CLIAMS:We Claim:

1. A degaussing unit to deliver a programmable bipolar constant current for a degaussing coil, said unit comprising:
a digital signal processor configured to determine duty cycle of gate pulses to control output current and direction of said current based on voltage and current feedback from load and further based on input from a system controller;
one or more switching MOSFETs that chop input DC supply based on said gate pulses, wherein said one or more switching MOSFETs comprise one or more high voltage switching MOSFETs and one or more low voltage switching MOSFETs, wherein said high voltage switching MOSFETs are used when output current requirement is above a defined threshold, and said low voltage switching MOSFETs are used when output current requirement is below said defined threshold.
2. The degaussing unit of claim 1, wherein said one or more high voltage MOSFETs are switched in a staggering manner to reduce switching losses and lower heat generation.
3. The degaussing unit of claim 1, wherein said system controller is remotely located, and wherein said digital signal processor receives said input from said system controller through a first Ethernet connection.
4. The degaussing unit of claim 1, wherein said degaussing unit incorporates a second Ethernet connection for connectivity to a local computing device for local control and debugging.
5. The degaussing unit of claim 1, wherein said degaussing coil has resistance in the range of 0.5Ω to1.75Ω, and inductance in the range of 5 to 100 mH.
6. The degaussing unit of claim 1, wherein power source for said degaussing unit is a 68Vdc to 110Vdc remote transformer rectifier unit (TRU).
7. The degaussing unit of claim 1, wherein said output current is limited within a range of -30.5A to +30.5A irrespective of current demanded by said system controller and load impedance.
8. The degaussing unit of claim 1, wherein said degaussing unit further comprises four additional MOSFETs connected in a ‘H’ bridge configuration for change in direction of output current.
9. The degaussing unit of 8, wherein said one or more switching MOSFETs and said additional MOSFETs have low resistance in linear region.
10. The degaussing unit of claim 1, wherein said degaussing unit further comprises a LC filter to reduce switching noise.
11. The degaussing unit of claim 1, wherein slew rate of said current is limited to 200A (max) per sec.
12. The degaussing unit of claim 1, wherein said degaussing unit incorporates built in test features to check status of one or a combination of power supply, Ethernet link, and temperature.
13. The degaussing unit of claim 12, wherein said status is communicated to said system controller over Ethernet.
14. The degaussing unit of claim 12, wherein said degaussing unit further incorporates one or more LED indicators to indicate status in respect of one or a combination of power, Ethernet and temperature.
15. The degaussing unit of claim 1, wherein said degaussing unit further comprises one or a combination of components and ICs with extended temperature ranges, customized heat sinks, amorphous core in inductor, and wherein said degaussing unit functions reliably within a temperature range of 0o to 70o C without forced cooling.
16. The degaussing unit of claim 1, wherein said degaussing unit uses MIL grade DC-DC converters.
17. The degaussing unit of claim 1, wherein said degaussing unit further comprises one or a combination of an EMI filter with feed through capacitors in the input, an inbuilt soft start, snubber circuits, ferrite cores on cable entries, internal grounding to all switching devices, galvanicaly isolated power supplies for all switching devices, switching in return path for additional filtering by inductive load, and wherein said degaussing unit is MIL-STD 461E compliant.
,TagSPECI:TECHNICAL FIELD
[0001] The present disclosure generally relates to the field of degaussing. In particular it pertains to an apparatus that delivers a programmable bipolar constant current to a degaussing coil.
BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Sea going vessels such as boats, ships and submarines are made of steel and therefore tend to get magnetized under influence of earth’s magnetic field. This typically happens during exposure to earth’s magnetic field in the same direction for relatively long time such as during their stay at shipyards or travelling long distances in the same direction which are not uncommon.
[0004] While such magnetization of ships or other sea going vessels (use of term ship shall cover all such vessels hereinafter) may be harmless for many of them, it can pose a serious hazard to those which are target of enemy attacks. This is so because various weapons used to attack ships, such as magnetic fuse mines, torpedoes, etc. detect magnetic signature of ships to target them. In view of this and to ensure their safety, ships are usually subjected to degaussing.
[0005] Degaussing is the process of decreasing or eliminating a remnant magnetic field and was originally applied to reduce ships' magnetic signatures during WWII. Besides ships, degaussing units are also used to reduce magnetic fields in CRT monitors and to destroy data held on magnetic data storage.
[0006] Due to magnetic hysteresis it is generally not possible to totally eliminate magnetic field, therefore degaussing typically induces a very small "known" field referred to as bias. The original method of degaussing was to install electromagnetic coils into the ships, known simply as coiling. In addition to being able to bias the ship continually, coiling also allowed the bias field to be reversed in the southern hemisphere, where the mines were set to detect "S-pole down" fields.
