Energy storage power supply using self-excitation of wound rotor induction motor

Abstract

The stored energy power supply uses a wound rotor induction motor (WRIM) to receive energy from a prime mover through a rotating shaft, provide magnetizing reactive energy from a self-excited AC capacitor bank, store energy in N energy storage elements (ESEs) through a tertiary winding, discharge the ESEs, and provide energy through a secondary winding to a load generating output. Each discharging ESE contributes to the total magnetic flux at the secondary winding to sum the voltages of the individual ESEs. These voltages can be stepped up or down depending on the transformation ratio between the secondary winding and each tertiary winding. The WRIM provides a safe, reliable, and efficient system for providing high level AC and DC output voltages.

Description

[Technical Field]

[0001] (Reference to Related Art) This application claims the benefit of priority to U.S. Patent Application No. 17 / 567,611, filed January 3, 2022, which is incorporated by reference herein in its entirety. [Background technology]

[0002] The present invention relates to receiving and storing power from an external source, and in particular to supplying energy to a load, using a wound rotor induction motor (WRIM) to receive energy from an external source such as a prime mover, magnetize the machine by self-excitation, store the energy in N energy storage elements (ESEs), and discharge the ESEs to supply the energy to a load-generating output. A flywheel may be used to buffer energy from the external source to the ESEs and the load-generating output. The WRIM provides a safe, reliable, and efficient system for supplying high-level AC and DC output voltages.

[0003] Description of Related Art Energy storage power supplies receive energy from an external source, AC or DC, store it, and deliver it to a load when needed. These types of energy storage power supplies store energy in several individual storage cells, such as batteries, high-density capacitors, or fuel cells. With current technology, each of these cells is limited to producing about 2 to 3 volts DC. To deliver a high DC output voltage, such as 1,000 volts, to a load, 500 storage cells may need to be connected in series across the load. Practical drawbacks include size, weight, reliability, loss of efficiency as individual cells age, and safety considerations.

[0004] As shown in Figure 1, energy storage power supply 10 includes an AC power source 12, such as might be provided by a utility grid, that supplies an AC input voltage via an AC mains bus 14. To assist in charging N batteries 16, a similar plurality of step-down transformers 18 and AC / DC rectifiers 20 step down the AC input voltage and convert it to a usable voltage, e.g., 2-3 V DC, to charge each of the N batteries 16. The batteries 16 are interconnected via contactors or electronic switches 22, which, when closed, provide a series connection of all of the batteries 16 to sum their individual voltages and provide a higher DC output voltage 24 across a load 26.

[0005] A voltage equalization network (VEN) 28 is connected across each of the batteries 16. Each VEN 28 includes a first switch Q1 in series with a resistor R1 to help balance battery terminal voltage differences among the group of N batteries. Each VEN 28 also includes a second switch Q2 in parallel with Q2 / R1 to act as a bypass in the event of a failure of a particular battery 16.

[0006] Due to size, weight, reliability, efficiency loss, and safety considerations, this approach is not practical when the number of batteries is larger, for example, sufficient to provide a DC output voltage of 1,000 V. Summary of the Invention

[0007] The following is a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description and claim definitions that are presented later.

[0008] The present invention provides a stored energy power supply that uses a wound rotor induction motor (WRIM) to receive energy from an external power source, stores the energy in N energy storage elements (ESEs), and discharges the ESEs to provide energy to a load-generating output. The WRIM provides a safe, reliable, and efficient system for providing high level AC and DC output voltages.

[0009] In one embodiment, the WRIM includes N tertiary windings, each wound at 360 / N degrees and distributed around a first magnetic core, and a secondary (e.g., rotor) winding wound at 360 degrees around a second magnetic core coupled to a load-generating output. The first and second magnetic cores are separated by a radial air gap and configured to rotate relative to one another. N bidirectional AC / DC converters couple each of the tertiary windings to a respective energy storage element (ESE). Each ESE includes one or more series-connected accumulators, such as batteries, high-density capacitors, or fuel cells. In a charging state, the WRIM controller couples an external energy source to the WRIM to create a rotating magnetic field, resulting in relative rotation between the first and second magnetic cores (e.g., a stationary stator winding and a rotating rotor winding), magnetizing the tertiary winding and supplying power through the AC / DC converter to selectively charge the N ESEs. In a discharge state, the WRIM controller reverse-discharges the capacitances of at least some of the N ESEs through the AC / DC converter, exciting the tertiary windings to form a rotating magnetic field that magnetizes the air gaps and individually contributes to the overall magnetic flux, magnetizing the secondary windings and inducing an AC output voltage in the secondary windings that is proportional to the sum of the voltages from the discharged energy storage elements, thereby supplying energy to the load-generating output. The AC output voltage may be rectified to provide a DC output voltage.

[0010] In one embodiment, the external energy source is a prime mover (such as an engine, wind turbine, or gas turbine) coupled to the WRIM, rotating its shaft to cause relative rotation of the first and second magnetic cores and magnetize the radial air gaps with reactive excitation provided by one or more AC capacitor banks. The one or more capacitor banks are coupled to the primary winding (if used) or one or more tertiary windings of the first magnetic core to provide lagging power factor reactive power required to magnetize the radial air gaps and leading power factor reactive power to balance leakage inductances in any of the windings, to excite the tertiary windings, and to provide controlled power via an AC / DC converter to selectively charge the N ESEs. It is understood that other types of external energy sources and methods of coupling energy into the WRIM are contemplated and within the scope of the present invention.

[0011] In one embodiment, the WRIM includes a primary winding wound 360 degrees around the first magnetic core and coupled to an AC capacitor bank that provides lagging power factor reactive power for self-excitation. In another embodiment, the primary winding is omitted or not connected. One or more AC capacitor banks are coupled to respective tertiary windings to provide reactive power for self-excitation. The ESEs coupled to the respective AC capacitor banks via the tertiary windings can be charged and discharged independently.

[0012] In an embodiment, the AC output voltage is scaled by a transformation ratio defined by the number of turns on the secondary winding relative to the number of turns on each of the tertiary windings. A step-up transformer's transformation ratio is greater than 1:1 and functions to increase the output voltage. For example, assume a 5:1 turns ratio and four ESEs, each supplying 50V DC. Discharging all four ESEs simultaneously can provide an AC output voltage of 1,000V AC (calculated as 50*4*5). The step-up transformer's transformation ratio can support much higher output voltages with far fewer batteries. Alternatively, the turns ratio can be designed to provide a step-down transformer's transformation ratio (less than 1:1) to accommodate low-voltage loads.

[0013] In an embodiment, the WRIM optionally includes a flywheel coupled to the shaft. Each of the ESE, flywheel, power conditioning converter, and load is appropriately configured for bidirectional energy transfer. Energy may flow from the prime mover to charge the ESE or flywheel, or directly to the load. Energy from the ESE may flow to the load or possibly the flywheel. Energy from the flywheel may flow back to charge the ESE or to the load. Finally, energy stored in the load, if unused, may be transferred back to the ESE and flywheel.

