WO2010092580A1

WO2010092580A1 - Accurate frequency regulation for uninterruptible electric power supply

Info

Publication number: WO2010092580A1
Application number: PCT/IL2010/000130
Authority: WO
Inventors: Abraham Liran
Original assignee: Flywheel Energy Ltd.
Priority date: 2009-02-16
Filing date: 2010-02-14
Publication date: 2010-08-19

Abstract

Device, system and method for providing continuously stable AC mains power to sensitive loads by smoothing out frequency and voltage fluctuations and interruptions. A synchronous Generator is propelled by a gas or fuel engine via an overrunning clutch. The voltage and frequency of the generator output are continuously monitored. A rotating flywheel is continuously propelled by an electric motor in order to maintain high kinetic energy, which is stored in the flywheel rotating mass. When output frequency drop in sensed, a Control Processor initiates a "magnetic friction" between the flywheel and the Synchronous Generator's shaft in order to accelerate it, thus mounting the output frequency toward its nominal value. Conversely, when the Synchronous Generator output frequency is measured to be too high, e.g due to an abrupt drop of the generator loading, the Control Processor initiates an inverse "magnetic friction" between the synchronous Generator's shaft and a Brake Support, which slows the generator down to conform to the nominal output frequency.

Description

Title: ACCURATE FREQUENCY REGULATION FOR UNINTERRUPTIBLE ELECTRIC POWER SUPPLY

FIELD OF THE INVENTION

[001] The present invention relates generally to a system and a method of supplying uninterrupted and regulated electric power to sensitive loads that require a very stable mains supply.

BACKGROUND OF THE INVENTION

[002] Computers and other sensitive equipment used for applications such as data communication, data processing, precise computation and imaging, demand an uninterrupted and stable mains power. To achieve this, power backup and regulation systems are required for supplying high quality regulated mains power whenever the utility power either fluctuates or fails. In particular, the above applications can withstand very small frequency fluctuations, typically smaller than +/- IHz.

[003] When a gas or diesel engine is used to rotate a backup electric generator in order to produce and supply electric power to a load, the amount of consumed gas or fuel is relative to the magnitude of the load power. When the supplied power is small, the required amount of gas or fuel is small and when the load power increases the required gas or fuel shall increase correspondingly in order to maintain the nominal output voltage and frequency of the electric generator. However, there is a response time delay from the moment of load power changes until the time that the engine control loop adjusts to the exact fuel or gas consumption rate needed to sustain the actual load power. During this time delay, the voltage and frequency that are supplied to the load would deviate from the nominal values, which may be harmful to the load. For such applications, a power regulation system that is capable of correcting the electric power fluctuations is required.

[004] One of the existing methods to stabilize the supplied power is to use capacitors and rechargeable batteries. However, these solutions are very expensive and inefficient for power supplies of above 350 KW. [005] British patent 1309858 discloses a power supply method and a system for ensuring uninterrupted power supply to the load. This method provides partial compensation for voltage drops by connecting an auxiliary power supply to the load via a secondary winding of a transformer. The primary winding of the transformer is connected to a choke located between the utility power and the supply. This kind of machine requires Batteries and a DC to AC electronic inverting. For high power applications, above 300 KVA this approach is very expensive, unreliable and requires a large Batteries space.

[006] EP patent 69568 discloses an uninterrupted power supply method wherein a high frequency alternating current (AC) power generator drives a small, high-speed motor and a flywheel that are both located in a sealed chamber. This approach is relatively expensive due to the use of an additional high frequency generator and complex electronics. Moreover, maintaining accurate output frequency and phase is problematic in this configuration.

[007] U.S. patents 4827152, 5311062 and 5434454 disclose uninterrupted power supplies using a high-pressurized hydraulic system. These systems are unreliable since the high pressure piping included in these systems might burst. Moreover, these systems do not provide the accurate output frequency immediately after the utility power drop due to the need to accelerate the hydraulic motor at the utility outage instant.

[008] U.S. patent 6020657 discloses an uninterrupted power supply using 3 phase AC motors to turn the flywheel, wherein at the instant of utility power drop the AC motor becomes an Electromagnetic Clutch by switching two phases. This kind of clutch is not efficient and requires too much power to produce the required torque.

[009] U.S. Patent 6204572 is similar to the previous patent' except that instead of using an AC motor as a clutch between the flywheel and the "synchronous machine", it uses a combination of induction coils and induction bars facing each other axially. This kind of clutch generates axial forces between the "synchronous machine" and the flywheel, which implies quite a large gap between the two parts of the clutch. The resulting clutch efficiency is quite low and special expensive bearings are required to carry the axial forces. Moreover, the system reliability is compromised because it is impossible to rotate the flywheel using a direct drive.

