical vehicle coupled to a first port of a first bi-directional converter; providing at least some of the drawn electrical energy to a second plug-in electrical vehicle coupled to a first port of a second bi-directional converter, each of the first bi-directional converter and the second bi-directional converter having a commonly coupled respective second port; and in the event that an amount of the electrical energy drawn from the first plug-in electrical vehicle is greater than an amount of electrical energy provided to the second plug-in electrical vehicle, providing a difference in the electrical energy to a coupled AC grid.

14. The method of claim 13, wherein in the event that the amount of electrical energy drawn from the first plug-in electrical vehicle is less than the amount of electrical energy provided to the second plug-in electrical vehicle, providing a difference in the electrical energy from the coupled AC grid.

15. The method of claim 14, wherein the amount of electrical energy drawn from the first plug-in electrical vehicle is measured at the commonly coupled second port of the first bi-directional converter, and wherein the amount of electrical energy provided to the second plug-in electrical vehicle is measured at the commonly coupled second port of the second bi-directional converter.

16. The method of claim 15, wherein the amount of electrical energy drawn from the first plug-in electrical vehicle is measured by a respective current sensor, and wherein the amount of electrical energy provided to the second plug-in electrical vehicle is measured by a respective current sensor.

17. The method of claim 13, wherein the amount of electrical energy drawn from the first plug-in electrical vehicle is measured at the commonly coupled second port of the first bi-directional converter, and wherein the amount of electrical energy provided to the second plug-in electrical vehicle is measured at the commonly coupled second port of the second bi-directional converter.

18. The method of claim 17, wherein the amount of electrical energy drawn from the first plug-in electrical vehicle is measured by a respective current sensor, and wherein the amount of electrical energy provided to the second plug-in electrical vehicle is measured by a respective current sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings in which like numerals designate corresponding elements or sections throughout.

(2) With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. In the accompanying drawings:

(3) FIG. 1A illustrates a high level block diagram of an embodiment of an electric vehicle fast charging station coupled to an AC grid via a bi-directional AC/DC converter, where an electrical vehicle is charged via a DC/DC charger;

(4) FIG. 1B illustrates a high level block diagram of an embodiment of an electric vehicle fast charging station coupled to an AC grid via a bi-directional AC/DC converter, where an electrical vehicle is charged via an AC/DC charger;

(5) FIG. 1C illustrates further details of an implementation of the electric vehicle fast charging station of FIG. 1B;

(6) FIG. 2A illustrates a graph of the efficiency a flywheel embodiment of an electrical storage unit, as a function of power flow to/from the flywheel electrical storage unit;

(7) FIG. 2B illustrates a graph of maximum power available from a flywheel embodiment of an electrical storage unit as a function of the state of charge;

(8) FIG. 3 illustrates a high level flow chart of the operation of a control circuit of any of the embodiments of FIGS. 1A-1C of a method of off-line optimization;

(9) FIG. 4 illustrates a high level flow chart of the operation of a control circuit of any of the embodiments of FIGS. 1A-1C to provide electrical power to either the AC grid or to PEVs;

(10) FIG. 5 illustrates a high level flow chart of the operation of a control circuit of any of the embodiments of FIGS. 1A-1C to draw electrical power from the AC grid while its PEV charging demand is less than a contracted draw amount;

(11) FIG. 6 illustrates a high level flow chart of the operation of a control circuit of any of the embodiments of FIGS. 1A-1C to maintain the electrical power drawn from the AC grid within a predetermined range;

(12) FIG. 7A illustrates a high level block diagram of an embodiment of an electric vehicle fast charging station coupled to an AC grid via a bi-directional AC/DC converter, where a first electrical vehicle is arranged to charge a second electrical vehicle; and

(13) FIG. 7B illustrates a high level flow chart of a method of operation of the arrangement of FIG. 7A to provide plug-in vehicle to plug-in vehicle charging.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(14) Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is applicable to other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

(15) The embodiments are particularly described in relation to a fast charging station, particularly and EVFCS, however this is not meant to be limiting in any way. The embodiments are equally applicable for an energy storage station for use in connection with an alternating current (AC) grid having a load, whose energy consumption varies over time.

