Claims:1. A SOSMC based multi-loop power controller comprising of:
at least two power converters, wherein inputs of these converters are adapted to be electrically coupled to an electrical power source, and output of each of the power converters are connected in parallel, and adapted to be electrically coupled to an electrical load;
at least two second-order sliding current (SOSMC) based controllers, each operatively coupled to one of the at least two power converters; and
a current reference generator circuit operatively coupled to a reference voltage, and configured between the parallelly connected output of the at least two power converters, and at least two SOSMC based current controllers,
wherein the current reference generator circuit is configured to monitor one or more electrical parameters associated with the parallelly connected output of the at least two power converters, and the connected electrical load, and correspondingly transmit a set of reference current signals to the at least two SOSMC controllers to enable controlled synchronization and sharing of current between the at least two power converters.
2. The SOSMC based multi-loop power controller as claimed in claim 1, wherein the parallelly connected output of the at least two power converters comprise of a first terminal and a second terminal, adapted to electrically couple the SOSMC based multi-loop power controller to the electrical load.
3. The SOSMC based multi-loop power controller as claimed in claim 2, wherein the electrical load is the arc in submerged arc welding (SAW) process, wherein the first terminal is electrically connected to a contact tube of the SAW apparatus, and the second terminal is electrically connected to a workpiece of the SAW apparatus.
4. The SOSMC based multi-loop power controller as claimed in claim 1, wherein each of the at least two power converters comprises of:
a 3-phase full-bridge rectifier electrically coupled to the electrical power source;
an IGBT based current controlled inverter operatively coupled to an output side of the 3-phase full-bridge rectifier and filter, and operatively coupled to a corresponding SOSMC controller; and
a transformer, wherein an output of the current controlled inverter is electrically connected to a primary side of the transformer; and
wherein a secondary side of the transformer is adapted to be electrically coupled to a secondary side of another transformer among the at least two power controllers to provide the parallelly connected output of the at least two power converters.
5. The SOSMC based multi-loop power controller as claimed in claim 4, wherein each of the at least two power converters comprises:
a filter comprising a first inductor and a capacitor, configured between the 3-phase full-bridge rectifier and the IGBT based current controlled inverter;
a set of output diodes configured on the secondary side of the transformer; and
a set of DC chokes.
6. The SOSMC based multi-loop power controller as claimed in claim 5, wherein the SOSMC based multi-loop power controller comprises two heat sinks for each of the at least two power converters and adapted to facilitate dissipation of heat generated by each of the at least two power converters.
7. The SOSMC based multi-loop power controller as claimed in claim 6, wherein one of the two heat sinks is configured with a primary side of the corresponding power converter comprising the 3-phase full-bridge rectifier, and the IGBT based current controlled inverter, and another heat sink among the two heat sinks is configured with output diodes of the corresponding power converter.
8. The SOSMC based multi-loop power controller as claimed in claim 6, wherein the SOSMC based multi-loop power controller comprises a thermal switch of predefined thermal cut-off temperature, is operatively coupled to each of the two heat sinks associated with each of the at least two power converters.
9. The SOSMC based multi-loop power controller as claimed in claim 1, wherein the at least two SOSMC controllers are configured to provide a predefined high gain, a predefined time convergence, and a predefined small settling time.
, Description:TECHNICAL FIELD
[0001] The present disclosure relates to the field of electrical engineering, and more particularly the present disclosure relates to a power controller with a second-order sliding mode current controller (SOSMC) based multi-loop parallelly connected power converters for high power applications including but not limited to submerged arc welding processes, which has simplified and improved heat removal, and controlled and synchronized current sharing among the power converters.

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] In high power arc welding applications such as for submerged arc welding process the energy in the arc created between the tip of an electrode and a base metal is used to melt both the tip of the electrode as well as the workpiece. The total heat input H (J/m) to the process at arc current Ia is expressed as,
. Here, Varc is arc voltage, ? is arc efficiency, ?e is resistivity (?/m) of electrode wire, R is the travel speed of electrode tip and ls is electrode extension.
[0004] The maximum operating arc efficiency of different arc welding processes are Gas tungsten arc welding (GTAW): 0.64, Shielded manual arc welding (SMAW): 0.85, Gas metal arc welding (GMAW): 0.95, and Submerged arc welding (SAW): 0.99. Apart from meeting superior energy efficiency criteria, the SAW process offers better utilization of the energy generated in the welding arc, the process yields better weld quality with increased productivity. As the welding arc is submerged in flux, both arc radiation and welding fumes are negligible and the process is most welder friendly. Still, due to their high initial cost and elaborate arrangement for welding, they are preferred in high current and high-power applications. Moreover, they are not suitable for all-position welding.