[0014] In an embodiment, the primary (e.g., stator) winding (if used), the secondary (e.g., rotor) winding, and each of the N tertiary windings are electrically isolated from one another, and the N ESEs are electrically isolated from one another.

[0015] In an embodiment, assuming a single primary (e.g., stator) winding is coupled to an AC capacitor bank and N tertiary windings share the same stator slot of the WRIM, the N bidirectional AC / DC converters are independently controllable to either exclusively selectively charge one or more ESEs, or (XOR) independently controllable to selectively discharge one or more ESEs. A single primary cannot simultaneously charge and discharge different ESEs.

[0016] In an embodiment, a primary (e.g., stator) winding is segmented into M primary windings, each of which is coupled to an AC capacitor bank. Each AC capacitor bank is preferably a multi-phase capacitor bank. Each primary winding is magnetically coupled to one or more tertiary windings. The WRIM controller is configurable to independently charge or discharge ESEs that are oppositely coupled to different primary windings and AC capacitor banks. The WRIM controller can simultaneously charge one or more ESEs coupled to a first subset of the M primary windings and discharge one or more ESEs coupled to a second subset of the M primary windings, where the first and second subsets do not overlap. For example, if six primary windings are each coupled to two tertiary windings (12 total tertiary windings), the WRIM controller can simultaneously charge the ESEs coupled to the six first tertiary windings while discharging the ESEs coupled to the six second tertiary windings.

[0017] In an embodiment, when the ESEs discharge, their terminal voltages decrease, which can cause the AC output voltage to fall below the target voltage. Alternatively, the AC output voltage may exceed the target voltage for other reasons. A load power factor controller can be coupled to the load-generating output to modulate the inductive resistive load and actively adjust the power factor of the WRIM to vary the shaft rotational speed and maintain the AC output voltage within a specified tolerance of the target voltage. For example, an increase in slip (a decrease in rotor speed) increases the induced AC output voltage to account for the decrease in ESE voltage.

[0018] In an embodiment, a flywheel is coupled to the shaft to store kinetic energy when the flywheel accelerates and return kinetic energy to the WRIM when the flywheel decelerates. The flywheel may be directly coupled to the WRIM shaft or may have an intermediate gearbox that provides speed change between the WRIM and the flywheel. In an embodiment, the WRIM controller charges both the ESE and the flywheel to store energy. In the case of a battery, for example, the ESE charges slowly, with a much longer time constant than the flywheel. In an embodiment, the WRIM controller discharges both the ESE and the flywheel to provide energy to the load. The ESE provides energy quickly, with a much shorter time constant than the flywheel. Typically, the flywheel begins providing energy once the ESE is partially depleted. The flywheel can be used to "buffer" the energy / power provided by the prime mover through the WRIM to the load-generating output. As a result, the peak power capability of the prime mover may be much lower than the peak power it can provide to the load. The input power from the prime mover is integrated over time and then released, for example, in a large transient pulse.

[0019] In different embodiments, the WRIM controller decouples the prime mover from the WRIM to supply energy to the load using only the energy stored in the ESE and the flywheel (if provided), or leaves the prime mover coupled to the WRIM to supply additional energy to the load.

[0020] These and other features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0021] [Figure 1]As mentioned above, a block diagram of a known energy storage power supply is shown, in which a step-down transformer is configured to charge individual batteries, which are connected in series, sum their voltages, and supply energy to a load. [Figure 2] FIG. 1 is a block diagram of an energy storage power system that uses a prime mover to provide energy to a WRIM, which transfers energy to and from individual ESEs to provide energy to loads. [Figure 3] FIG. 1 illustrates bidirectional energy flow between the prime mover, ESE, flywheel, and load. [Figure 4A] Schematic diagram of a three-phase energy storage power system in which an AC capacitor bank is coupled to the primary (stator) winding to provide the leading power factor reactive power required for self-excitation of the WRIM, bidirectional AC / DC converter, and load power factor controller used therein. [Figure 4B] Schematic diagram of a three-phase energy storage power system in which an AC capacitor bank is coupled to the primary (stator) winding to provide the leading power factor reactive power required for self-excitation of the WRIM, bidirectional AC / DC converter, and load power factor controller used therein. [Figure 4C] Schematic diagram of a three-phase energy storage power system in which an AC capacitor bank is coupled to the primary (stator) winding to provide the leading power factor reactive power required for self-excitation of the WRIM, bidirectional AC / DC converter, and load power factor controller used therein. [Figure 5A] FIG. 1 is a diagram of a 12-pole WRIM embodiment in which the primary (stator) winding is wound 360 degrees around the fixed magnetic core, the secondary (rotor) winding is wound 360 degrees around the rotating magnetic core, and three tertiary windings are each wound at 120 degrees around the fixed magnetic core to provide three isolated energy ports, and also shows the winding of the tertiary windings. [Figure 5B]FIG. 1 is a diagram of a 12-pole WRIM embodiment in which the primary (stator) winding is wound 360 degrees around the fixed magnetic core, the secondary (rotor) winding is wound 360 degrees around the rotating magnetic core, and three tertiary windings are each wound at 120 degrees around the fixed magnetic core to provide three isolated energy ports, and also shows the winding of the tertiary windings. [Figure 6] FIG. 1 is a diagram of an embodiment of a WRIM in which the primary (stator) winding is segmented into six segments, each magnetically coupled to an AC capacitor bank and two tertiary windings to facilitate simultaneous charging and discharging of ESEs assisted by different segments of the primary winding. [Figure 7A] FIG. 10 is a winding diagram of the primary, secondary, and six tertiary windings of a 12-pole WRIM embodiment with six isolated energy storage ports. [Figure 7B] FIG. 10 is a winding diagram of the primary, secondary, and six tertiary windings of a 12-pole WRIM embodiment with six isolated energy storage ports. [Figure 7C] FIG. 10 is a winding diagram of the primary, secondary, and six tertiary windings of a 12-pole WRIM embodiment with six isolated energy storage ports. [Figure 7D] FIG. 10 is a winding diagram of the primary, secondary, and six tertiary windings of a 12-pole WRIM embodiment with six isolated energy storage ports. [Figure 8A] 7A to 7D. FIG. [Figure 8B] 7A to 7D. FIG. [Figure 8C] 7A to 7D. FIG. [Figure 9] FIG. 10 is a diagram of an alternative embodiment of a WRIM in which one or more AC capacitor banks are coupled to each tertiary winding to provide leading power factor reactive power required for self-excitation. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention provides a stored energy power supply that uses a wound rotor induction motor (WRIM) to receive energy from an external source, such as a prime mover, stores energy in N energy storage elements (ESEs) through self-excitation of the WRIM, and supplies energy to a load-generating output by discharging the ESEs. Energy storage and supply can be supplemented with a rotor-mounted flywheel. The WRIM provides a safe, reliable, and efficient system for providing high-level AC and DC output voltages.