[0010] Besides the above mentioned drawbacks of either low reliability or low cost effectiveness, the technology that is available to date in the field of the invention does not teach or suggest how to efficiently prevent frequency fluctuations of a power generator that is propelled by a gas or fuel engine. Such fluctuations may result due to abrupt load variations, and the present technology especially fails to compensate for abrupt drops in the load impedance.

SUMMARY OF THE INVENTION

[0011] The present invention overcomes the drawbacks of the background art by providing a continuously stable AC mains power to sensitive loads by smoothing out frequency and voltage fluctuations and interruptions as hereby described. The load is normally connected to a utility AC mains power source, and the voltage and frequency of the utility source are continuously measured by V/F sensors. When the V/F sensors indicate that either the utility voltage or the utility frequency deviate from their nominal values, and the deviation exceeds an allowed value, a computer based Control Unit disconnects the load from the utility source and connects it to a backup system.

[0012] First embodiment of the backup system is based on a Synchronous Generator that is propelled by a gas or fuel engine via an overrunning clutch. The voltage and frequency of the generator output are continuously measured by a second set of V/F sensors. The backup system further comprises a rotating flywheel that is continuously propelled by an electric motor in order to maintain high kinetic energy, which is stored in the flywheel rotating mass.

[0013] When the backup system is connected to the load the engine is turned on by the Control Processor. Its rate of revolutions, which determines the output power frequency, is lower than the nominal frequency value during its startup period. The output frequency might also decrease due to an abrupt loading increase. When such output frequency drop is measured by the frequency sensor, the Control Processor initiates a "magnetic friction" between the flywheel and the Synchronous Generator's shaft in order to accelerate it, thus mounting the output frequency toward its nominal value.

[0014] Conversely, when the Synchronous Generator output frequency is measured to be too high, e.g. due to an abrupt drop of the generator loading, the Control Processor initiates an inverse "magnetic friction" between the Synchronous Generator's shaft and a Brake Support, which slows the generator down to conform to the nominal output frequency. [0015] A second embodiment of the invention comprises two backup sections A and B. Section B constitutes a Standard integrated backup system that comprises a gas or fuel engine which propels a Synchronous Generator. Section A is basically the same as described in the first embodiment, but without the engine and the Overrunning clutch. In this embodiment Section A is intended to smooth out fluctuations and short outage periods of section B backup system.

[0016] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The materials, methods, and examples provided herein are illustrative only and not intended to be limiting.

[0017] According to actual instrumentation and equipment of preferred embodiments of the method and system of the present invention, several selected stages could be implemented by hardware or by software on any operating system of any firmware or a combination thereof. For example, as hardware, selected stages of the invention could be implemented as a chip or a circuit. As software, selected stages of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system. In any case, selected stages of the method and system of the invention could be described as being performed by a data processor, such as a computing platform for executing a plurality of instructions.

[0018] Although the present invention is described with regard to a "Control Processor" it should be noted that optionally any device featuring a data processor and/or the ability to execute one or more instructions may be described as a Control Processor, including but not limited to a PC (personal computer), a server and a minicomputer.

BRIEF DESCRIPTION OF THE DRAWINGS

[001] The invention is herein described, by way of example only, with reference to the accompanying drawings. 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 order to provide 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. [0019] In the drawings:

[0020] Fig. 1 depicts a schematic diagram of a first embodiment of the invention. [0021] Fig.2 depicts a schematic diagram of a second embodiment of the invention, which constitutes an enhancement of a standard backup system.

[0022] Fig. 3 depicts a mechanical diagram of first and second embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0023] Fig. 1 depicts a schematic diagram of a first embodiment of the invention. During normal operation Switch [2a] is closed in order to transfer mains 3 phase AC power from Utility Power source [1] to Load [3]. Switch [2b] is closed in order to transfer an electric power to Section A [30a] of the invention system. Synchronous Generator [12] operates in this mode as an electric motor and rotates Electromagnetic Transmission Wheel [8]. Electric motor [9] rotates Flywheel [1 Ia] via rotational Coupling [10b] in a rotation rate of e.g. 1500 RPM, which is much higher than the nominal mains frequency. The high rotation loads the flywheel mass with a kinetic energy. V/F Sensor [5a] constantly measures the voltage and frequency of the Utility Power and transfers the measured values to Control Processor [4].