[0005] FIG. 1 illustrates a typical arrangement of the SAW process as well as the joint under making using the same process. In arc welding, metal joints are made using energy generated in the arc. To make a good arc welding joint the constant voltage (CV) processes mostly involve multi-input control where the feeding of electrode metal is motorized, in SAW the travel speed is as well motorized. The multiple events involved in the creation of welding joints include electric arc creation, creation of molten droplet, control of arc length, and drop detachment.
[0006] The basic element in arc welding is the electric arc. Its creation and control are important functions of the controller. At current Ia, arc voltage Varc is expressed as, . Here E (V/m) is field intensity of arc, V0 is anode and cathode drop together, and Ra is arc resistance. For controller design, basic mathematical expressions are listed below.
[0007] The arc length ha in FIG. 2 and 3 is expressed as, , The CT is a contact tube to workpiece distance, in SAW, due to motorized movement of the electrode tip, the value of CT is constant. For current control, the dynamics of arc current could be expressed as, . Here Voc is the value of secondary side rectified open-circuit voltage, Rs is the equivalent resistance of the controller reflected at the secondary side, and L1 is the inductance in secondary DC side.
[0008] The wire melting rate is expressed as, . Where md i.e., the droplet mass, c1 and c2 are melting rate constant. In SAW, for a particular application, CT is held constant, the dynamics of electrode extension ls or arc length ha could be expressed as, . Vf is the feed rate of electrode wire and ?w is the density of wire and d is the diameter of the electrode wire. The arc length is maintained constant when the melting rate and feed rate are matched. In that situation, the arc voltage is also constant.
[0009] The quality of the joint could be judged by multiple parameters. E.g., the parameter bead reinforcement G could also be used to define the weld quality. It is defined as the transverse cross-sectional area of deposited metal on the welded section, whose formula is, . With the known value of d and of wire feed speed Vf the rate of metal transfer to weld pool is known. Therefore, for quality welding joints, accurate control of Vf and R is needed. Control inputs Voc and Vf do not have any direct access to control the shape of the droplet and also for its proper transfer to the weld pool. With droplet position at x4 and droplet velocity x5 (see FIG. 2), the dynamics of the molten drop could be written as, , and . Here, Ftot is total force acting on droplet md, Bd is damping coefficient and Kd is spring constant. Though a large number of forces are active on the droplet, the surface tension force Fs and electromagnetic force Fem play dominant roles. In arcing phase, Fs helps the droplet to remain attached to the wire. For its easy transfer, its desired shape is spherical. The expression of FS is, , where ? is the surface tension coefficient of molten droplet and rw is the neck or waist radius of the molten droplet.
[0010] The expression of electromagnetic force Fem is , where f(s) is a geometric shape factor that depends on the radius of the neck and droplet. Both the travel speed R and electrode feeding speed Vf in SAW are motorized, often, for a particular welding application, their respective values are kept fixed. Therefore, for control of welding joint, current Ia is varied, it achieved through power controller by varying the value of Voc..
[0011] The characteristics of the SAW process could be diverse; it could be programmed in CV mode, CC mode and could be either AC or DC characteristics. To make a particular welding joint, the speed of wire feeding as well as the travel speed of the electrode tip are pre-decided. Therefore, the control of melting rate of electrode tip and wetting of base metal are executed through dynamic control of Voc, the current is the main control variable.
[0012] For high power applications, such as in SAW, for control of Voc, a typical phase-controlled rectifier technology as illustrated in FIG. 2 has long been in use. It involves control action at the low voltage secondary side. The size of both 50 Hz three-phase high-current transformer TX2, as well as low-frequency (300 Hz) smoothing DC choke L2 at secondary DC side, was large. The power loss in bulky high-power transformer as well as in DC choke was large. The power loss could be reduced further if operating flux density in the core and current density in copper were reduced, but the size would go up. These equipments were not mobile, though, in arc welding, they need to be place close to the joint location. For high current welding, to reduce power loss, the length of the welding cable should be minimum. Apart from bulkiness and excess power loss, due to the low frequency of operation, the control response of these controllers was poor. Genarally, major power loss took place in these passive components and comparatively a small percentage of it took place in the active components i.e., in SCRs. Power loss in passive components was distributed uniformly in core or copper, therefore, these controllers were rugged.