[0007] With time, capabilities of magnetic fuses have greatly improved wherein fuses functioned by detecting not the field itself, but changes in it. This meant a degaussed ship with a magnetic "hot spot" would still set off the mine. Additionally, the precise orientation of the field is also measured; something a simple bias field cannot remove, at least for all points on the ship. To overcome these challenges, a series of ever-increasingly complex coils were introduced to offset these effects, with modern systems including no fewer than three separate sets of coils to reduce the field in all axes for each region of hull of the ship.
[0008] Since distribution of hull magnetic field is quite complex, process of hull magnetic field testing, degaussing and debugging takes considerable human, financial and material resources. Degaussing coil pertaining to each region needs to be attended to adjust magnetic field generated by changing the direction of current and/or changing ampere-turns of the coil depending on need of bias.
[0009] With advances in electronics, solid state devices and communication, it is possible to overcome these challenges by providing an apparatus that delivers a programmable bipolar constant current to a degaussing coil.
[0010] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
[0011] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
[0012] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0013] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0014] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.
OBJECTS OF THE INVENTION
[0015] An object of the present disclosure is to provide an apparatus that delivers a programmable bipolar constant current for a degaussing coil.
[0016] Another object of the present disclosure is to provide a degaussing unit that has dual Ethernet connectivity, one for remote connectivity with system controller and other for local control and debugging.
[0017] Another object of the present disclosure is to provide a degaussing unit that has natural convection and radiation cooling.
[0018] Another object of the present disclosure is to provide a degaussing unit that has built in test features for checking health status of the degaussing unit.
[0019] Another object of the disclosure is to provide a degaussing unit that communicates health status to system controller.
[0020] Yet another object is to provide a degaussing unit that has protection features such as overload shutdown, over temperature shutdown etc.
[0021] Yet another object is to provide a degaussing unit that indicates faults locally and to system controller.
[0022] Yet another object is to provide a degaussing unit that is EMI EMC (MIL-STD 461E) compliant.
SUMMARY
[0023] Aspects of present disclosure relate to an apparatus (interchangeably referred to as degaussing unit hereinafter) to deliver a programmable bipolar constant current for a degaussing coil. In an aspect power source for the apparatus can be 68Vdc to 110Vdc remote transformer rectifier unit (TRU) and its output can be a programmable bipolar constant current in range of ±30.5A to meet the requirement of a degaussing coil with resistance in the range of 0.5Ω to1.75Ω and inductance in the range of 5 to 100 mH. In another aspect, the present disclosure relates to a subsurface objects dynamic magnetism compensation unit that delivers a programmable bipolar constant current for a degaussing coil.
[0024] In another aspect of the present disclosure, the degaussing unit has an industry standard 10/100 Mbps dual Ethernet connectivity. One Ethernet is used for remote connectivity with a system controller and the other Ethernet is used for local control and debugging. In an aspect the degaussing unit is recognized by the system controller using a 6 bit IP address. The IP address is set automatically by the degaussing unit after reading the connections of the pins in the Ethernet connector.
[0025] In an aspect the disclosed degaussing unit receives exact current reference required for degaussing of the ship from the system controller which calculates the same based on various inputs viz. location on earth of the ship, heading, roll, pitch etc. In an aspect the disclosed degaussing unit is capable of receiving and accepting up to 10 updates in respect of current demand in a second. In another aspect the output current is limited within a range of -30.5 A to +30.5A irrespective of the current demanded by the system controller and load impedance.
[0026] In an aspect the second Ethernet connection of the disclosed degaussing unit is used for connectivity to a localized computing device such as but not limited to a computer or laptop that is used for debugging. The localized computing device connected to the second Ethernet connection can also be used to operate the degaussing unit in local mode in which the unit accepts input of current reference and direction from the local computing device.
[0027] In another aspect, the disclosed degaussing unit incorporates a digital signal processor (DSP) which is programmed to decide the duty cycle of the gate pulses that drive various MOSFETs to control the output current and its direction. It takes feedback of current and voltage from load and compares it with input from system controller. Based on the comparison it calculates the error value and adjusts the duty cycle of gate pulses to achieve the desired current and its direction. Further the disclosed degaussing unit also incorporates means to generate isolated gate pulses of requisite duty cycle so as to drive various MOSFETs to achieve desired output current value and direction. In another aspect use of DSP processor for controlling hardware provides fast response time i.e. near analog response time.