(16) FIG. 1A illustrates a high level block diagram of an embodiment of an EVFCS 10 arranged to provide a fast charge for a plug-in electric vehicle (PEV) 80, EVFCS 10 is coupled to an AC grid 15 via a bi-directional AC/DC converter 40 and in communication with a DSO 20. While a single bi-directional AC/DC converter 40 is illustrated, this is not meant to be limiting in any way, and a plurality of bi-directional AC/DC converters 40 may be provided, operating in parallel, without exceeding the scope. EVFCS 10 comprises: a control circuit 30; a power sensor 35; a bi-directional AC/DC converter 40; a plurality of electrical storage units 50; a plurality of current sensors 55; a DC bus 60; a voltage sensor 65; and a plurality of DC/DC charging units 70. Each electrical storage unit 50 may be constituted of magnetically coupled flywheel, without limitation, and as will be described further below may incorporate a servo amplifier in communication with a motor/generator. Each electrical storage unit 50 may have a power converter associated therewith, and optionally a local controller, as known to those skilled in the art (not shown for simplicity) and incorporate a respective current sensor 55. Each DC/DC charging unit 70 has a respective current sensor 55 associated therewith, and bi-directional AC/DC converter 40 has a respective current sensor 55 associated therewith arranged to sense the current flow to/from DC bus 60. DSO 20 is in bidirectional communication with control circuit 30, either over a dedicated connection, or via an Internet link. Control circuit 30 is in communication with: power sensor 35; bi-directional AC/DC converter 40; each electrical storage unit 50; each current sensor 55, voltage sensor 65; and each DC/DC charging unit 70; the connections not shown for simplicity. DC bus 60 connects each of electrical storage units 50, DC/DC charging units 70 and bi-directional AC/DC converter 40. Bi-directional AC/DC converter 40 is coupled to AC grid 15, a relevant portion of which is supervised by DSO 20. Each DC/DC charging unit 70 is arranged to couple to a PEV 80 and provide a fast charge for the coupled PEV 80. Power sensor 35 is arranged to sense the total power flowing to/from AC grid 15 to/from EVFCS 10, and may be incorporated within bidirectional AC/DC converter 40. Voltage sensor 65 is arranged to detect the voltage level of DC bus 60. Each current sensor 55 associated with a respective electrical storage unit 50 is arranged to sense the amount of current flowing to/from the respective electrical storage unit 50; and each current sensor 55 associated with a respective DC/DC charger 70 is arranged to sense the amount of current flowing to/from the respective DC/DC charger 70. Current sensors 55 may be implemented by Hall effect sensors, fluxgate transformer, sense resistor or a fiber optic current sensor without exceeding the scope.

(17) Power sensor 35 may be implemented by Hall effect sensors, fluxgate transformer, Rogowski coil, current clamp meter, sense resistor or a fiber optic current sensor, in combination with a voltage sensor, without exceeding the scope. Power sensor 35 may be comprised of a plurality of subsensors each arranged for an associated phase of a 3 phase connection. Voltage sensor 65 may be implemented with an analog to digital converter. In one non-limiting embodiment power sensor 35 is implemented by a commercially available power meter model PM135 EH available from SATEC, Ltd., Jerusalem, Israel.

(18) Control circuit 30 may be implemented by a microcontroller, field programmable gate area, computer, or application specific integrated circuit, or a combination of such elements without exceeding the scope. Methods of operation described herein may be performed by control circuit 30 responsive to electronically readable instructions stored on an associated memory.

(19) FIG. 1B illustrates a high level block diagram of an embodiment of an EVFCS 100 arranged to provide a fast charge for a PEV 80, where EVFCS 100 is coupled to AC grid 15 via a bi-directional AC/DC converter 40 and in communication with a DSO 20. While a single bi-directional AC/DC converter 40 is illustrated, this is not meant to be limiting in any way, and a plurality of bi-directional AC/DC converters 40 may be provided, operating in parallel, without exceeding the scope. EVFCS 100 comprises: control circuit 30; a plurality of power sensors 35; a bi-directional AC/DC converter 40; a plurality of electrical storage units 50; a plurality of current sensors 55; a DC bus 60; a voltage sensor 65; and a plurality of AC/DC charging units 130. In one non-limiting embodiment each power sensor 35 is implemented by a commercially available power meter model PM135 EH available from SATEC, Ltd., Jerusalem, Israel. Each electrical storage unit 50 may be constituted of magnetically coupled flywheel, without limitation, and as will be described further below may incorporate a servo amplifier in communication with a motor/generator. Each electrical storage unit 50 may have a power converter associated therewith, and optionally a local controller, as known to those skilled in the art (not shown for simplicity) and incorporate a respective current sensor 55. AC grid 15 has a respective power sensor 35 associated therewith, and bi-directional AC/DC converter 40 has a respective power sensor 35 associated therewith and a respective current sensor 55 associated therewith arranged to sense the current flow to/from DC bus 60. DSO 20 is in bidirectional communication with control circuit 30, either over a dedicated connection, or via an Internet link. Control circuit 30 is in communication with: each power sensor 35; bi-directional AC/DC converter 40; each electrical storage unit 50; each current sensor 55, voltage sensor 65; and each AC/DC charging unit 130, the connections not shown for simplicity. DC bus 60 connects each of electrical storage units 50 to bi-directional AC/DC converter 40. Bi-directional AC/DC converter 40 is coupled to AC grid 15, a relevant portion of which is supervised by DSO 20. Each AC/DC charging unit 130 is coupled to the AC side of bi-directional AC/DC converter 40 at a common node 38, and arranged to couple to a PEV 80 and provide a fast charge for the coupled PEV 80. The power sensor 35 associated with AC grid 15 is advantageously coupled between AC grid 15 and common node 38 so as to sense power coming to/from AC grid 15 to/from EVFCS 100. The power sensor 35 associated with bi-directional AC/DC converter 40 is coupled between common node 38 and the AC side of bi-directional AC/DC converter 40 and provides information regarding the amount of AC power input/output by AC/DC converter 40.