[0023] As used herein, a prime mover is any machine that converts one or more forms of energy (chemical, electrical, fluid pressure / flow, etc.) into mechanical force to rotate a shaft coupled to a magnetic core and possibly a flywheel. Examples of prime movers are combustion engines, wind turbines, or gas turbines.

[0024] As used herein, generally speaking, a WRIM may or may not, depending on the embodiment, include a primary winding wound 360 degrees around a first magnetic core, a secondary winding wound 360 degrees around a second magnetic core configured to rotate relative to the first magnetic core and coupled to a load-generating output, and N tertiary windings, each wound 360 / N degrees, distributed around the first magnetic core, and magnetically coupled to both the primary winding (if used) and the secondary winding. Generally, the primary (stator) winding and tertiary winding may be wound on either magnetic core, and the secondary (rotor) winding may be wound on the other core that rotates relative to each other. More conventionally, the primary (stator) winding is wound on a fixed magnetic core, and the rotor winding is wound on an inner magnetic core that rotates inside the fixed magnetic core. Without loss of generality, embodiments of the present invention will be described using conventional nomenclature for stator and rotor windings, with an additional tertiary winding distributed around the fixed magnetic core. Furthermore, the windings may be single-phase or multi-phase. Without loss of generality, the present invention will be described using a conventional three-phase winding.

[0025] Referring now to FIG. 2 , an embodiment of an energy storage power supply 200 includes a WRIM 202. The WRIM 202 has a stator winding S 204 wound 360 degrees around a fixed magnetic core 206, a rotor winding R 208 wound 360 degrees around a rotating magnetic core (“rotor”) 210 configured to rotate inside the fixed magnetic core 206, and N tertiary windings T1, T2, ..., TN212, each wound 360 / N degrees, distributed around the fixed magnetic core 206, and magnetically coupled to both the primary and secondary windings. A radial air gap 213 separates the rotor 210 from the fixed magnetic core 206. The stator winding 204 is shown as a single, general multi-phase uniformly distributed winding. As described below, the stator winding may be segmented into M segments, each magnetically coupled to one or more tertiary windings. The stator, rotor, and tertiary windings have respective turns ratios Ns, Nr, and Nt(i), for i = 1 to N. The stator-to-tertiary ratio Ns / Nt(i) determines the magnitude of the AC voltage at each of the tertiary windings. The rotor-to-tertiary ratio Nr / Nt(i) determines the transformation ratio (step-up or step-down) from the tertiary winding to the rotor winding. An energy storage port 214 is coupled to each tertiary winding 212, and a load-generating output 216 is coupled to the rotor.

[0026] Prime mover 218 rotates shaft 220 which rotates rotor 210, powering WRIM 202. AC capacitor bank 204 is coupled to stator winding S 204. AC capacitor bank 221 provides leading power factor reactive power to balance the leakage inductance of the windings and the lagging power factor reactive power required to magnetize the radial air gap, allowing the WRIM to be "self-excited."

[0027] Each port is connected to a bidirectional AC / DC converter 224, which is connected to an energy storage element (ESE) 226. The ESEs are preferably electrically isolated 228 from one another. Each ESE 226 includes one or more series-connected storage cells 230, such as batteries, high-density capacitors, or fuel cells. With current technology, each cell can generate approximately 2-3 V DC when fully charged. The ESEs may or may not be identical and may or may not generate the same total DC voltage. Consequently, the primary-to-tertiary winding ratio can be designed to provide different DC voltages for charging different ESEs.

[0028] To start the WRIM and bring the rotor 210 up to speed, a prime mover 218 is used to provide starting energy to bring the shaft 220 and flywheel 240 up to a nominal speed and store energy. A gearbox 241 may or may not be used. In a preferred embodiment, the gearbox increases the speed of the prime mover, allowing the flywheel 240 and WRIM 202 to run faster than would otherwise be possible, and therefore, a higher power density. The ESE AC / DC converter 224 is de-energized, opening the tertiary winding 212. Once the rotor 210 has risen to a nominal shaft speed (e.g., 3600 rpm), the rotor places a capacitor shunt excitation in place via winding 204, magnetizing the tertiary winding 212.

[0029] To selectively charge one or more of the ESEs 116, a prime mover 218 rotates a shaft 220 to magnetize the radial air gap 213 with reactive excitation provided by an AC capacitor bank 221 coupled to the stator winding S204, self-exciting the WRIM. The AC capacitor bank provides lagging power factor reactive power required to magnetize the radial air gap 213 and leading power factor reactive power to balance the winding leakage inductance, exciting the tertiary winding 212 and providing controlled power via an AC / DC converter 224 to selectively charge the N ESEs 226. If a particular AC / DC converter 224 is powered off, that ESE 226 is not charged.

[0030] When discharged, each ESE generates an AC voltage through its respective converter 224 that excites its corresponding tertiary winding 212 at its energy storage port 214, creating a rotating magnetic field that magnetizes the radial air gap 213 between the rotor and the stationary magnetic core, delivering net power to the rotor magnetic core and individually contributing to the total magnetic flux magnetically coupled to the rotor winding 208. The AC voltage at the energy storage port, and therefore its contribution to the total magnetic flux, is scaled by a transformation ratio, Nr / Nt(i). When the ratio is greater than 1, it functions as a step-up transformer to increase the tertiary voltage level. When the ratio is less than 1, it functions as a step-down transformer to decrease the tertiary voltage level. As each ESE is selectively energized through its converter, the machine's magnetic flux increases in controllable steps up to the magnetic saturation limit. One or more ESEs can be selectively charged or discharged simultaneously or sequentially.

[0031] The rotating magnetic field and corresponding total magnetic flux induces an AC output voltage VoutAC in the rotor winding 208 proportional to the sum of the voltages from the discharging ESEs 226 weighted by their respective rotor-to-tertiary winding ratios, delivering the coupled energy to the load-generating output 216. If necessary, a bidirectional AC / DC converter 232 converts the AC output voltage of the tertiary winding to a DC output voltage VoutDC. The output voltage VoutAC or VoutDC is used to charge a pulse-forming network (PFN) 234 or is delivered directly to a load 236 without a PFN. The PFN 234 is comprised of inductive and capacitive elements arranged to sharpen the pulse of energy, as described further below. The PFN 234 can at least temporarily store the energy provided by the WRIM before it is released to the load 236.