[0013] With further advancements, most of the drawbacks associated with phase-controlled rectifier technology have been removed through the introduction of inverter technology where the power control is shifted to the primary side of the main power transformer TX1. FIG. 3 illustrates a typical inverter technology suitable for the SAW process. Depending upon the topology used, the inverter operates at switching frequency 20 kHz onwards. Higher the switching frequency of the inverter better would be the response time and the controller would be more compact. The power density of the controller is improved, it could be easily relocated close to the joints to be made. Welding quality would be better because there is an improvement in response time of control actions, the energy in the arc is better controlled now.
[0014] The circulating current in the inverter is just the magnetizing current of transformer TX1. Therefore, the turn-off loss in IGBTs Q1-Q4 and conduction and recovery losses in antiparallel diodes D1-D4 are negligible. The conduction loss plus turn-on loss in Q1-Q4 are the major losses in this topology. However, the major part of power loss takes place in the active components. Due to complex thermal behavior, the heat removal from passive high frequency passive magnetic components is also complex. There needs to be an alternate improved approach for designing high-frequency large power arc welding controllers.
[0015] Controllers for SAW are used for applications where high productivity is demanded. The capacity rating of these controllers is large and the duty cycle, in most applications, is continuous. They need to be rugged. Though the typical inverter technology is efficient, still, significant power loss takes place, particularly, in high-frequency power components such as IGBTs, Diodes, Transformer, and DC choke. It could be difficult to remove large heat loss from these components.
[0016] However, if the thermal resistance of each component along with their respective heat spreading resistance is reduced, then thermal design gets simplified and the design of high-power equipment becomes realizable. However, because it depends on several factors (commercial reasons, etc.), nothing much could be done for bought out items such as power semiconductors. On the other hand, the thermal resistance of passive high-frequency power components is complex and depends on several factors such as core material and geometry, winding configuration, type of Litz wire, etc.
[0017] There is, therefore, a need to overcome the above drawback and provide an alternate improved approach for designing high-frequency large power arc welding controllers, which has reduced current load on the individual power converters, has robust and superior current sharing and control capability, both under steady-state as well as dynamically. Further, there is a need to improve heat removal features from each active and passive components of the controller.

OBJECTS OF THE PRESENT DISCLOSURE
[0018] Some of the objectives of the present disclosure, which at least one embodiment herein satisfies are as listed herein below.
[0019] It is an object of the present disclosure to provide an improved approach for designing high-frequency large power arc welding controllers.
[0020] It is an object of the present disclosure to implement a second order sliding mode current controller (SOSMC) in high power applications including but not limited to submerged arc welding (SAW) processes.
[0021] It is an object of the present disclosure to provide a power controller with SOSMC based multi-loop parallelly connected power converters for SAW processes.
[0022] It is an object of the present disclosure to improve current sharing in the power controller used in the SAW process.
[0023] It is an object of the present disclosure to improve spatial distribution of total power loss in power converters of the power controller used in the SAW process.
[0024] It is an object of the present disclosure to improve heat removal features from each active and passive components of the power controller.
[0025] It is an object of the present disclosure to provide robust and superior current sharing and control capability in the power controller used in the SAW process.

SUMMARY
[0026] The present disclosure relates to the field of electrical engineering, and more particularly the present disclosure relates to a power controller with a second order sliding mode current controller (SOSMC) based multi-loop parallelly connected power converters for high power applications including but not limited to submerged arc welding processes, which has simplified and improved heat removal and controlled and synchronized current sharing among the power converters.
[0027] An aspect of the present disclosure pertains to a power controller with a second order sliding mode current controller (SOSMC) based multi-loop parallelly connected power converters. The power controller may comprise of power converters being configured parallel to one another such that their outputs are parallelly connected. Further, the power converters may be electrically connected to a 3-phase electrical power source, and the parallelly connected output may be adapted to be electrically coupled to an electrical load comprising but not limited to a submerged arc welding machine.
[0028] The power controller may comprise of a supervisory voltage loop that is adapted to derive current reference based on the electrical parameters associated with the load, and may provide the same to individual power converters. The power controller may implement a robust second-order sliding-mode control function enabling circuitry to ensure superior control and sharing of current between the power converters.