[0028] In an aspect the disclosed degaussing unit achieves variable DC output by chopping the 68VDC to 110VDC DC input supply. The input DC supply is chopped with switching MOSFETs by varying the duty cycles of the switching MOSFETs. In another aspect when the required duty cycle falls below a threshold value a low voltage switching is enabled for higher resolution on output. For this reason the switching MOSFETs are divided in two categories - 110VDC switching MOSFETs (high voltage switching hereinafter) and 24VDC switching MOSFET (low voltage switching hereinafter). The high voltage switching MOSFETs are used when the output current requirement is above a defined threshold such as +30.5A to +2A or -30.5A to -2A. Low voltage switching MOSFET is used for output current output below the defined threshold such as (-2A to +2A). For full (110VDC) input voltage and low current output, duty cycle required is too small to be able to achieve a high output resolution. Therefore selecting 24VDC as a supply input allows higher resolution in the PWM duty cycle and also in output current for lower output. In another aspect two High voltage MOSFETs are provided for switching in a staggering manner that ensures reduced switching losses and lower heat generation.
[0029] In another aspect the disclosed degaussing unit changes direction of current across the degaussing coil/ load by employing four MOSFETs connected in an ‘H’ bridge configuration. Change in direction of current is achieved by switching ON and OFF a pair of MOSFETs. A LC filter is also placed close to ‘H’ bridge for reducing switching noise. In another aspect current slew rate is limited to 200A (max) per sec. irrespective of the slew rate demanded by the system controller and this limit is achieved by output filter inductor. When a load transient occurs, feedback control loop senses the change in output voltage and begins to change the MOSFET duty to compensate. Even if the duty cycle is able to instantly rise to 100%, the rate at which the output current can change is limited by the value of the regulator’s output filter inductor thereby preventing any possibility of switching noise. The capacitor value is selected according to the amount of current required by the load changes as the initial current deficit must be supplied by the output capacitors until the unit can meet the load demand.
[0030] In another aspect, the disclosed degaussing unit incorporates built in test features to check status in respect of power supply, Ethernet link, temperature and other such aspects and the health status of the degaussing unit is communicated to the system controller over Ethernet or through the potential free contacts of the degaussing unit. In addition fault indications are also provided locally on the degaussing unit. In an aspect these indications are provided by LEDs and indicate status in respect of power. Ethernet, temperature etc.
[0031] In an aspect the disclosed degaussing unit is equipped with features that facilitate its reliable and consistent functioning within a temperature range 0o to 70o C. it incorporates components and ICs with extended temperature ranges, heat sink arrangement on both sides of unit for removal of trapped heat, amorphous core in inductor to prevent temperature rise in inductor even on high frequency switching. Further, use of MIL grade DC-DC converters instead of linear power supply reduces power loss and in turn keeps temperature low. Also parallel MOSFET switching in staggered mode is employed for low switching losses. In another aspect no forced cooling arrangement is provided and cooling is ensured by natural convection and radiation system using customized heat sinks. Over temperature fault detection and protection are also provided to provide protection from any untoward increase in temperature.
[0032] In another aspect the disclosed degaussing unit is EMI/EMC compliant. Due to continuous switching and dynamic load conditions input experiences discontinuous currents that are a source for conducted and radiated noise. An EMI filter with feed through capacitors in the input is used to reduce conducted noise and thus the radiated noise. Other features that lead to EMI/EMC compliance are: Inbuilt soft start, use of snubber circuits and MOSFETs having very low resistance in linear region [Rds(ON)] for reduction of switching losses, use of ferrite cores on cable entries, internal grounding to all switching devices, galvanicaly isolated power supplies for all switching devices, switching in return path for additional filtering by inductive load, firing of switching MOSFETs in staggering manner for higher overall switching frequency while simultaneously keeping frequency low for individual switching.
[0033] In another aspect the disclosed degaussing unit is compact in size and light weight to be suitable for surface/under water vessels. Its dimensions can be as small as 366mm x 240mm x 165mm. further it is possible to use more than one unit in parallel to meet higher power requirement.
[0034] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0036] FIG. 1 illustrates an exemplary representation of functional units of the degaussing unit in accordance with embodiments of the present disclosure.
[0037] FIG. 2 illustrates an exemplary representation of architecture of the degaussing unit indicating major computation blocks in accordance with embodiments of the present disclosure.
[0038] FIG. 3(a) and FIG. 3(b) illustrate exemplary circuit diagram of four bridge MOSFETs with forward direction current across load and reverse direction current across load respectively in accordance with embodiments of the present disclosure.
[0039] FIG. 4 illustrates an exemplary image of main control card of the degaussing unit in accordance with embodiments of the present disclosure.
[0040] FIG. 5 illustrates an exemplary image of driver card of the degaussing unit in accordance with embodiments of the present disclosure.