[0032] As an example, with the WRIM rotating at or near full speed, each of the ESEs 226 is charged to its full-rate voltage. This is a low voltage, such as 48 volts DC, representing 24 battery cells in series at 2.0 volts each. Energy for charging is extracted from the prime mover 218. The purpose of the energy storage power supply 200 is to generate a high voltage, such as 1,000 V DC, at the final output, which corresponds to a minimum of three-phase 750 volts AC at the mechanical windings. In charging mode, the input voltage of the stator windings is moderately high, and the tertiary winding is wound with fewer turns, allowing cell charging at a low voltage, such as 48 V DC, for a bank of cells, requiring an AC voltage for each ESE's AC / DC converter 224 of approximately 38 volts line-to-line, three phases. If a WRIM is wound for 480 volts AC on the stator, an exemplary voltage turns ratio is 480:38, or 12.6:1. For actual mechanical windings requiring integers, the winding turns ratio should be 12:1. As an example, if three ESEs are configured, each with a corresponding AC / DC converter capable of achieving a nominal terminal voltage of 38 VAC, and a final AC output of 750V is required, the rotor-to-tertiary voltage ratio would be 750:(3 x 38) or 6.58:1 (ignoring mechanical slip). In practice, the WRIM would have the next highest integer for the winding turns ratio, resulting in a rotor-to-tertiary turns ratio of 7:1. It is important to note that a 1,000V DC output can be produced with only 72 battery cells, whereas a series-connected power supply would require 375 battery cells.

[0033] A flywheel 240 may optionally be mechanically coupled to the rotor 210 via the shaft 220 to both store and supply kinetic energy. As is known, energy is stored in the flywheel by increasing rotor speed and released from the flywheel by decreasing rotor speed. An intermediate gearbox 241 may be used to effect speed changes between the WRIM and the flywheel. The rotor speed is primarily controlled by the prime mover 218. The flywheel 240 is typically charged by the prime mover, but may also be charged by excess energy from either the load or the ESEs. The flywheel 240 delivers energy with a time constant longer than the discharge time constant of the ESEs 226. For example, in an embodiment, one or more of the ESEs 226 are discharged to provide a burst of energy to the load. When the ESEs 226 are partially discharged, the flywheel 240 is used to supply energy to the load through the rotor 210 with a much longer time constant. This coupled discharge characteristic is often beneficial to the load.

[0034] In an embodiment, the WRIM controller charges both the ESE and the flywheel to store energy. In the case of a battery, for example, the ESE charges slowly and has a much longer time constant than the flywheel. In an embodiment, the WRIM controller discharges both the ESE and the flywheel to provide energy to the load. Current technology allows the ESE to provide energy quickly, with a much shorter time constant than the flywheel. Typically, once the ESE is partially depleted, the flywheel begins to provide energy. The flywheel can be used to "buffer" the energy / power provided by the prime mover through the WRIM to the load-generating output. As a result, the peak power capability of the prime mover can be much lower than the peak power it can provide to the load. The input power from the prime mover integrates over time and then is released, for example, in large transient pulses.

[0035] The WRIM controller 242 generates control signals to open / close (off / on) the ESE AC / DC converter 224, the output AC / DC converter 232, and to the prime mover 218 to rotate the shaft 218 and charge or discharge the flywheel 240. As will be explained in connection with Figure 3, in a fully bidirectional system there are many different "modes" for supplying, storing, and delivering energy.

[0036] In a WRIM, the stator and tertiary windings always have the same frequency, f1, regardless of rotor speed. The rotor output winding frequency, f3, is a variable that depends on the shaft speed, omegaR. The frequency of the rotor circuit is f3 = s * f1, where f1 is the primary winding frequency (Hz) of either winding 204 or winding 212, s is the slip per unit defined as s = (omegaS - omegaR) / omegaS, where omegaS is the synchronous shaft speed defined as 2 * Pi * f1 / pole pair, and omegaR is the actual shaft speed, both in radians / second.

[0037] When the WRIM200 is running near its synchronous (full) speed, the rotor f3 output frequency will be low. For example, if slip = 0.10 per unit and f1 is 400 Hz, the rotor frequency will be 40 Hz. This is acceptable because the purpose of the output is to rectify this rotor frequency and produce a high voltage DC output, and the actual frequency is not very important. Conversely, if the WRIM shaft speed is at the half-speed point and slip = 0.50 per unit, a higher output frequency of 200 Hz is also rectified to DC and acceptable.

[0038] Consider the case where the ESE is fully charged and ready to discharge. The prime mover is disconnected. Once converted to AC, the tertiary winding power from the ESE sum provides magnetic excitation to the radial flux in the WRIM air gap. At standstill, the induced rotor flux due to the combined action of the tertiary windings reaches a maximum value. At full synchronous speed, the induced rotor flux is close to zero. At a practical operating slip, such as 10%, the induced rotor flux is 10% of its standstill value.

[0039] In a WRIM, the entire power output of the combined ESE passes through the induction machine. This is defined as slip power, and there is always a nominal slip value, e.g., 10%. The efficiency of the machine as an energy converter is typically 92-95%, resulting in a rotor output power of 0.92-0.95 per unit of full power. However, the most important aspect is voltage step-up conversion. As previously shown, if the desired overall rotor-to-tertiary voltage conversion ratio is 7:1 and the operating slip is 10%, the actual winding turns ratio should be 10 x 7, or 70:1. The effective turns ratio is Nr / (Nt(i) * slip), which is a realistic number for implementation. For example, the tertiary windings can have 12 turns per phase, and the ESEs collectively have 36 turns per phase each, resulting in a rotor wound with 2520 turns per phase. In a 12-pole machine, this amounts to 210 turns per phase per pole. The rotor may typically have 3 slots / pole / phase, so the turns per slot per phase is 70 turns.

[0040] Another practical issue is that as the energy stored in each ESE is depleted by its discharge, its terminal voltage also decreases. It is desirable to maintain the load-generated output, VoutAC or VoutDC, within a specified tolerance of the target value. One known approach is to control the AC / DC converter 224 to vary the ratio of the input voltage to the output voltage. The converter is built with an active leading edge that can boost or maintain the AC output voltage constant by the gating action of a switching device when in inverting mode to compensate for the continuous decrease in DC input voltage from the discharging ESE. A new approach (shown in more detail in FIG. 4C) uses the load factor power controller 244 (known per se for performing capacitive load compensation to restore a power factor of one) to either (a) reduce the power factor of the secondary load circuit from a purely resistive load (unity power factor) or (b) make it a resistive load shunted by an auxiliary and controllable inductive branch. This effectively corrects the slip, which in turn corrects the conversion ratio to maintain Vout at the target value.

[0041] In an alternative embodiment, two rotor assemblies 408 and 410 are connected to a common shaft 420 and to a common prime mover 418. Each rotor operates within a separate stator assembly 404, with each stator having separate energy storage elements 426 of N1 and N2 ESEs and N1 and N2 tertiary windings 412 magnetically coupled to two or more independent electrical loads.

[0042] As shown in Figure 3, the depiction of energy storage power supply 200 is simplified to show the different bidirectional energy flows through the system and the different "modes" of operation. The rotor winding output AC / DC converter and load factor power controller are omitted for simplicity. Each of the windings is shown as three phases. Similar reference numbers to Figure 2 are maintained for clarity.