[0024] As shown in Fig. 1, Induction Bars [8f ] are a series of ferromagnetic bars that are sunk into and fill a circular groove that is grooved on the surface of Electromagnetic Transmission Wheel [8]close to its circumference. Between any pair of adjacent ferromagnetic bars there is a separator bar of non magnetic material. Air Gap [16b] separates between Induction Bars [8f] to Magnetic Coil [15c]. This coil is a made of a conductive winding that is wound along and inside a circular groove that is grooved on the surface of Brake Support [15] close to its circumference. Similarly, Induction Bars [1 Ib] and Magnetic Coil [8b] are located at both sides of Air Gap [16a] in circular grooves close to the circumferences of Flywheel [1 Ia] and Electromagnetic Transmission Wheel [8] correspondingly.

[0025] Primary Winding [15a] and Secondary Winding [8c] are circular coils that face each other through Air Gap [16b] and encapsulated within Laminations [15b] and [8d] correspondingly. The laminations are "C" shaped magnetic conductive sheet metals which are sunk into and fill circular grooves on the surfaces of Brake Support [15] and Electromagnetic Transmission Wheel [8] correspondingly.

[0026] When V/F Sensor [5a] measures either a voltage drift or a frequency drift of Utility Power [1] that exceed a predefined thresholds, e.g. 5 V and 0.5Hz correspondingly, Control Processor [4] immediately opens Switch [2a] and starts up Diesel Engine [14]. Consequently, after a certain response delay, Diesel Engine will propel Synchronous Generator [12] via Overrunning Clutch [13] and as a result the generator will supply power to Load [3] via Switch [2b]. No phase transient would result over Load [3] because the stator's voltage of synchronous machine [12] has been in phase with Utility Power before its transition from motor mode to generator mode.

[0027] The output voltage of the generator is internally regulated by a built in excitation current control loop, which is an integral part of Synchronous Generator [12]. The output frequency of the generator is equal to the rotation rate of its shaft and rotor and would have been too low, hence harmful to the load, had it been determined by Diesel Engine [14] during its startup response delay period.

[0028] In order to ensure nominal frequency of the power that is supplied to the load during the response delay of the engine, the invention mechanism immediately rotates the generator shaft at nominal rate by applying the following control loop: Control Processor [4] instructs VARIAC [6] to apply AC power to Primary Winding [15b] which is located on Brake Support [15]. Primary Winding induces an alternating magnetic flux in Secondary Winding [8d], which is located on Electromagnetic Transmission Wheel [8], via Air Gap [16b]. The AC voltage that is generated on the secondary winding is converted to DC voltage by a two diode Rectifier [8a]. The rectifier output DC voltage is applied on Magnetic Coil [8b]. Both Rectifier [8a] and Magnetic Coil [8b] are located on [8]. Magnetic Coil [8b] induces a constant magnetic flux on Induction Bars [1 Ib], which are located on Flywheel [1 Ia], via Air Gap [16a]. The resulting pulling force between the Magnetic Coil and the Induction Bars results in a magnetic friction between fast rotating Fly Wheel [Ha] and Electromagnetic Transmission Wheel [8]. This friction immediately results in rotation of Electromagnetic Transmission Wheel [8]. Electromagnetic Transmission Shaft [8e] transfers the resulting torque to Synchronous Generator [12] via rotational Coupling [1Oa]. Consequently, the output frequency of the generator increases. V/F sensor [5b] measures this frequency and transfers the measured value to Control Processor [4]. [0029] Control Processor [4] is programmed to implement a controlled FLL (Frequency Locked Loop) over the described above system loop. The target of the FLL is to lock the generator frequency on the nominal mains frequency, e.g. 60 Hz. The control loop has a "dead zone" around the nominal frequency that is equal to the total frequency inaccuracies in the system, in particular Diesel Engine [14] inaccuracy. The rationale for this is to avoid a contention between the internal FLL of Diesel Engine, which may try to lock on e.g. 60.1 Revolutions Per Second, and the system FLL, which may try to lock on e.g. 59.99 Hz.

[0030] A need to accelerate the generator rotation rate may arise also beyond the engine's startup stage, e.g. if the load impedance abruptly decreases, which would result in a temporal frequency drop. Conversely, if the load impedance abruptly increases, a temporal frequency rise would result, and the FLL shall temporally slow down the generator rotation rate. The slow down loop differs from the described above acceleration loop as follows: Control Processor [4] turns VARIAC [6] off and turns DC Power Supply [7] on. Its output current flows through Magnetic Coil [15c], which is located on Brake Support [15], and results in a constant magnetic flux around it. The magnetic flux applies a pulling force on Induction Bars [8f], which are located on the rotating Electromagnetic Transmission Wheel [8], via Air Gap [16b]. The resulting magnetic friction between Wheel [8] and Brake Support [15], which is connected to the system mechanical Frame [20], would slow down the wheel rotation rate, hence the generator rotor rotation rate, thus locking it on the nominal main frequency.

