| Method and system for transformer control -> Monitor Keywords |
|
|
 
Method and system for transformer controlMethod and system for transformer control description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080024114, Method and system for transformer control. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001]The present disclosure relates generally to power conversion, and particularly to transformer control. [0002]Transformers are used to convert between high and low voltages, to change impedance, and to provide electrical isolation between circuits. In a transformer, an alternating current in one winding creates a time-varying magnetic flux in the core, which induces a voltage in the other windings. A group of transformers may be connected together to provide specific operating characteristics. [0003]Imbalance of transformer flux among the group of transformers may result in the generation of a flux direct current (DC) offset. In a perfect environment, it is preferable that transformers not be driven with DC nor, generally, have any DC component present at the input. Relatively small amounts of DC can cause core saturation, current distortion, and increased losses, thereby preventing proper operation. Also, because a DC voltage source does not provide a time-varying flux in the core, an induced counter-EMF is not generated, resulting in current flow into the transformer that is limited only by the series resistance of the transformer windings. In this situation, the transformer would heat until it either reaches thermal equilibrium or is possibly damaged. [0004]One cause of core saturation is the accumulation of low frequency flux, such as when a motor is starting, for example. Another cause of flux saturation within series connected transformers is flux imbalance among the different transformers, which may result from disturbances within the grid and variation among transformer parameters or switching patterns. Flux balance control is generally implemented by controlling the average value of transformer flux to be zero. This will involve the moving-average calculation of flux. However, during very low frequency operation, such as motor startup, the delay caused by the average flux calculation is too large, making it difficult to control the flux balance within an acceptable period. Accordingly, there is a need in the art for a transformer arrangement that overcomes these drawbacks. BRIEF DESCRIPTION OF THE INVENTION [0005]An embodiment of the invention includes a method to balance transformer flux among a plurality of transformers. The plurality of transformers is connected to a plurality of converters, each transformer having an associated converter. The method comprises determining a reference flux value, measuring an actual flux value for each transformer, and developing a plurality of voltage command signals in relation to a plurality of variance values between the reference flux value and each actual flux value. In response to the voltage command signals being received at a modulator in signal communication with the plurality of converters, the method proceeds by generating a plurality of switching signals to reduce each of the variance values by making available the plurality of switching signals to each of the associated plurality of converters. [0006]Another embodiment of the invention includes a control system to balance transformer flux among a plurality of transformers connected to a plurality of converters. The system includes a flux estimator configured to estimate a reference flux value, and a plurality of flux monitors in signal communication with each transformer, each flux monitor configured to measure an actual flux value of each transformer. A plurality of flux comparators is in signal communication with the flux estimator and each flux monitor, the plurality of flux comparators configured to determine a plurality of variance values between the reference flux value and each actual flux value. A plurality of flux regulators is in signal communication with each of the flux comparators, the plurality of flux regulators configured to develop a plurality of voltage command signal responsive to each variance value. A modulator is in signal communication with the plurality of flux regulators and the plurality of converters, the modulator responsive to each voltage command signal and configured to generate and make available a switching signal to each converter, wherein the switching signal is configured to reduce each variance value. BRIEF DESCRIPTION OF THE DRAWINGS [0007]Referring to the exemplary drawings wherein like elements are numbered alike in the accompanying Figures: [0008]FIG. 1 depicts a block schematic diagram of a motor drive system utilizing a flux balance controller in accordance with an embodiment of the invention; [0009]FIG. 2 depicts a block schematic diagram of a motor-side transformer flux controller in accordance with an embodiment of the invention; and [0010]FIG. 3 depicts a block schematic diagram of a grid-side transformer flux controller in accordance with an embodiment of the invention; [0011]FIG. 4 depicts a block schematic diagram of a signal conditioner in conjunction with a multi-pulse modulator in accordance