[0043] Regardless of the exact number of electrostatic (electrochemical) batteries / banks (ESE), it is understood that there can be four different types of energy storage technologies in an energy storage power source. 1. Flywheel inertial energy storage. 2. Electrostatic / electrochemical energy storage at low voltage levels. 3. Capacitive energy storage in the output pulse forming network (PFN) at high voltage levels. 4. Magnetic energy storage in electric machines (WRIM) air gaps and winding inductances. Energy is defined as: E1 = Prime Mover Energy. Ef = Flow of flywheel kinetic energy entering the WRIM rotor as mechanical energy and leaving the rotor. EFm = Maximum amount of kinetic energy stored in the flywheel at a specified maximum speed. ES1, ES2, ES3 = energy flow into and out of each ESE, required AC / DC converters have zero or minimal energy storage. Note that the amount of energy may vary between ESEs. Eo = intermediate output energy generated or absorbed by the WRIM rotor winding, in the preferred embodiment this is a high or medium voltage output, this energy after AC / DC rectification is used to charge the pulse forming network or power load directly without a PFN. Efo = Final energy output of the pulse forming network (PFN), the PFN stores energy in its capacitor bank and contains output electronic switches such as thyristors to control the flow of energy to the load resistors so that it can release a large amount of energy at once or split this energy into smaller amounts.

[0044] In the most common configuration, the flywheel, ESE, and load transfer energy in both directions. The WRIM controller can turn different energy sources on and off through the converter in virtually any combination to transfer and store energy from any source to any other.

[0045] The most important aspects of system energy flow are contained in seven fundamental modes.

[0046] Mode 0 - Energy from the E1 prime mover initially charges the flywheel, i.e., E1 = Ef + WRIM windage losses. After a period of time, E1 charges multiple ESEs from the prime mover via ES1, ES2, and ES3, where E1 = ES1 + ES2 + ES3, and small losses in the three AC / DC converters and tertiary winding losses are compensated by the stator winding S.

[0047] Mode 1 - A portion of the flywheel output inertial energy Ef is combined with the sum of storage energy ES1, ES2, and ES3, which are released into multiple sets of tertiary windings to provide the maximum possible output energy Eo (stored in the WRIM), which is then rectified to a load-generating output from the rotor winding R, and the resulting DC power is routed to a pulse forming network capacitor energy bank (PFN) and then to the final load.

[0048] Mode 2—The prime mover is powered off. The flywheel was precharged either in Mode 1 or from another mode from a previous engagement or mission. Flywheel energy is held at a maximum motion level, Efm, and is not initially released. Electrostatic (or electrochemical) sources ES1, ES2, and ES3 at low voltage levels are magnetically coupled by the rotor windings with optional commutation. These energies, ES1, ES2, and ES3, are released, producing output energy Eo and a final power output, Efo, bringing the ESE down to approximately half its potential energy level. The flywheel is then used to collectively recharge the ESE according to the balance equation, Ef = ES1 + ES2 + ES3, whereby the rotor winding R is used to magnetize the machine air gap and also functions as a voltage / power generating winding to recharge the ESE at a controlled rate. This mode assumes that the flywheel is rotating for the entire duration of this mode.

[0049] Mode 3—The prime mover is on, and the stator winding S is excited via an AC capacitor bank. The flywheel was precharged either in Mode 1 or from another mode from a previous engagement or mission. Flywheel energy is maintained at its maximum kinetic level, Efm, and is not initially released. Low-voltage ESEs ES1, ES2, and ES3 are magnetically coupled by the rotor winding. After commutation, they are discharged, producing output energy Eo and final power Efo, and the ESEs are reduced to approximately half their potential energy level. The rotating prime mover and flywheel then jointly recharge the electrostatic sources according to the balance equation (E1 + Ef) = ES1 + ES2 + ES3, thereby using the stator winding S to magnetize the machine air gap, and the rotor winding functions as a voltage / power generating winding to recharge the ESEs at a controlled rate based on the flywheel now providing a portion of its kinetic energy. Multiple AC / DC converters independently control the charge rate to each energy source to prevent overcharging.

[0050] Mode 4 - ESEs are sequentially discharged or only one ESE is fully discharged. ES1 is fully discharged and ES2 and ES3 are actively discharging but not yet depleted. By using an independent AC / DC converter to regulate the current, voltage, and power / energy to the ESEs, the flywheel energy Ef charges ES1 and also contributes to the primary output energy Eo, which can be expressed as: Ef=ES1+k1(Eo), where k1 is the proportionality constant of the flywheel contribution to the load, e.g., 0.30 per unit; ES2+ES3=k2(Eo), where k2 is the proportionality constant of the two energy sources contributing to the output load, e.g., 0.70 per unit, k1+k2=1.0 per unit.

[0051] Because the previous discharge functions of Mode 5-ES1 through ES3 have charged the PFN to its full capacitive energy storage level E-PFN, and the final load is not started or connected, the control system must return the PFN's output energy to the WRIM, which then distributes this recovered energy Eo to either the flywheel, the ESEs, or both. Again, the rotor winding functions to magnetize the machine's air gap and acts as a generator winding, supplying a portion of the output energy Eo (stored in the PFN) to one, two, or three of the ESEs, depending on their individual energy levels. The AC / DC converter control system determines which ESE has the lowest voltage / charge level and gives priority to this source in obtaining this recovered energy. If the ESE cannot accept any further portion of Eo and the flywheel is fully charged (i.e., Ef = Efm), this recovered energy Eo must be discharged to an external resistor bank.

[0052] Mode 6 - The majority of the ESE is fully charged. The prime mover is disconnected and the rotor is initially stationary. When there is a demand to charge the PFN to start the load, energy is transferred from the ESE to activate the WRIM and bring the rotor and flywheel up to a useful operating speed. Energy from the flywheel or ESE, or both, is then collectively used to energize the PFN and the load.

[0053] 4A-4C, an embodiment of a three-phase energy storage power supply 400 includes a WRIM 402. The WRIM 402 has a three-phase stator excitation winding S 404 wound 360 degrees around a fixed magnetic core 406, a three-phase rotor winding R 408 wound 360 degrees around a rotating magnetic core ("rotor") 410 configured to rotate inside the fixed magnetic core 406, and N three-phase tertiary windings T1, T2, ..., TN 412, each wound 360 / N degrees, distributed around the fixed magnetic core 406, and magnetically coupled to both the primary and secondary windings. The rotor windings typically include a set of three slip rings and an electric brush set to transfer AC current to and from the rotor.