[0031] When Synchronous Generator [12] feeds Load [3], Control Processor [4] keeps monitoring Utility Power [1] via V/F [5a]. When it senses that Utility Power has resumed stable mains nominal V/F within the inaccuracy range of the system, it closes Switch [2a] at the moment of phase match between Fl and F2 and simultaneously turns off Diesel Engine [14] and cuts off the above FLL loop if it happens to be active.

[0032] Switch [2b] is opened only when the invention system is first connected to Utility Power [I]. Control Processor [4] then accelerates Synchronous Generator [12] as described above, while Diesel Engine [14] is shut down. When the generator reaches the exact frequency and phase of the Utility Power, Control Processor simultaneously opens the acceleration loop by zeroing DC Power supply [7], and closes Switch [2b]. [0033] Chock [21] is an optional member that is intended to protect the system against fast transients of Utility Power [I]. In particular, it would avoid shutdown of the system in case that the Utility Power abruptly falls to zero voltage at very low output impedance.

[0034] Fig. 2 depicts a second embodiment of the invention that is intended to improve the quality of the main power that is supplied by an existing standard backup power system. The existing backup system is depicted by Section B [30b] block and comprises Diesel Engine [14] that propels Synchronous Generator [12a]. Section A [30a] is identical to Section A of Fig. 1.

[0035] When Control Processor [4] detects an excess either voltage or frequency deviation of Utility Power [1] it opens Switch [2a] and rotates Synchronous Generator [12] as explained above to avoid mains power interruption to Load [3]. Control Processor concurrently starts up Diesel Engine [14] and monitors the frequency and phase of Synchronous Generator [12a] by means of F3 sampling signal. When those are equal to the frequency and phase of Synchronous Generator [12], Control processor simultaneously closes Switch [2c] and cut off the drive loop of Synchronous Generator [12]. Out of this point Section A system would smooth out any fluctuations of Section B as explained above regarding to Utility Power fluctuations.

[0036] The lower part of each one of the following members is illustrated in Fig. 1:

Electromagnetic Transmission Wheel [8], Flywheel [l la], Flywheel support [11] and Brake support [15]. Fig. 3 depicts a full mechanical diagram of the invented system in cross section view. The left part of the diagram contains Diesel Engine [14] and Overrunning Clutch [13]. This part is included in the first embodiment, which is depicted in Fig. 1, and is excluded from the second embodiment, which is depicted in Fig. 2.

[0037] As illustrated in Fig. 3 Electromagnetic Transmission Wheel" [8] is attached to

Brake Support [15] through a set of Bearings [18a]. Its inner circumference is attached to one side of the shaft of Flywheel [1 Ia] through a set of Bearings [18c] and [18e]. The opposite side of the Flywheel shaft is attached through two sets of Bearings [18f] and [18d] to Cylinder [17]. Cylinder [17] is supported by Flywheel Support [11] through Bearings [18b].

[0038] Bearing [18a] to [18f] are preferably ball bearings such as SKF bearing 6036, which are capable of bearing radial loads as well as axial loads. Other kinds of bearings may be used as well, including magnetic and electromagnetic bearings, oil or air bearings. Flywheel [10a] shall be preferably made of steel or alloy steel.

Claims

What is claimed is:

1. A system for supplying a stable AC mains power to a load, comprising: a first sensor that measures the voltage and the frequency of a utility power source, a first switch that connects said load and the other parts of the system to said utility, a synchronous generator that is normally connected to said load, a flywheel that rotates in much higher rate than said generator, a motor that propels said flywheel, a second sensor that measures the frequency of the AC power that is supplied to said load, a driving electromagnetic transmission that is connected between said flywheel to the rotor shaft of said synchronous generator and can accelerate the rotation of said rotor by transferring part of the kinetic energy that is stored in said flywheel to said rotor, a braking electromagnetic transmission that is connected between said rotor shaft to a braking support and can slow down the rotation of said rotor by pulling it toward said braking support, and a control processor that constantly reads out the measurements of said first sensor and said second sensor and can control said first switch, said driving electromagnetic transmission and said braking electromagnetic transmission; and a method for stabilizing the voltage and the frequency that is supplied to said load that comprises the following steps: whenever said control processor reads out on said first sensor either a voltage deviation or a frequency deviation from the nominal said utility voltage and frequency values correspondingly that exceeds a predefined allowed deviation value it opens said first switch and either: commands said driving electromagnetic transmissions to accelerate the rotation rate of said rotor whenever the frequency that it reads on said second sensor is lower than a predefined lower threshold, or commands said braking electromagnetic transmission to slow down the rotation rate of said rotor whenever the frequency that it reads on said second sensor is higher than a predefined upper threshold, and whenever said control processor reads out on said first sensor that both said utility voltage and frequency deviations from their nominal values are lower than predefined allowed values it simultaneously cuts off said electromagnetic transmissions and closes said first switch.