(20) FIG. 1C illustrates a high level block diagram of an embodiment of a system 200 utilizing the EVFCS 100 in cooperation with a remote control center 220, further highlighting certain aspects of communication and control in EVFCS 100. System 200 is illustrated comprising EVFCS 100, however this is not meant to be limiting in any way, and EVFCS 100 may be replaced by a station comprising one or more electrical storage units, coupled to an AC grid, with a local load, or a coupleable connection to a load, the electrical energy consumption of which load varies over time, without exceeding the scope. The communication path between control circuit 30 and each power sensor 35; bi-directional AC/DC converter 40; each electrical storage unit 50; each current sensor 55, voltage sensor 65; and each AC/DC charging unit 130 is illustrated with a dot-dash line. An optional connection to AC/DC charging unit 130 is further shown. Each electrical storage unit 50 is illustrated as comprised of a DC/AC converter 230 in communication with a respective motor/generator 240. Control circuit 30 is in communication with each of DSO 20 and remote control center 220 via a communication cloud 210.

(21) In one embodiment, motor/generator 240 is comprised of an annular stator mounted outside a flywheel vacuum chamber, and a vacuum barrier cup housing a motor rotor which motor rotor is mounted on top of a flywheel shaft within the flywheel vacuum chamber. The motor rotor is magnetically coupled to the stator via the vacuum barrier cup as described in the aforementioned International Application Publication WO2014/020593. DC/AC converter 230 may be implemented in a servo-amplifier, such as those sold by Servotronix of Petach Tikva, Israel, and may incorporate therein the respective current sensor 55 (not shown). Bi-directional AD/DC converter 40 may be implemented by a converter sold by SolarEdge Technologies, Inc., of Freemont, Calif., and may comprise therein the respective current sensor 55 and power sensor 35. Remote control center 220 provides for remote control of multiple EVFCS 100 from a single control location.

(22) In order to provide a fast charge to a random number of PEVs 80, without disturbing the AC grid by presenting sharply varying loads, each of EVFCS 10 and EVFCS 100 stores electrical energy in electrical storage units 50 whenever the demand from PEVs 80 coupled thereto is less than a predetermined amount, thus providing a fixed load to AC grid 15. Advantageously, by providing a bi-directional conversion between AC grid 15 and EVFCS 10, 100 power may be provided from EVFCS 10, 100 to AC grid 15, when AC grid 15 is experiencing a temporary over-demand condition.

(23) In order to efficiently operate EVFCS 10, 100, the storage abilities of the selected electrical storage unit 50 were analyzed by the inventors. FIG. 2A illustrates a graph of the efficiency a flywheel embodiment of an electrical storage unit, as a function of power flow to/from the flywheel electrical storage unit 50, wherein the x-axis illustrates power being drawn from, or provided to, electrical storage unit 50 as a percentage of a maximum amount of power which may be handled by electrical storage unit 50 and the y-axis illustrates efficiency of the motor plus driver of such flywheel as a percentage of a theoretical maximum efficiency. As a can be seen efficiency increases monotonically with power level, with efficiency of above 80% experienced down to a power level of about 30%. Below about 20% of the maximum power level efficiency drops off rapidly.

(24) FIG. 2B illustrates a graph of maximum power available from each flywheel electrical storage unit 50 as a function of the state of charge, where the x-axis represents the state of charge of the device in percentage of maximum and the y-axis represents the maximal available power as a percentage of the total available power. Thus as the state of charge of each flywheel electrical storage unit 50 increases, the amount of power available increases. State of charge of a flywheel is a function of the rotational speed and thus can be easily monitored. As a can be seen maximum available power increases monotonically with increasing state of charge, with a sharp drop off when the state of charge falls below about 10%. As the flywheel discharges its ability to deliver power decreases due to the fact that the power is linearly dependent on the EMF voltage of the motor, which itself is linearly dependent on the speed of the flywheel. The speed of the flywheel also relates to the remaining capacity of the flywheel. In certain embodiments, the energy storage capacity of flywheel electrical storage unit 50 is 3 KWH, and the maximum power is 15 KW.