[0041] FIG. 6 illustrates an exemplary image of power supply card of the degaussing unit in accordance with embodiments of the present disclosure.
[0042] FIG. 7 illustrates an exemplary image of switching card of the degaussing unit in accordance with embodiments of the present disclosure.
[0043] FIG. 8 illustrates an exemplary image of bridge card of the degaussing unit in accordance with embodiments of the present disclosure.
[0044] FIG. 9 illustrates an exemplary schematic diagram indicating configuration of MOSFETs and respective heat sinks on housing of the degaussing unit in accordance with embodiments of the present disclosure.
[0045] FIG. 10 illustrates an exemplary schematic diagram indicating configuration of various cards and input capacitor in the housing of the degaussing unit in accordance with embodiments of the present disclosure.
[0046] FIG. 11 illustrates an exemplary image indicating configuration of various cards and other items in the housing of the degaussing unit in accordance with embodiments of the present disclosure.
[0047] FIG. 12 illustrates an exemplary schematic diagram of final assembly of degaussing unit in accordance with embodiments of the present disclosure.
DETAILED DESCRIPTION
[0048] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0049] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0050] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0051] Embodiments of present disclosure pertain to a degaussing unit that can deliver a programmable bipolar constant current for a degaussing coil. In an embodiment the disclosed degaussing unit can receive exact current reference required for degaussing of the ship from a remote system controller through Ethernet and is capable of receiving and accepting up to 10 updates in respect of current demand in a second. In another aspect, the present disclosure relates to a subsurface objects dynamic magnetism compensation unit that delivers a programmable bipolar constant current for a degaussing coil.
[0052] In an embodiment the disclosed degaussing unit incorporates a digital signal processor (DSP) which is programmed to decide the duty cycle of the gate pulses that drive various MOSFETs to control the output current and its direction based on feedback of current and voltage from load and input from system controller. In another aspect use of DSP processor for controlling hardware provides fast response time i.e. near analog response time.
[0053] In another embodiment the disclosed degaussing unit achieves variable DC output by chopping the 68VDC to 110VDC DC input supply with switching MOSFETs by varying the duty cycles of the switching MOSFETs. In another embodiment a low voltage switching MOSFET and a set of two high voltage switching MOSFET are provided for higher resolution on output. In another embodiment two high voltage MOSFETs are switched in a staggering manner that ensures reduced switching losses and lower heat generation.
[0054] In another embodiment the disclosed degaussing unit changes direction of current across the degaussing coil/ load by switching ON and OFF four MOSFETs connected in an ‘H’ bridge configuration. In another embodiment a LC filter is placed close to ‘H’ bridge for reducing switching noise. In another aspect output filter inductor limits current slew rate to 200A (max) per sec. irrespective of the slew rate demanded by the system controller. In another aspect the capacitor value is selected according to the amount of current required by the load changes as the initial current deficit must be supplied by the output capacitors until the unit can meet the load demand.
[0055] In another embodiment the disclosed degaussing incorporates components and ICs with extended temperature ranges, heat sink arrangement on both sides of unit for removal of trapped heat, amorphous core in inductor to prevent temperature rise in inductor even on high frequency switching. Further, uses of MIL grade DC-DC converters instead of linear power supply reduces power loss and in turn keeps temperature low. Also parallel MOSFET switching in staggered mode is employed for low switching losses. In another aspect no forced cooling arrangement is provided and cooling provided by natural convection and radiation system using customized heat sinks is enough to facilitate its reliable and consistent functioning within a temperature range 0o to 70o C. Over temperature fault detection and protection are also provided to provide protection from any untoward increase in temperature.
[0056] In another embodiment the disclosed degaussing unit incorporates an EMI filter with feed through capacitors in the input, soft start to limit the in-rush current, snubber circuits and MOSFETs having very low resistance in linear resign for reduction of switching losses, ferrite cores on cable entries, internal grounding to all switching devices, galvanicaly isolated power supplies for all switching devices, switching in return path for additional filtering by inductive load, firing of switching MOSFETs in staggering manner to make it EMI/EMC compliant.
[0057] Various embodiments and features shall now be described in detail with reference to drawings.
[0058] Referring to FIG. 1, the disclosed degaussing unit can be said to comprise of a number of functional modules. First of these multi-loop controller 102 which can be a digital signal processor and can receive exact current reference required for degaussing of the ship from a remote system controller which calculates the same based on various inputs viz. location on earth of the ship, heading, roll, pitch etc.
[0059] In an embodiment the degaussing unit can be connected to the remote system controller through Ethernet connection. In an embodiment of the present disclosure, the degaussing unit can have an industry standard 10/100 Mbps dual Ethernet connectivity. One Ethernet can be used for remote connectivity with the system controller and the other Ethernet can be used for local control and debugging. In an aspect the degaussing unit is recognized by the system controller using a 6 bit IP address. The IP address can be set automatically by the degaussing unit after reading the connections of the pins in the Ethernet connector.