[0054] The three-phase stator excitation windings are shown as "delta" windings, although other common configurations such as wye can be used. The stator, rotor, and tertiary windings have respective turns ratios Ns, Nr, and Nt(i), for i = 1 to N. The stator-to-tertiary ratio Ns / Nt(i) determines the magnitude of the AC voltage at each of the tertiary windings. The rotor-to-tertiary ratio Nr / Nt(i) determines the transformation ratio (step-up or step-down) from the tertiary winding to the rotor winding. A three-phase energy storage port 414 is coupled to each three-phase tertiary winding 412, and a three-phase load generation output 416 is coupled to the rotor.

[0055] Prime mover 418 rotates shaft 420 and, optionally, a flywheel 413 coupled to the shaft to power the WRIM. Prime mover 418 rotates shaft 420 to magnetize the radial air gap and self-excite the WRIM with reactive excitation provided by AC capacitor bank 415 (e.g., three capacitors connected in a delta configuration) coupled to three-phase stator winding S404 through vacuum circuit breaker 417. The AC capacitor bank provides lagging power factor reactive power required to magnetize the radial air gap and leading power factor reactive power to balance the leakage inductance of the primary and tertiary windings of the stationary magnetic core, exciting tertiary winding 412 and providing regulated power at three-phase energy storage port 414.

[0056] Each three-phase energy storage port 414 is connected to a bidirectional three-phase AC / DC converter 424, which is connected to an energy storage element (ESE) 426. When the AC / DC converter 424 is controlled to operate in a rectifying mode, a DC voltage and power is applied to the ESE 426, charging the ESE. When the AC / DC converter 424 is controlled to operate in a reversing mode, the ESE 426 discharges and generates an AC voltage at the tertiary winding, which contributes to the total magnetic flux magnetically coupled to the rotor winding 404, generating a three-phase output voltage VoutAC at the three-phase load generating output 416.

[0057] The output power is conducted through a three-phase bidirectional AC-DC converter 430 to a pulse forming network (PFN) 432. The PFN is shown as a two-stage PFN (L1, C1, L2, C2), whereby charging of the PFN is controlled by series-connected solid-state switches SWx, such as IGBTs or thyristors, connected to the input side of inductor L1. The output load RL434 is controlled by closing switch SW1, which can be solid-state or electromechanical.

[0058] A load power factor controller 438 is connected at the three-phase output of the rotor winding to the three-phase load generating output 416. After the WRIM reaches full speed, the controller 438 can add inductance to the otherwise resistive load 434 to reduce the power factor of the WRIM. This increases the rotor current and also modifies the operating slip, which changes the rotor rotational speed to maintain the AC output voltage within tolerance of the target voltage.

[0059] FIG. 4B shows an industry-standard bidirectional three-phase AC / DC converter 424 embodiment. The AC / DC converter 424 includes a three-phase passive diode bridge rectifier 450 and an active thyristor (or IGBT) inverter 452 connected in parallel between the tertiary winding 412 and the ESE 426 at the three-phase energy storage port 414 to alternately charge and discharge the ESE, respectively. The rectifier 450 includes three pairs of series-connected diodes 454. The three-phase energy storage port 414 is connected between each pair of diodes 454. The rectifier 450 converts the three-phase AC voltage at the energy storage port 414 into a DC voltage that is applied to charge the ESE. The inverter 452 includes three pairs of series-connected thyristors 456. A gating controller 458 controls the gates of the three thyristors 456. 3 The three-phase energy storage port 414 is connected between each pair of diodes 454. The inverter 452 converts the DC voltage of the ESE to a three-phase AC voltage at the energy storage port 414 to discharge the ESE and drive the load. See "A BASIC GUIDE TO POWER ELECTRONICS" BY Albert Kloss, John Wiley & Sons, Ch 8 Power Balance in Three-Phase Bridge Converters, pages 100-115, 1984.

[0060] FIG. 4C shows an industry-standard embodiment of a load factor power controller 438. The load power factor controller 438 is connected to the three-phase load generating output 416 at the rotor output. The controller has three legs, each of which includes a series connection of an inductor 460 (L1, L2, L3), preferably an air-core AC inductor, a resistor (R1, R2, R3), and a pair of thyristors 462 and 464 connected in anti-parallel to produce bidirectional current. A gating phase angle controller 466 receives input signals from the WRIM controller and generates control signals on the gate leads of each thyristor. The load factor power controller 438 changes the power factor of the load circuit from purely resistive to partially inductive, thereby reducing the power factor from near unity to a lagging value. This increases rotor current and corrects operating slip, which in turn changes the rotor rotational speed to maintain the AC output voltage within a target voltage tolerance. The use of a polyphase induction bank means that there is no appreciable actual power loss in this speed slip control scheme. See "Induction Machines" by Philip L. Alger, Gordon and Breach Science Publishers, CH 8, pages 261-265, 1970.

[0061] 5A and 5B, an embodiment of a WRIM 500 configured for use as an energy storage power source is a 12-pole, 108-stator slot / 90-rotor slot machine with three tertiary winding groups. The WRIM 500 includes a primary (stator) winding 502 wound 360 degrees around a stationary magnetic core 504. Stator slots 1-108 contain 12-pole, lap-wound, fully distributed, two-layer coils delta-connected with a conventional three-phase winding located at the bottom of the slot. This configuration has 3 slots / pole / phase. A secondary winding 506 is wound 360 degrees around a rotor magnetic core 508. Rotor slots 1-90 contain a delta-connected, lap-wound, 90-coil, fully distributed, three-phase winding, which is a conventional fractional slot winding with 2.5 slots / pole / phase. The number of turns per phase and the voltage are high. Three tertiary windings, T1 510, T2 512, and T3 514, are wound in diametrically opposed positions over a 2 x 60° circumferential angle and distributed around the fixed magnetic core 504. Stator slots 1-18 contain the first portion of tertiary winding T1, stator slots 19-36 contain the first portion of tertiary winding T2, and stator slots 37-54 contain the first portion of tertiary winding T3. The coil layout is repeated diametrically for all three windings as three-phase lap-wound, two-layer coils, each wye-connected with galvanic isolation between all groups. Each two-pole group is connected in parallel with two diametrically adjacent pole groups, for a total of four poles forming a 120-degree arc. The primary windings are located at the bottom of the slots, and the tertiary windings are located at the top of the slots. The 12-pole arrangement of the three tertiary windings is shown in Figure 5B.