(25) As can be seen from FIG. 2A however, high efficiency is achieved by drawing power near the maximum available power from each flywheel electrical storage unit 50. Thus, utilizing power from multiple flywheel electrical storage units 50 by simply dividing the total required power equally among the flywheel electrical storage units 50 results in an inefficient solution.

(26) As indicated above, EVFCS 10, 100 are bidirectionally coupled to AC grid 15, and in bidirectional communication with DSO 20. In the event that DSO 20 experiences a demand in excess of plan, DSO 20 preferably send a request for a predetermined amount of power to control circuitry 30. Control circuitry 30 must balance the request from DSO 20 with the potential demand from PEV 80, which is unrelated to demand from DSO 20. Remote control center 220 is operative to manage demands over a plurality of EVFCSs 10, 100 so as to achieve an improved financial result. It is to be noted that a demand from DSO 20 is however preferably treated as a high priority, since in certain situations the financial rewards for supplying DSO 20 are significantly greater, pre KWH, than the rewards for charging PEV 20.

(27) EVFCS 10, 100 is faced with 2 different, uncorrelated demands: the demand from PEVs 80; and any request from DSO 20. As indicated above, the demand from PEVs 80, which are coupleable to EVFCS 10, 100, vary over time. Mathematically, the total amount of electrical storage available at EVFSC 10, 100, as a function of time, may be split among: a percentage reserved for PEVs 80, denoted as C %(t); an amount reserved to supply requests from DSO 20, denoted as BC.sub.charge %(t) and an additional amount reserved for energy absorption from AC grid 15 responsive to requests from DSO 20, denoted as BC.sub.discharge %(t). The sum of the 3 terms: C %(t), BC.sub.charge %(t); and BC.sub.discharge %(t) for any given time (t) is 100%. The above amounts are allocated values and not necessarily utilized, or available, values. For example, in the event that we have allocated 70% for C %(t), this means that the system controller 30 can use up to 70% of the total energy capacity of EVFSC 10, 100 for the purpose of EV charging. When the charging is completed it is clear that the 70% is not available any more until the unit is recharged, but the allocation remains unchanged.

(28) In order to determine the optimal response to such a situation, we minimize the value of unmet opportunities which can be expressed as:
USSR(t)=A(t).Math.ΣE.sub.BCcharge.Math.(1−SL.sub.BCS)+B(t).Math.ΣE.sub.ev.Math.(1−SL.sub.ECV)+C(t).Math.ΣE.sub.BCdischarge.Math.(1−SL.sub.ECV)  EQ. 1
where:
A(t) is the economic value of supplying requests from DSO 20, which may be expressed in Euro/kWh;
E.sub.BC is the energy requested by all connected DSOs 20 which may be expressed in kWh;
SL.sub.BCS is the fraction of the total E.sub.BC that was met by the individual EVFCS 10, 100;
B(t) is the economic value of supplying requests from the arriving PEVs 80, which may be expressed in Euro/kWh;
E.sub.ev is the energy requested by the arriving PEVs 80 which may be expressed in kWh; and
SL.sub.ECV is the fraction of the total E.sub.ev that was met by the individual EVFCS 10, 100;
C(t) is the economic value of supplying requests from DSO 20 to absorb energy, which may be expressed in Euro/kWh;
E.sub.BCdischarge is the energy absorption request by DSO 20, which may be expressed in kWh; and
SL.sub.BCS is the fraction of the total E.sub.BCdischarge that was met by the individual unit 10,100.
EQ. 1 defines a value for unmet demand, and thus minimizing the equation provides an optimal economic value.

(29) In one embodiment, as illustrated in FIG. 3, off-line optimization is performed by control circuit 30. In state 1000, a history is logged, and divided into predetermined time slots. In stage 1010, for each historical time slot, the value of USSR is calculated for an array of values of C %(t) and BC.sub.charge %(t) and BC.sub.discharge %(t). In stage 1020 the minimal value for USSR for the historical time slot is calculated, and used as a starting point for a steepest decent optimization algorithm to find the optimal value. In optional stage 1030, the above is repeated for separately for weekdays, weekends, holidays and over the various seasons. In stage 1040, the chart of stage 1020-1030 is stored and utilized going forward to allocate energy responsive to demand from DSO 20 and PEVs 80. Thus, 100% of the stored energy capacity of EVFCSs 10,100 is allocated in accordance with an expected maximal economic value between DSO 20 and PEVs 80.