[0060] In an embodiment the second Ethernet connection of the disclosed degaussing unit is used for connectivity to a localized computing device such as but not limited to a computer or a laptop that is used for debugging. The localized computing device connected to the second Ethernet connection can also be used to operate the degaussing unit in local mode in which the unit accepts input of current reference and direction from the local computing device.
[0061] In an embodiment the multi-loop controller 102 can take feedback of current and voltage from load and compare it with input from system controller. Based on the comparison it can calculate the error value that can be used to adjust duty cycle of gate pulses to achieve the desired current and its direction. In another aspect use of DSP processor for controlling hardware provides fast response time i.e. near analog response time.
[0062] In an embodiment, the disclosed degaussing unit is capable of receiving and accepting up to 10 updates in respect of current demand in a second. In another aspect the output current is limited within a range of 30.5 A to +30.5A irrespective of the current demanded by the system controller and load impedance.
[0063] MOSFET driver 104 can receive the calculated error values from the multi-loop controller 102 and can generate isolated gate pulses of requisite duty cycle so as to drive various MOSFETs to achieve desired output current value and direction.
[0064] As depicted in FIG. 1, the disclosed degaussing unit can receive power at 68Vdc to 110Vdc and power source can be a remote transformer rectifier unit (TRU). The received power can go through an EMI filter 106. Due to continuous switching and dynamic load conditions that are generated during the process of meeting the varying current requirements of the degaussing coil, input experiences discontinuous currents that are a source for conducted and radiated noise. In an embodiment the conducted noise and thus the radiated noise can be reduced by feed through capacitors incorporated in the EMI filter 106.
[0065] After the EMI filter 106, the received power can go through a soft start module 108. In an embodiment the soft start module 108 can work to limit in rush current and reduce noise that may emanate on account of steep changes in current.
[0066] DC-DC converter 110 that receives the power thereafter can have a number of DC-DC converters such as one number of (68V- 110VDC) to 24VDC converter, another one number of 24VDC to 5VDC converter and 6 numbers of 24VDC to 15VDC converters
[0067] In an embodiment the converted 5VDC supply can be used for power supply of multi-loop controller 102 and converted 15VDC supply can be used to generate isolated gate pulses. Converted 24VDC supply can be for low voltage switching MOSFET, details of which shall be described in subsequent paragraph. In an embodiment a separate DC-DC converter can be used for each MOSFET driver therefore 6 numbers of 24Vdc to 15Vdc converters are provided to meet the requirement of generating 6 isolated gate pulse signals. In another embodiment MIL grade DC-DC converter instead of linear power supply are used to reduce power loss and in turn keeps temperature low.
[0068] Input selector and chopper 112 is configured to achieve variable DC output by chopping the 68VDC to 110VDC DC input supply. In an embodiment the input DC supply is chopped with switching MOSFETs by varying the duty cycles of the switching MOSFETs. In an aspect duty cycle signal is provided by MOSFET driver module 104. In an embodiment when the required duty cycle falls below a threshold value a low voltage switching is enabled for higher resolution on output. For this reason the switching MOSFETs are divided in two categories - high voltage switching MOSFETs that operate at 110VDC and low voltage switching MOSFET which operate at 24VDC.
[0069] In an embodiment of application the high voltage switching MOSFETs can be used when the output current requirement is above a defined threshold. In the preferred embodiment the threshold is kept at 2 A. Therefore high voltage switching MOSFETs are used when the output current requirement is +30.5A to +2A or -30.5A to -2A. On the other hand low voltage switching MOSFET can be used when the output current requirement is below the defined threshold. Since in the preferred embodiment the threshold is kept at 2 A, low voltage switching MOSFET is used when the output current requirement is (-2A to +2A). For full (110VDC) input voltage and low current output, duty cycle required is too small to be able to achieve a high output resolution. Therefore, selecting 24VDC as a supply input allows higher resolution in the PWM duty cycle and also in output current for lower output. In another embodiment two high voltage MOSFETs are provided for switching in a staggering manner that ensures reduced switching losses and lower heat generation.