2. The method and system of claim 1 , wherein the driving electromagnetic transmission comprises: a variable AC supply that is fed by said load voltage and is controlled by said control processor; a circular primary winding that is fed by said variable AC supply and is encapsulated in ferromagnetic laminations that are sunk inside a groove on the surface of a mechanical

"brake support"; an "electromagnetic transmission wheel" that its first surface faces said brake support via first air gap and its axis is connected to the shaft of said synchronous generator; a circular secondary winding that is encapsulated in ferromagnetic laminations that are sunk inside a circular groove on the first surface of said electromagnetic transmission wheel and faces said primary winding via said first air gap, wherein the current through said primary winding induces proportional current on said secondary winding; a rectifier located on said electromagnetic transmission wheel that converts said induced current to a DC current that is applied on a magnetic coil, wherein said magnetic coil is wound inside a circular groove on the second surface of said electromagnetic transmission wheel; and a set of ferromagnetic induction bars that are stuck into a circular groove on the surface of said flywheel, facing said magnetic coil via said second air gap; wherein the effect of the magnetic field of said magnetic coil on said induction bars result in a pulling electromagnetic force between said induction bars and said electromagnetic transmission wheel that accelerate said synchronous generator via their common shaft.

3. The method and system of claim 1. 1 that further comprise a second switch for connecting said synchronous generator to said utility source and said load, wherein said second switch is open only when the system is first activated and the following startup steps are commanded by said control processor: said synchronous generator is accelerated by said driving electromagnetic transmission, the frequency and phase of said utility source and said synchronous generator are constantly measured by said first and second sensors correspondingly and read out by said control processor, and when an exact frequency and phase match is achieved said control processor simultaneously closes said second switch and cuts off said electromagnetic transmission.

4. The method and system of claim 1. 1, wherein said flywheel is propelled by an electric motor.

5. The method and system of claim 1, wherein said control processor closes said first switch, in order to resume said utility power supply to said load, at the moment when the phase shift between said utility voltage and said synchronous generator, as read out by said control processor at the output of said first and second sensors, has reached zero.

6. The method and system of claim 1 that further comprise a backup engine and an overrunning clutch, wherein said engine propels said synchronous generator via said overrunning clutch, and controlled by said control processor according to the following steps: said engine is turned on by said control processor whenever said first switch is opened, said overrunning clutch enables fast rotation of said synchronous generator by said driving electromagnetic transmission until the rotation rate of said engine adheres the rotation rate of said driving electromagnetic transmission,

Said control processor turns off said engine whenever it closes said first switch thus resuming said utility power supply.

7. The method and system of claim 1 that further comprise a chock, wherein said utility source is connected to the invention system and to said load via said chock in order to protect the load and the invention system against fast transients of said Utility, and in particular to avoid shutdown of the invention system in case that said utility abruptly falls to zero voltage at very low output impedance.

8. The method and system of claim 1 that further comprise: a backup engine, a second synchronous generator that is directly propelled by said engine, a third switch that connects said second synchronous generator to said load and a third sensor that constantly measures the output voltage and the frequency of said second synchronous generator and transfer its reading to said control processor, wherein said control processor turns on said backup engine whenever said utility fails, and simultaneously closes said third switch and turns off said driving electromagnetic transmission at the moment that the frequency and phase of said second synchronous generator match those of said synchronous generator.

9. The method and system of claim 2, wherein the braking electromagnetic transmission comprises: a variable DC power supply that is fed by said load voltage and is controlled by said control processor; a second circular magnetic coil that is stuck in a groove on the surface of said brake support; a second set of ferromagnetic induction bars that is stuck inside said first surface of said electromagnetic transmission wheel; wherein the magnetic field that is applied on said induction bars through said first air gap generates a pulling electromagnetic force between said second magnetic coil and said second set of induction bars that would slow down said electromagnetic transmission wheel, thus slowing down said synchronous generator via their common shaft;

10. The method and system of claim 6, wherein the engine can run on energy from a variety of sources such as diesel, gas, fuel, wind, water and geothermal.

11. The method and system of claim 6, wherein the invention system functions in standalone mode, i.e. no utility power source is used.