(30) The above has been described in an embodiment where no limitations are provided to C %(t) and BC.sub.charge %(t) and BC.sub.discharge %(t), however this is not meant to be limiting in any way. In another embodiment each of C %(t) and BC.sub.charge %(t) and BC.sub.discharge %(t) are limited to only allow a predetermined range of acceptable values, as illustrated in optional stage 1050. Such a limitation will prevent allocation of energy to DSO 20 to the exclusion of PEV 80. As indicated above, the above has been particularly described in relation to an EVFCS, however this is not meant to be limiting in any way. EVFCS may be replaced by a station comprising one or more electrical storage units, coupled to an AC grid, with a local load, or a coupleable connection to a load, the electrical energy consumption of which load varies over time, without exceeding the scope.

(31) Referring back to FIGS. 2A, 2B, the inventors have realized that in order to efficiently support a load with a plurality of flywheel based electrical storage units 50, it is important to maintain a high percentage power load to each electrical storage unit 50. Thus, simply dividing any demand equally among flywheel based electrical storage units 50 results in a suboptimal solution.

(32) FIG. 4 illustrates a high level flow chart of the operation of control circuit 30 of a station, to provide electrical energy from the plurality of flywheel based electrical storage units 50 to either AC grid 15, responsive to a request from DSO 20, or to PEVs 80 through DC/DC charging units 70, or AC/DC charging units 130, respectively, PEVs 80 representing an embodiment of a couplable time varying load. In stage 2000 a request for power is received by control circuit 30 with an associated maximum amount of ripple, with the request power denoted “Preq”, and the maximum amount of ripple denoted “ΔP”. Preq may be either positive or negative value, depending if we need to perform charging or discharging of the flywheel based electrical storage units 50. ΔP may be predetermined for the system, or may be supplied along with the request, without limitation. Different ripple amounts may be utilized for each demand, for example through DC/DC charging units 70, or AC/DC charging units 130, respectively may have a first maximum ripple amount associated therewith and AC grid 15 may have a different ripple amount associated therewith. A timer is further set to ensure that the operation of FIG. 4 is repeated regularly during operation. In one embodiment, the timer of stage 2000 is set to 1 minute.

(33) In stage 2010, all of the flywheel based electrical storage units 50 are scanned to determine the presently available maximum power available from each of the N associated flywheel based electrical storage units 50. Mathematically, for a flywheel based electrical storage unit 50, the maximum amount of available power from flywheel “j” at a specific point in time is determined as:
Pmax.sub.j=Imax.sub.j*Ke.sub.j*ω.sub.j*0.87  EQ. 2
Where Imax.sub.j is the maximal peak current value for flywheel “j’, Ke.sub.j is the motor generator EMF constant for flywheel “j” and ω.sub.j is the present flywheel speed in RPM for flywheel “j”. Thus, Pmax.sub.j varies with ω.sub.j since for a given flywheel based electrical storage unit 50, since both Imax.sub.j and Ke.sub.j are constant.

(34) In stage 2020, the flywheels are sorted in descending order of power. It is to be understood that stage 2020 is not strictly required, and is described herein for ease of understanding. In stage 2030, M+1 flywheel based electrical storage units 50 are selected in descending order of power, such that:
Σ.sub.1.sup.M+1Pmax.sub.j≥Preq>Σ.sub.1.sup.MPmax.sub.j  EQ. 3

(35) It is to be understood from EQ. 3 that M flywheels are being selected to operate at their respective Pmax, and flywheel M+1 may operate at less than Pmax. The current required from each of the M+1 selected flywheel based electrical storage units 50 is determined. It is apparent from EQ. 3 that for flywheel based electrical storage units 50 1 to M, the current I that will be drawn therefrom will be equal to Imax for the respective flywheel based electrical storage unit 50, and the current I that will be drawn from flywheel based electrical storage unit M+1 may be less than the respective Imax.

(36) In order to avoid exceeding the predetermined maximum ΔP of stage 2000, in stage 2040 we determine for each flywheel based electrical storage unit 50 the expected change in current, denoted “4”. Some of flywheel based electrical storage units 50 which have up to now been supplying power, may now have their power draw disabled, whereas the M+1 selected flywheel based electrical storage units 50 will now receive enabling commands. The changes in current may be either positive or negative. Utilizing EQ. 2 we convert ΔP of stage 2000 into a maximum allowed ripple current, denoted “ΔImax”.

(37) In stage 2050, control circuit 30 sends a reduce current command to one of the flywheel based electrical storage units 50 of stage 2040 which has been determined to have a negative ΔI.sub.j so as to reduce its current by no more than ΔImax. In the event that ΔI.sub.j for the flywheel based electrical storage units 50 having a negative ΔI.sub.j is less than ΔImax, control circuit 30 sends the command to reduce it by ΔI.sub.j.