[0070] Chopped 68VDC to 110VDC DC input supply that meets the variable DC output requirement can now be fed to inverter for current reversal 118 to meet the requirement of direction of current in the degaussing coil. However as load transient occurs, the feedback control loop can sense change in output voltage and begin to change the MOSFET duty to compensate and duty cycle can instantly rise to 100%. However the rate at which the output current can change needs to be limited to keep the noise within permissible limits. Therefore a filter 116 such as LC filter can be placed close to bridge that can reduce switching noise by limiting the rate at which the output current can change. The current slew rate is limited by its output filter inductor. In an aspect output filter inductor can limit the current slew rate to 200A (max) per sec. irrespective of the slew rate demanded by the system controller. The capacitor value is selected according to the amount of current required at the time of load changes because the initial current deficit must be met by the output capacitor until the unit can meet the load demand.
[0071] In an embodiment a freewheeling diode 114 is also provided to prevent sudden voltage spikes/to filter back EMF generated by swift current reversals.
[0072] Inverter for current reversal 118 can have four MOSFETs connected in an ‘H’ bridge configuration and change in direction of current can be achieved by switching ON and OFF a pair of MOSFETs.
[0073] Output 120 from Inverter for current reversal 118 can be configured with sensor 122 to sense the output current and provide a feedback to multi-loop controller 102. The sensor 122 can be a Hall Effect current sensor. Output 120 can be fed to a degaussing coil with resistance in the range of 0.5Ω to1.75Ω and inductance in the range of 5 to 100 mH.
[0074] FIG. 2 illustrates an exemplary representation of architecture of the degaussing unit indicating major computation blocks in accordance with embodiments of the present disclosure. The current reference 202 sent by system controller can be received by current extrapolator 204 that is configured to smoothen the changes in coil current. The current reference is received from system controller at 10Hz (10 times a sec.) but the degaussing unit is configured to update the coil current at 100Hz (100 times a sec.) by extrapolating from previously received current settings in order to smoothen the changes in coil current. The extrapolation mechanism can be tolerant of time jitter in the receipt of each message. Messages received within 20ms of the targeted 100ms interval are treated as having arrived at the target time. If no message is received by 200ms after the target time by the DU, it forces the output to the last current setting received and assumes the link to the controller has failed.
[0075] Output from current extrapolator 204 can be subjected to slew rate limit and current limit by Slew Rate Limit block 206 and Current Clamp block 208 respectively. As stated earlier output current slew rate can be limited to 200A (max) per sec. in the worst case load impedance irrespective of the slew rate demanded by the system controller. The slew rate limit can be implemented in the firmware to mitigate faults.
[0076] In an embodiment of the disclosure, output current is limited by Current Clamp block 208 within -30.5 A to +30.5A irrespective of the current demanded by the system controller and load impedance. The current clamp can be implemented in the firmware to mitigate faults.
[0077] After application of respective limits by Slew Rate Limit block 206 and Current Clamp block 208, the current reference 202 can be received by Compare Block 210 that can also receive current feedback 216 from output side of the degaussing unit through Current Sensor 212 and ADC block 214. In an embodiment a Hall Effect current sensor is used to get output current feedback. The signal from Hall Effect current sensor 212 can then be fed to ADC 214 to get digital count corresponding to the output current. This count is then compared in Compare block 210 with the current reference 202 received from system controller after application of respective limits by Slew Rate Limit block 206 and Current Clamp block 208 to generate error signal 218.
[0078] The generated error signal 218 can be received by PI controller 220 that can calculate the ‘proportional’ and ‘integral’ component. The final output of the PI controller 220 can indicate voltage required to achieve the required current. The output from PI controller 220 can be received by voltage clamp block 222. In an embodiment Output voltage is limited within -52 V to +52 V irrespective of the current demanded by the system controller and load impedance and this is done by voltage clamp block 222. The voltage clamp can be implemented in the firmware to mitigate open circuit faults.
[0079] The error signal 218 after application of voltage clamp at voltage Clamp block 222 can be received by voltage to duty cycle converter block 224 that can calculate duty cycle. A reference ramp signal can be generated using a timer and a counter. The frequency of the reference ramp can determine switching frequency. The reference ramp signal can be compared with the output of the PI controller 220 to generate PWM outputs which control the switching operation of the MOSFETs in switching block 226.
[0080] The switching block 226 can comprise two categories - high voltage PMW chopper 228 that operates at 110VDC and low voltage PMW chopper 230 which operates at 24VDC. Decision to use either high voltage PMW chopper 228 or low voltage PMW chopper 230 is taken by chopper selection block 234. High voltage PMW chopper 228 can be used when the output current requirement is above a defined threshold. In the preferred embodiment the threshold is kept at 2 A. Therefore high voltage PMW chopper 228 is used when the output current requirement is +30.5A to +2A or -30.5A to -2A. On the other hand low voltage PMW chopper 230 can be used when the output current requirement is below the defined threshold. Since in the preferred embodiment the threshold is kept at 2 A, low voltage PMW chopper 228 is used when the output current requirement is (-2A to +2A). For full (110VDC) input voltage and low current output, duty cycle required is too small to be able to achieve a high output resolution. Therefore, selecting 24VDC as a supply input allows higher resolution in the PWM duty cycle and also in output current for lower output. In an embodiment high voltage PMW chopper 228 incorporates two high voltage MOSFETs for switching in a staggering manner that ensures reduced switching losses and lower heat generation.