with an embodiment of the invention; [0012]FIG. 5 depicts a block schematic diagram of a signal conditioner in conjunction with a pulse-width-modulation modulator in accordance with an embodiment of the invention; and [0013]FIG. 6 depicts a flowchart of an exemplary method to balance flux among a set of transformers in accordance with an embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION [0014]An embodiment of the invention provides a method to control the flux balance of series connected transformers that are controlled by power electronic converters. The method will mitigate the flux DC offset to avoid transformer saturation at both low and high frequency operation. [0015]An embodiment of the invention will also reduce unnecessary current stress when the output voltage is to be delivered through transformers and the net voltage requires to be minimally affected by the transformer magnetizing current. In an embodiment, an instantaneous reference flux value is determined from a motor flux (or a grid voltage that is connected to the transformers), and is compared with the instantaneous actual flux of each transformer. A regulator output is sent to a modulator, together with a normal current regulator output, to directly control the instantaneous flux for each transformer. [0016]To balance flux among transformers associated with the grid, the goal is to evenly distribute the supply voltage to avoid any flux DC offset of any one of the transformers. To balance flux among transformers associated with a drive, such as a motor for example, the motor stator flux is evenly distributed among the transformers. Or, if there is at least one converter configured to feed directly to the motor without a transformer, performance can be enhanced if this converter supports the IR (current times resistance) drop of the motor. [0017]In an embodiment, a regulator, such as a proportional-integral controller, for example, provides a signal to a converter modulator, which is used to control the transformer instantaneous flux in a static reference frame, such as an alpha-beta two-phase representation, or an ABC three-phase, for example, to the reference value. Because the bandwidth of the regulator is independent of the electrical frequency of motor and the grid, it is suitable for control of the variable frequency motor, and therefore allows transformer flux to be balanced at low frequency operation, such as during motor ramp up to nominal speed. [0018]Referring now to FIG. 1, an embodiment of a motor drive system 100 is depicted. The motor drive system 100 connects to a grid (labeled "Grid") 200, and comprises a load (also herein referred to as a motor) 300, a plurality of converters 210, a plurality of transformers 220, and a flux balance controller 400. Reference numerals 211 and 221 will be used herein to refer, respectively, in general, to a single converter of the plurality of converters 210, and a single transformer of the plurality of transformers 220. In an embodiment, the plurality of transformers 220 consists of a first set of transformers 227 associated with the motor 300, and a second set of transformers 222 associated with the grid 200. [0019]In an embodiment, the first set of transformers 227, associated with the motor 300, are connected in series, and the second set of transformers 222, associated with the grid 200, are connected in series. In an embodiment, the transformers 220 are three phase transformers. In an embodiment, the flux balance controller 400 is in signal connection with each transformer 221, each converter 211, and the motor 300. It will be appreciated that for the purposes of clarity of illustration, the flux balance controller 400 may be considered to comprise a motor-side transformer flux controller 405, and a grid-side transformer flux controller 450, as will be described further below. [0020]Referring now to FIG. 2, an exemplary embodiment of the motor-side transformer flux controller 405 for controlling the flux associated with the first set of transformers 227 associated with the motor 300 is depicted. A module 406, associated with one of the transformers 221 of the first set of transformers 227 is depicted in enlarged view. It will be appreciated that each module 406 of a set 407 of modules 406 includes similar components as described below. Continue reading about Method and system for transformer control... Full patent description for Method and system for transformer control Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method and system for transformer control patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Method and system for transformer control or other areas of interest. ### Previous Patent Application: System of phenon spectroscopy Next Patent Application: Printed circuit board connector for utility meters Industry Class: Electricity: measuring and testing ### FreshPatents.com Support Thank you for viewing the Method and system for transformer control patent info. IP-related news and info Results in 0.10408 seconds Other interesting Feshpatents.com categories: Qualcomm , Schering-Plough , Schlumberger , Seagate , Siemens , Texas Instruments , 174 |
 * Protect your Inventions * US Patent Office filing 
PATENT INFO |
|