(38) In stage 2060, control circuit 30 sends an increase current command to one of the flywheel based electrical storage units 50 of stage 2040 which has been determined to have a positive ΔI.sub.j so as to increase its current by no more than ΔImax. In the event that ΔI.sub.j for the flywheel based electrical storage units 50 having a positive ΔI.sub.j is less than ΔImax, control circuit 30 sends the command to increase it by ΔI.sub.j.

(39) In stage 2070, the changes in stage 2050-2060 are compared with the determined changes of stage 2040. In the event that the changes of stage 2040 are not completed, control returns to stage 2050.

(40) In the event that they are complete, in stage 2080 the timer of stage 2000 is checked. In the event that the timer has not expired stage 2080 is repeated. In the event that the timer of stage 2000 has expired, control returns to stage 2000.

(41) While the term calculate is used herein, it does not necessarily require mathematical calculations in real time, and the use of a look up table with pre-calculated values is specifically included herein wherever the term calculate is used. Any method of determination, is thus meant to be included.

(42) FIG. 5 illustrates a high level flow chart of the operation of control circuit 30 to draw electrical energy from AC grid 15 to flywheel based electrical storage units 50, responsive to the difference between an allocated amount of power draw and the needs of PEV 80, i.e. in a situation where EVFCS 10, 100 is contracted to, or allowed to, take a predetermined amount of power while its PEV charging demand is less than that amount. As indicated above, the operation is being particularly described in relation to an EVFCS 10, 100, however this is not meant to be limiting in any way. EVFCS 10, 100 may be replaced by a station comprising one or more electrical storage units, coupled to an AC grid, with a local load, or a coupleable connection to a load, the electrical energy consumption of which load varies over time, without exceeding the scope.

(43) In stage 3000 control circuit 30 recognizes the imbalance and determines the available amount of power to store with an associated maximum amount of ripple, with the available amount of power denoted “Pavail” and the maximum amount of ripple denoted “ΔP”. ΔP may be predetermined for the system, or may be supplied periodically by DSO 20, without limitation. A timer is further set to ensure that the operation of FIG. 5 is repeated regularly during operation. In one embodiment, the timer of stage 3000 is set to 1 minute.

(44) In stage 3010, all of the flywheel based electrical storage units 50 are scanned to determine the presently available maximum power available from each of the N associated flywheel based electrical storage units 50, as described above in relation to EQ. 2.

(45) In stage 3020, the flywheels are sorted in ascending order of power. It is to be understood that stage 3020 is not strictly required, and is described herein for ease of understanding. In stage 3030, M+1 flywheel based electrical storage units 50 are selected in ascending order of power, such that:
Σ.sub.1.sup.M+1Pmax.sub.j≥Pavail>Σ.sub.1.sup.MPmax.sub.j  EQ. 4

(46) It is to be understood from EQ. 4 that M flywheels are being selected to operate at their respective Pmax, and flywheel M+1 may operate at less than Pmax. The current required being supplied to each of the M+1 selected flywheel based electrical storage units 50 is determined. It is apparent from EQ. 4 that for flywheel based electrical storage units 50 1 to M, the current I that will be input thereto will be equal to Imax for the respective flywheel based electrical storage unit 50, and the current I that will be input to flywheel based electrical storage unit M+1 will be less than the respective Imax.

(47) In order to avoid exceeding the predetermined maximum ΔP of stage 3000, in stage 3040 we determine for each flywheel based electrical storage unit 50 the expected change in current, denoted “ΔI.sub.j”. The changes in current may be either positive or negative. Utilizing EQ. 2 we convert ΔP of stage 2000 into a maximum allowed ripple current, denoted “ΔImax”.

(48) In stage 3050, control circuit 30 sends an increase current command to one of the flywheel based electrical storage units 50 of stage 3040 which has been determined to have a positive ΔI.sub.j so as to increase its current by no more than ΔImax. In the event that ΔI.sub.j for the flywheel based electrical storage units 50 having a positive ΔI.sub.j is less than ΔImax, control circuit 30 sends the command to increase it by ΔI.sub.j.

(49) In stage 3060, control circuit 30 sends a decrease current command to one of the flywheel based electrical storage units 50 of stage 3040 which has been determined to have a negative ΔI.sub.j so as to decrease its current by no more than ΔImax. In the event that ΔI.sub.j for the flywheel based electrical storage units 50 having a negative ΔI.sub.j is less than ΔImax, control circuit 30 sends the command to decrease it by ΔI.sub.j.

(50) In stage 3070, the changes in stage 3050-3060 are compared with the determined changes of stage 3040. In the event that the changes of stage 3040 are not completed, control returns to stage 3050.

(51) In the event that they are complete, in stage 3080 the timer of stage 3000 is checked. In the event that the timer has not expired stage 3080 is repeated. In the event that the timer of stage 3000 has expired, control returns to stage 3000.