[0062] Referring now to FIG. 6 , an embodiment of an energy storage power supply 600 includes a WRIM 602 having segmented primary windings 604A, 604B, ... 604F wound around a fixed magnetic core 605 and coupled to respective AC capacitor banks 606A, 606B, ... 606D. This configuration provides additional flexibility for simultaneously charging or discharging different ESEs (not shown) coupled to the WRIM's tertiary windings via a bidirectional three-phase AC / DC converter (not shown). In this example, there are six segmented primary windings, each magnetically coupled to two tertiary windings, for a total of 12 tertiary windings 610. In general, each primary winding segment may be coupled to any number of tertiary windings. At a given time, each pair or group of tertiary windings may be charging or discharging, but not both (e.g., XOR operation). However, different pairs of tertiary windings may be charging or discharging, and they are independent of each other. For example, the stator has 72 slots, and the segmented primary winding has 4 slots / pole / phase. Each tertiary winding has 2 slots / pole / phase. The rotor windings 612 are distributed around a 6-pole rotor magnetic core 614 with a total of 54 slots and 3 slots / pole / phase. A radial air gap 615 separates the rotor magnetic core 614 from the stationary magnetic core 605. This configuration allows the energy storage power supply to simultaneously charge or recharge certain ESEs while discharging other ESEs to provide energy to a load.

[0063] 7A-7D and 8A-8C, there are shown winding diagrams and design tables for a 12 pole 72 primary slot / 90 secondary slot WRIM with six tertiary winding groups.

[0064] As shown in FIG. 7A, the 12-pole primary (stator) winding 700 of a wound rotor induction motor has a total of 72 stator slots and 72 coils in the primary winding arranged for a three-phase input. Each phase has all coils connected in series for 24 coils per phase. There are two slots / pole / phase, meaning two coils are wound in the same direction for a set, and the winding direction alternates for the next two coils in a set. For example, coils 1 and 2 of phase A are wound clockwise, while coils 7 and 8 of phase A are wound counterclockwise in a repeatable pattern. In phase B, coils 5 and 6 are wound clockwise, and coils 11 and 12 are wound counterclockwise. In phase C, coils 3 and 4 are wound counterclockwise, and coils 9 and 10 are wound clockwise. The primary coils are evenly distributed around the circumference of the machine. Preferred coils are lap-wound and double-layered, as described in prior art machine literature. Typical conductor materials are either stranded insulated copper wire or stranded insulated aluminum wire. Each phase is terminated with a neutral connection, designated N, at a wye or star point. The invention is equally applicable when the coils are arranged in a delta configuration, as well as in two-phase or three- or more-phase configurations. In a preferred embodiment, the primary winding can be wound on the bottom layer of the stator slot, and the tertiary winding can be wound on the top layer.

[0065] As shown in Figure 7B, the 12-pole secondary (rotor) winding 702 has a total of 90 rotor slots and 90 coils in the secondary winding configured for a three-phase input. Each phase has two parallel groups with 15 coils per phase and group. There are 2.5 slots / pole / phase, which means two or three coils are wound in the same direction for a set, with the winding direction alternating for the next coil in the set. All coils may have the same number of turns and conductor cross-section. For example, coils 1, 2, and 3 ("south poles") are wound clockwise, while coils 9 and 10 ("north poles") are wound counterclockwise in a repeatable pattern. The secondary coils are evenly distributed 360 degrees around the machine rotor. Preferred coils are double-layered, either concentrically wound or lap-wound, as described in prior art machine literature. Typical conductor materials are either stranded insulated copper wire or stranded insulated aluminum wire. Each phase terminates in a delta connection. To access the three slip rings of the machine for excitation input, terminal A1 is connected to C2, terminal C1 is connected to B2 and terminal B1 is connected to terminal A2.

[0066] As shown in Figures 7C-7D, the six tertiary AC windings 704 of the primary electric machine are used to access the energy storage unit (ESE) through individual AC / DC power converters. Each of the six groups occupies two poles, or 60 degrees of stator slot circumference. There are 12 poles total. The block numbers in the diagram correspond to the actual tertiary coil numbers, connected as coils 1-72 arranged sequentially around the circumference. The preferred embodiment has a total of 72 stator slots. The coils are arranged in a wye configuration with two parallel groups per phase. Each group has a total of 12 coils, resulting in a design number of q = 2 slots / pole / phase since this is a three-phase winding. The number of turns per coil is not specified, as it depends on the exact type of energy storage unit used, such as an electrochemical battery or electrostatic capacitor. Generally, these coils are intended for low-voltage, high-current service. The preferred coils are lap-wound and double-layered, as described in prior art machine literature. Typical conductor materials are either stranded copper wire or stranded aluminum wire. Coils 1-18 and 19-36 are wound for "north poles," and coils 37-54 and 55-72 are wound for "south poles," thereby defining the relative directions of current flow to create the alternating magnetic field. The invention is equally applicable when the coils are arranged in a delta configuration, as well as in two-phase or three-or-more-phase configurations. A preferred embodiment has a tertiary winding that shares a common stator slot with the primary winding.

[0067] Design tables 800, 802, and 804 for a particular embodiment of the prime mover and primary (stator), secondary (rotor), and tertiary windings for a 12-pole, 72-stator / 90-rotor slot WRIM with six tertiary winding groups are shown in FIGS. 8A-8C.

[0068] As shown in FIG. 9 , in an alternative embodiment of the energy storage power supply 900, the WRIM 902 does not include a stator winding S or the stator winding S is not connected. One or more AC capacitor banks 904 are coupled to each tertiary winding 412 via vacuum circuit breakers 906 to magnetize the machine's air gap and compensate for the leakage reactance of the tertiary and secondary windings. If the ESE 426 includes series-connected supercapacitors, the AC capacitors 904 may minimize reactive current output because the bidirectional AC / DC converter 424 limits the amount of reactive current available at the AC terminals through thyristor gate delay angle control. If the ESE 426 includes series-connected electrochemical batteries, the AC capacitors 904 must be larger than in the previous case to provide more leading power factor reactive current for magnetization. For simplicity, similar elements are labeled with similar reference numerals from FIG. 4A . The one or more AC capacitor banks 904 provide leading power factor reactive power and balance lagging power factor reactive power, as previously described. The ESEs coupled to each AC capacitor bank 904 can be charged or discharged independently and simultaneously.

[0069] While several illustrative embodiments of the invention have been shown and described, numerous variations and alternative embodiments will occur to those skilled in the art. Such variations and alternative embodiments are contemplated and can be made without departing from the scope of the invention, as defined in the appended claims.

Claims

1. 1. An energy storage power source, comprising: a wound rotor induction motor (WRIM) including N tertiary windings each wound at 360 / N degrees around a first magnetic core, and a secondary winding wound 360 degrees around a second magnetic core and coupled to a load-generating output, the first and second magnetic cores being separated by a radial air gap and configured to rotate relative to one another; a shaft coupled to either the first magnetic core or the second magnetic core; a prime mover configured to rotate the shaft and power the WRIM; one or more AC capacitor banks coupled to either the primary winding wound 360 degrees around the first magnetic core or the tertiary winding; N energy storage elements (ESEs); N bidirectional AC / DC converters, each coupling one of the tertiary windings to a respective one of the energy storage elements; A WRIM controller, In a charging state, the prime mover rotates the shaft to magnetize the radial air gap with reactive excitation provided by the one or more AC capacitor banks to self-excite the WRIM, and the one or more AC capacitor banks provide leading power factor reactive power to balance lagging power factor reactive power required to magnetize the radial air gap and leakage inductance of the tertiary winding of the first magnetic core, and excite the tertiary winding to provide controlled power via the AC / DC converter to selectively charge the N ESEs; In a discharging state, at least a portion of the capacitances of the N ESEs are discharged through the AC / DC converter, exciting the tertiary winding to form a rotating magnetic field that magnetizes the radial air gap, providing active power to the second magnetic core, and individually contributing to the overall machine magnetic flux to magnetize the secondary winding, inducing an AC output voltage in the secondary winding that is proportional to the sum of the voltages from the discharging ESEs, and providing a portion of the N ESE energy capacitances as electrical energy to the load-generating output. a WRIM controller; Energy storage power source.