[0081] Output of switching block 226 can be received by output inverter block 232 that is configured to reverse the direction of DC current. It can incorporate four MOSFETs arranged in H bridge configuration forming the low frequency output inverter.
[0082] FIG. 3(a) and FIG. 3(b) illustrate exemplary circuit diagram of four bridge MOSFETs with forward direction current across load and reverse direction current across load respectively in accordance with embodiments of the present disclosure. As depicted four MOSFETs A, B, C and D can be arranged in H bridge configuration. Switching A and B on while switching C and D off as depicted in FIG. 3(a) can allow current to flow in forward (left to right in the circuit) direction. Switching A and B on while switching C and D off can reverse the direction of flow from left to right as depicted in FIG. 3(b).
[0083] Thus the degaussing unit controller receives the current reference from system controller and the current reference is processed by the slew rate block 206 and is used further for calculating the error. Difference between, current reference - after the “slew rate block”- and current feedback is the current error. The current error is processed by PI controller 220 to calculate output voltage which in turns decides duty cycle of PWM. The PWM triggering pulses are applied to the appropriate switching MOSFET i.e. either high voltage PMW chopper 228 that operates at 110VDC or low voltage PMW chopper 230 which operates at 24VDC depending on the selected input DC voltage source. Direction of current flowing through the coil is decided by polarity of current reference and inverter block 232. Direction of current decides the pair of MOSFETs to be ON/OFF in low frequency Inverter circuit.
[0084] In an embodiment of application various functional modules/blocks described in preceding paragraphs can be implemented on modular cards for ease of manufacture, assembly and maintenance. There can be five cards such as main control card (MCC), driver card (DC), power supply card (PS), switching card (SWC) and bridge card (BC).
[0085] FIG. 4 illustrates an exemplary image of main control card 400 of the degaussing unit in accordance with embodiments of the present disclosure. Main control card 400 (interchangeably referred as MCC hereinafter) forms the brain of the system. MCC 400 incorporates a DSP controller 402 which is programmed such that it decides the duty cycle of the gate pulses and direction of the current based on the input from system controller and output current feedback. It takes feedback of current and voltage from load and compares it with input from system controller. Based on the comparison it calculates the error value and adjusts the duty cycle of gate pulses. Also depicted in FIG. 4 are connectors 404 for receiving 24V power supply, DC-DC converters 406 for converting received 24V supply to 5V on which the MCC 400 functions, feedback connectors 408 from current sensor at output and PMW output 410. The MCC 400 also incorporates Ethernet card connectors 412 and connectors for IP address setting 414. In addition there can be fault indication relays 416.
[0086] In an embodiment the MCC 400 configured as described above, can provide gate pulses to soft start, switching and bridge MOSFETs based on current reference from system controller, give LED indication at door of the degaussing unit for Power ON, Ethernet link, Standby, Positive/negative current and fault. In addition MCC 400 can provide protection from followings open circuit, short circuit, over current, over voltage. It can also give two port Ethernet interface for communication with system controller/local computer, provide remote mode and local mode operation wherein in remote mode the unit accepts input of current reference and direction from system controller and in local mode the unit accepts input of current reference and direction from a local computing device.
[0087] FIG. 5 illustrates an exemplary image of driver card 500 of the degaussing unit in accordance with embodiments of the present disclosure. The driver card (referred interchangeably as DC hereinafter) 500 can be configured to provide isolated gate pulses to switching card and bridge card. The DC 500 can incorporate plurality of isolated MOSFET drivers 502 to drive various MOSFETs employed by the degaussing unit. For example there can be 8 drivers. Also depicted in FIG. 5 are switching connection 504 for connection to 8 MOSFETs and power supply connection 506 to receive power supply.
[0088] FIG. 6 illustrates an exemplary image of power supply card 600 of the degaussing unit in accordance with embodiments of the present disclosure. This card is a daughter card of driver card 500 as it is configured to supply power to isolated MOSFET drivers 502. The supply card 600 can have a number of DC-DC converters such as one number of (68V- 110VDC) to 24VDC converter, another one number of 24VDC to 5VDC converter and 6 numbers of 24VDC to 15VDC converters.