(52) FIG. 6 illustrates a high level flow chart of the operation of a control circuit of any of the embodiments of FIGS. 1A-1C to maintain the electrical energy drawn from the AC grid within a predetermined range. In stage 4000, control circuit 30 receives a maximum power draw value, denoted PDMAX, optionally with a hysteretic threshold values. In one embodiment, as shown at stage 4090, the hysteretic threshold values are defined as evenly defined as higher, and lower than, than PDMAX, respectively, by an amount ΔPDMAX. In such an embodiment PDMAX represents the maximum power that may be drawn by the station, such as EVFCS 10, 100, from AC grid 15 within a threshold window—i.e. PDMAX is a target value, for which a range of +/−ΔPDMAX may be tolerated. This has been explained with a single hysteretic threshold ΔPDMAX, however this is not meant to be limiting in any way. Different threshold values may be provided for the threshold above PDMAX and the threshold below PDMAX, without exceeding the scope. The values PDMAX, higher and lower thresholds, and/or ΔPDMAX may be fixed at initial installation, or may be changed over time subject to information received from DSO 20. As indicated above, the use of hysteretic threshold is optional.

(53) In stage 4010, control circuit 30 determines the power drawn from AC grid 15 as PDRAW. In the embodiment of EVFCS 10 PDRAW may be input from power sensor 35 and in the embodiment of EVFCS 100 PDRAW may be input from the power sensor 35 associated with AC grid 15.

(54) In stage 4020 PDRAW is compared with a value THRESHOLD1, which in one embodiment is set to be equal to PDMAX−ΔPDMAX. In the event that PDRAW is less than THRESHOLD1, in stage 4030 electrical storage units 50 associated with control circuit 30 are polled to determine if each of electrical storage units 50 are fully charged. In the event that at least one electrical storage unit 50 is not fully charged, in stage 4040 control circuit 30 enables the at least one not fully charged electrical storage unit to draw electrical energy from AC grid 15, thus increases the electrical energy stored thereon. Control circuit 30 ensures that electrical storage units 50 are charged at a rate so as to ensure that PDRAW, which now includes power draw for charging at least one electrical storage unit 50, does not exceed PDMAX. In the event that in stage 4030, all of the electrical storage units 50 are fully charged, EVFCS 10, 100 is unable to increase its power draw, and stage 4000 is repeated. THRESHOLD1 thus represents a lower threshold value, and when the PDRAW is less than THRESHOLD1 additional electrical energy can be drawn from AC grid 15 to charge at least one electrical storage unit 50.

(55) In the event that in stage 4020, PDRAW is not less than THRESHOLD1, in stage 4050 PDRAW is compared with THRESHOLD2, which in one embodiment is equal to PDMAX+ΔPDMAX. If PDRAW is not greater than THRESHOLD2, then PDRAW is within the hysteretic window presented by THRESHOLD1 and THRESHOLD2 and stage 4000 is repeated. In such an embodiment, the maximum amount that may be drawn is allowed to temporarily exceed PDMAX provided that the amount drawn does not exceed THRESHOLD2, it being understood that PDMAX is a setting value, and not necessarily a physical absolute maximum. As will be understood by those skilled in the art, THRESHOLD2>THRESHOLD1. THRESHOLD2 thus represents a higher threshold value, and when the PDRAW is greater than THRESHOLD2 electrical energy drawn from AC grid 15 should be reduced, preferably by drawing electrical energy from at least one electrical storage unit 50.

(56) In the event that in stage 4050, PDRAW is greater than THRESHOLD2, i.e. an overdraw condition is experienced, in stage 4060 electrical storage units 50 associated with control circuit 30 are polled to determine if at least one electrical storage units 50 is capable of suppling electrical energy. In the event that in stage 4060 at least one electrical storage units 50 is capable of suppling electrical energy, in stage 4070 electrical energy is provided for a load of EVFCS 10, 100 from the at least one electrical storage units 50 capable of suppling electrical energy, while monitoring PDRAW so as to ensure that PDRAW is less than, or equal to, THRESHOLD2. Such a load may be presented by DC/DC charging unit 70 or AC/DC charging unit 130 having a connected vehicle. Advantageously, no communication with DC/DC charging unit 70 or AC/DC charging unit 130 is required.

(57) In the event that in stage 4060 none of electrical storage units 50 is capable of suppling electrical energy, in stage 4080 control circuit 30 outputs a flag to indicate a need to reduce PDRAW. Such a flag may signal an operator to disconnect at least one PEV 80. Alternately, in the event that a simple 1 bit communication is provided between control circuit 30 and DC/DC charging unit 70 or AC/DC charging unit 130, control circuit 30 may disable one or more DC/DC charging unit 70 or AC/DC charging unit 130, respectively, until PDRAW is reduced to below, or equal to, THRESHOLD2. Control circuit 30 may then continue to monitor PDRAW, and in the event that disabling a single DC/DC charging unit 70 or AC/DC charging unit 130, respectively, has not reduced PDRAW to below, or equal to, THRESHOLD2, additional DC/DC charging unit 70 or AC/DC charging unit 130 may be disabled. Power is re-enabled only after PDRAW is reduced to below THRESHOLD1.