2. 2. The energy storage power supply of claim 1, wherein the WRIM includes the primary winding wound 360 degrees around the second magnetic core, and the one or more AC capacitor banks are coupled to the primary winding to magnetize the radial air gap and provide reactive compensation for leakage inductance of the primary winding.

3. 3. The energy storage power source of claim 2, wherein the primary winding is segmented into M primary windings, each primary winding is coupled to a different one of the AC capacitor banks, reactive current circulates between the primary winding and a respective capacitor bank, each primary winding is magnetically coupled to one or more of the tertiary windings, and the WRIM controller simultaneously charges one or more ESEs coupled to a first subset of the M primary windings and discharges one or more ESEs coupled to a second subset of the M primary windings, the first and second subsets being non-overlapping.

4. 10. The energy storage power supply of claim 1, wherein a plurality of said AC capacitor banks are coupled to a respective plurality of tertiary windings.

5. 5. The energy storage power source of claim 4, wherein the WRIM controller is configurable to independently charge or discharge the ESEs coupled to different tertiary windings and AC capacitor banks.

6. 2. The energy storage power supply of claim 1, wherein the AC output voltage of the secondary winding is scaled by a transformation ratio determined by a turns ratio of the secondary winding to the N tertiary windings.

7. 7. The energy storage power supply of claim 6, wherein the conversion ratio is greater than 1:1, on average, for all N ESEs to increase the AC output voltage.

8. 2. The energy storage power source of claim 1, wherein the load-generating output is configured for bidirectional flow of energy, and the WRIM is configured to selectively receive energy from the load-generating output to charge the ESE.

9. 9. The energy storage power source of claim 8, further comprising: a flywheel coupled to the shaft, the flywheel configured to selectively store energy from the prime mover, the ESE, or the load-generating output via the secondary winding, and to selectively supply energy to at least the ESE and the load-generating output via the secondary winding.

10. The energy storage power source of claim 1 , wherein the N ESEs are electrically isolated from each other.

11. 2. The energy storage power source of claim 1, wherein the N bi-directional AC / DC converters are independently controllable to exclusively selectively charge one or more ESEs or independently controllable to selectively discharge (XOR) the one or more ESEs.

12. 10. The energy storage power supply of claim 1, further comprising: a load power factor controller coupled to the load generating output to modulate an inductive-resistive load and actively adjust the power factor of the WRIM to vary the rotational speed of the shaft and maintain the AC output voltage of the secondary winding within a specified tolerance of a target voltage.

13. 10. The energy storage power source of claim 1, further comprising a flywheel coupled to the shaft for storing energy and supplying kinetic energy to the ESE, the load-generating output, or maintaining or accelerating the rotation of the shaft.

14. 14. The energy storage power supply of claim 13, wherein the WRIM controller is configured to discharge one or more ESEs to supply energy to the load-generated output with a first discharge time constant and decelerate the flywheel to supply energy to the load-generated output with a second discharge time constant, the second discharge time constant being longer than the first discharge time constant.

15. 15. The energy storage power source of claim 14, wherein the WRIM controller is configured to charge one or more ESEs at a first charging time constant and to accelerate and charge the flywheel to store energy at a second charging time constant, the second charging time constant being shorter than the first charging time constant, the WRIM being capable of storing energy in the flywheel, and the prime mover ESE having a designated peak power being capable of supplying energy to the load generating output at a transient peak power greater than the designated peak power.

16. The energy storage power source of claim 1 , wherein in the discharge state, the WRIM controller is configured to selectively decouple the prime mover from the shaft.

17. 2. The energy storage power supply of claim 1, wherein in the discharge state, the WRIM controller is configured to keep the prime mover coupled to the shaft and supply additional energy to the load-generating output via the secondary winding.

18. 10. The energy storage power supply of claim 1, wherein a rotor assembly includes a secondary winding wound around a second magnetic core, and a stator assembly includes a primary winding wound around a first magnetic core, two said rotor assemblies connected to said shaft or to said prime mover, each rotor assembly operating within a separate stator assembly, each stator assembly having separate ESEs N1 and N2 and tertiary windings N1 and N2, and magnetically coupled to two or more independent load generating outputs.

19. 1. An energy storage power source, comprising: a wound rotor induction motor (WRIM) including a primary winding wound 360 degrees around a fixed magnetic core, a secondary winding wound 360 degrees around a rotating magnetic core separated from said fixed magnetic core by a radial air gap and coupled to a load generating output, and N tertiary windings each wound at 360 / N degrees around said fixed magnetic core, wherein the turns ratio i=1 to N of the number of secondary turns Ns and the number of tertiary turns Nt(i) defines an average step-up conversion ratio greater than 1; a rotor shaft coupled to the rotating magnetic core; a flywheel coupled to the rotor shaft; a prime mover configured to rotate the rotor shaft and power the WRIM; an AC capacitor bank coupled to the primary winding; N energy storage elements (ESEs); N bidirectional AC / DC converters, each coupling one of the tertiary windings to a respective one of the energy storage elements; A WRIM controller, In one or more charging states, the prime mover rotates the rotor shaft to magnetize the radial air gap with reactive excitation provided by the AC capacitor bank to self-excite the WRIM, the AC capacitor bank providing leading power factor reactive power to balance lagging power factor reactive power required to magnetize the radial air gap and leakage inductance of the primary and tertiary windings of the fixed magnetic core, and exciting the tertiary winding to provide controlled power via the AC / DC converter to selectively charge the N ESEs and generate torque to charge the flywheel; In one or more discharge states, the capacitance of at least a portion of the N ESEs discharges back through the AC / DC converter, excites the tertiary winding to generate a rotating magnetic field, magnetizes the radial air gap to provide actual power to the rotating magnetic core, and individually contributes to a total mechanical flux to magnetize the secondary winding to induce an AC output voltage in the secondary winding proportional to the sum of the voltages from the discharging ESEs multiplied by their respective step-up transformation ratios, and provides a portion of the energy capacitance of the N ESEs as electrical energy to the load-generating output, or the flywheel discharges energy through the secondary winding to the load-generating output. a WRIM controller; Energy storage power source.

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