[0089] These converted DC supplies are used for power supply of MCC 400 and also isolated MOSFET drivers 502. FIG. 6 depicts separate DC-DC converters 602 for each MOSFET drivers 502 and a MIL grade DC-DC converter 604. In an embodiment MIL grade DC-DC converters are used instead of linear power supply to reduce power loss and in turn keep temperature low.
[0090] FIG. 7 illustrates an exemplary image of switching card 700 of the degaussing unit in accordance with embodiments of the present disclosure. The switching card 700 is configured to chop DC input from supply (68VDC to 110VDC) with switching MOSFETs to get variable DC output. Switching MOSFETs are divided in two categories - a low voltage switching MOSFET 702 and a set of two high voltage switching MOSFETs 704 - for higher resolution on output. In another embodiment the two high voltage MOSFETs are switched in a staggering manner that ensures reduced switching losses and lower heat generation. The switching card 700 also incorporates soft start MOSFET 706 and freewheeling diode 708 in accordance with embodiments explained earlier. FIG. 7 also depicts switching input 710, high voltage switching output 712, low voltage switching output 714 and MOSFET driver connection 716.
[0091] FIG. 8 illustrates an exemplary image of bridge card 800 of the degaussing unit in accordance with embodiments of the present disclosure. The bridge card 800 can be configured to control the direction of current across the degaussing coil/ load. The bridge card 800 can have 4 MOSFETs 802-1 and 801-2 (collectively referred to as 802) connected in a ‘H’ bridge configuration. Change in direction of current can be achieved by switching ON and OFF pair of MOSFETs that is 802-1 and 802-2. The bridge card 800 can also have a LC filter placed close to bridge for reducing switching noise. filter inductor 804 of the LC filter can be configured to limit current slew rate. The capacitor value can be selected according to the amount of current required by the load changes as the initial current deficit must be supplied by the output capacitors until the unit can meet the load demand. FIG. 8 also depicts connection for capacitor 806, connector for gate pulses 808, power input 810 to the bridge card 800 and output 812 to load.
[0092] In an embodiment, all the above described cards and other items are configured within a housing so as to make total assembly compliant to governing environmental and other requirements such as IP 56 and JSS55555. The housing can incorporate customized heat sinks for improved heat management within unit. The housing can be compact in size such as 366mm x 240mm x 165mm to be suitable for surface and subsurface sea going vessels. Fron of the housing can incorporate various displays in respect of faults/status.
[0093] FIG. 9 illustrates an exemplary schematic diagram 900 indicating configuration of MOSFETs and respective heat sinks on housing of the degaussing unit in accordance with embodiments of the present disclosure. The degaussing unit can have a rectangular shaped enclosure 902 and bridge card MOSFERTs 904 and switching card MOSFETs 906 can be configured on two side walls of the enclosure 902. Respective heat sinks 908 and 910 can be configured on outside of the respective side walls so as to be effective in removing the heat dissipated by the MOSFETs. There can be openings 912 for entry of cables at bottom of the enclosure through marine grade water tight connectors.
[0094] FIG. 10 illustrates an exemplary schematic diagram 1000 indicating configuration of various cards and input capacitor in the housing of the degaussing unit in accordance with embodiments of the present disclosure. Depicted therein are switching card 700, drive card 500, power supply card 600 and input capacitor 1002 configured therein in their respective positions.
[0095] FIG. 11 illustrates an exemplary image 1100 indicating configuration of various cards and other items in the housing of the degaussing unit in accordance with embodiments of the present disclosure. Depicted therein are switching card 700, driver card 500, bridge card 800 and other related parts.
[0096] FIG. 12 illustrates an exemplary schematic diagram 1200 of final assembly of degaussing unit in accordance with embodiments of the present disclosure. Depicted therein is a front cover 1202 fixed on front opening of the enclosure 902. The front cover 1202 can incorporate ON/OFF switch 1204 and plurality of LED indicators 1206 that can be configured to display various faults and/or operating status of the degaussing unit.
[0097] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.
ADVANTAGES OF THE INVENTION
[0098] The present disclosure provides an apparatus that delivers a programmable bipolar constant current for a degaussing coil.
[0099] The present disclosure provides a degaussing unit that has dual Ethernet connectivity, one for remote connectivity with system controller and other for local control and debugging.
[00100] The present disclosure provides a degaussing unit that has natural convection and radiation cooling.
[00101] The present disclosure provides a degaussing unit that has built in test features for checking health status of the degaussing unit.
[00102] The present disclosure provides a degaussing unit that communicates health status to system controller.
[00103] The present disclosure provides a degaussing unit that has protection features such as overload shutdown, over temperature shutdown etc.
[00104] The present disclosure provides a degaussing unit that indicates faults locally and to system controller.
[00105] The present disclosure provides a degaussing unit that is EMI EMC compliant.