(58) Alternately, in the event that more detailed control of DC/DC charging unit 70 or AC/DC charging unit 130 is available, power draw may be reduced by commanding the respected DC/DC charging unit 70 or AC/DC charging unit 130 to reduce its draw by a predetermined amount, or to maintain its draw below a predetermined value.

(59) FIG. 7A illustrates a high level block diagram of an embodiment of an electric vehicle fast charging station 200, where a first electrical vehicle is arranged to charge a second electrical vehicle. Electric vehicle fast charging station 200 is arranged as described above in relation to electric vehicle fast charging station 10, with the exception that DC/DC charging units 70 are replaced with bi-directional converters 210. FIG. 7B illustrates a high level flow chart of a method of operation of the arrangement of FIG. 7A to provide plug-in vehicle to plug-in vehicle charging, the figures being described together. FIGS. 7A-7B are particularly described in relation to electrical vehicles, however this is meant as an illustrating embodiment, and is not meant to be limiting in any way.

(60) Electric vehicle fast charging station 200 may operate as described above in relation to electric vehicle fast charging station 100, and in addition may provide electrical energy drawn from a first PEV 80 to a second PEV 80. First PEV 80 is configured with the ability to provide electrical energy via its charging port to a first port of the respective bi-directional DC/DC converters 210 to which it is connected. Such arrangements are well known to those skilled in the art of Vehicle to Grid technology, and in the interest of brevity will not be further described.

(61) Responsive to respective signals from control circuit 30, and as illustrated in stage 5000, the bi-directional converter 210 coupled to first PEV 80 is arranged to draw electrical energy from first PEV 80 through a first port of the respective bi-directional converter 210 and provide the drawn electrical energy to DC bus 60 through a second port of the respective bi-directional converter 210, as shown by the respective arrow. Further responsive to respective signals from control circuit 30, and as illustrated in stage 5010 the bi-directional converter 210 coupled to second PEV 80 is arranged to draw electrical energy from DC bus 60 through a second port of the respective bi-directional converter 210 and provide the drawn electrical energy to second PEV 80 through a first port of the respective bi-directional converter 210, thus charging second PEV 80 from the on-board storage of first PEV 80 as shown by the respective arrow.

(62) In one embodiment, as illustrated in optional stage 5020, the amount of electrical energy provided to DC bus 60 from first PEV 80 is substantially identical to the amount of electrical energy drawn from DC bus 60 to be provided to second PEV 80, and thus there is no electrical energy drawn from AC grid 15 or from electrical storage units 50 while still charging second PEV 80. Since each of bi-directional DC/DC converters 210 experience a certain amount of loss, any determination of amounts of electrical energy are preferably determined at the respective second port thereof, as determined by the respective current sensor 55.

(63) In another embodiment, as illustrated in optional stage 5030, the amount of electrical energy provided to DC bus 60 from first PEV 80 is less than the amount of electrical energy drawn from DC bus 60 to be provided to second PEV 80, and thus the difference in energy required to charge second PEV 80 is drawn from AC grid 15 and/or from electrical storage units 50.

(64) In another embodiment, as illustrated in optional stage 5040, the amount of electrical energy provided to DC bus 60 from first PEV 80 is greater than the amount of electrical energy drawn from DC bus 60 to be provided to second PEV 80, and thus the difference in energy is stored on electrical storage units 50, and/or provided to AC grid 15.

(65) The above has been described in relation to a modification of electric vehicle fast charging station 10, wherein each of the bidirectional converters 210 are DC/DC converters, as illustrated in optional stage 5050, however this is not meant to be limiting in any way. Similarly, electric vehicle fast charging station 100 may be modified by replacing AC/DC charging units 130 with bi-directional AC/DC converters, as illustrated in optional stage 5060.

(66) It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. In the claims of this application and in the description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

(67) Unless otherwise defined, all technical and scientific terms used herein have the same meanings as are commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods are described herein.

(68) All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the patent specification, including definitions, will prevail. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. No admission is made that any reference constitutes prior art. The discussion of the reference states what their author's assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art complications are referred to herein, this reference does not constitute an admission that any of these documents forms part of the common general knowledge in the art in any country.

(69) It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined by the appended claims and includes both combinations and sub-combinations of the various features described hereinabove as well as variations and modifications thereof, which would occur to persons skilled in the art upon reading the foregoing description.