[0029] In an aspect, the supervisory voltage loop may comprise of at least two second order sliding current (SOSMC) controller (collectively referred to as SOSMC current controller or SOSMC function, herein), each being operatively coupled to one of the power converters. Further, a current reference generator circuit may be operatively coupled to a reference voltage, and configured between the parallelly connected output of the power converters, and the SOSMC based current controller. The current reference generator circuit may be configured to monitor the electrical parameters associated with the parallelly connected output of the power converters and the connected electrical load. The current reference generator circuit may correspondingly transmit a set of reference current signals to the SOSMC controllers to enable controlled synchronization and sharing of current between the power converters.
[0030] In an aspect, the parallelly connected output of at least two power converters may comprise of a first terminal and a second terminal adapted to electrically couple the SOSMC based multi-loop power controller to the electrical load. In an implementation, the electrical load may be a submerged arc welding (SAW) apparatus, wherein the first terminal may be electrically connected to a contact tube of the SAW apparatus, and the second terminal may be electrically connected to a workpiece of the SAW apparatus.
[0031] In an aspect, each of the full-bridge power converters may comprise of a 3-phase full-bridge rectifier electrically coupled to the electrical power source. An insulated-gate bipolar transistor (IGBT) based current controlled inverter may be operatively coupled to an output side of the 3-phase full-bridge rectifier and may be operatively coupled with a corresponding SOSMC controller. The power converter may comprise of a transformer, wherein an output of the current controlled inverter may electrically connected to a primary side of the transformer, and a secondary side of the transformer may be adapted to be electrically coupled to a secondary side of another transformer among the parallelly configured power controllers to provide the parallelly connected output of the power converters.
[0032] In an aspect, the power controller may comprise of two heat sinks for each of the power converters, which are adapted to facilitate the dissipation of heat generated by each of the power converters. One of the two heat sinks may be configured with components belonging to the primary side of the corresponding power converter comprising of the 3-phase full-bridge rectifier, and the IGBT based current controlled inverter, and another heat sink among the two heat sinks is configured with output diodes of the corresponding power converter.

BRIEF DESCRIPTION OF DRAWINGS
[0033] 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. The diagrams are for illustration only, which thus is not a limitation of the present disclosure.
[0034] In the figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label with a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.
[0035] FIG. 1 illustrates an exemplary view of a typical arrangement of submerged arc welding process along with a magnified view of a joint under making using the same process.
[0036] FIG. 2 illustrates a schematic diagram of a typical power control arrangement for a traditional secondary side controller for the submerged arc welding process.
[0037] FIG. 3 illustrates a schematic diagram of a typical primary side power control using inverter technology for the submerged arc welding process.
[0038] FIG. 4 illustrates an exemplary circuit diagram of the proposed power controller with a second order sliding mode current controller (SOSMC) based multi-loop parallelly connected power converters, in accordance with an embodiment of the present disclosure.
[0039] FIG. 5 illustrates an exemplary control circuit for the SOSMC controller of the proposed power controller, in accordance with an embodiment of the present disclosure.
[0040] FIG. 6 illustrates an exemplary block diagram of the current reference generator of the proposed power controller, in accordance with an embodiment of the present disclosure
[0041] FIG. 7A illustrates robust current control using the SOSMC function while using 6.3mm E7018 electrode at 300A. FIG. 7B illustrates robust dynamic current control using the SOSMC function under resistive load. FIG. 7C illustrates robust dynamic current control using the SOSMC function under argon atmosphere for GTAW.
[0042] FIG. 8A illustrates a top view of the internal power and magnetic circuit of the proposed power controller, in accordance with an embodiment of the present disclosure.
[0043] FIG. 8B illustrates a rear view of a control and gate drive circuit of the proposed power controller, in accordance with an embodiment of the present disclosure.
[0044] FIGs. 9A and 9B illustrate a front view and side view, respectively, of an internal power electronics and magnetic circuit of the proposed power controller, in accordance with an embodiment of the present disclosure.
[0045] FIG. 10 illustrates an exemplary photographic view of the proposed power controller, in accordance with an embodiment of the present disclosure
[0046] FIG. 11 illustrates an exemplary photographic view of the a complete sub-merged arc welding controller that includes the proposed power controller as well as the motorised wire feeding and tip movement, in accordance with an embodiment of the present disclosure.
[0047] FIGs. 12A to 12C illustrate an exemplary view of waveforms using 2.4 mm wire for different input conditions, using the proposed power controller.
[0048] FIGs. 13A to 13C illustrate an exemplary view of waveforms using 3.15 mm wire for different input conditions, using the proposed power controller.
[0049] FIG. 14 illustrates an exemplary view of the SAW joints created on 50mm thick slab by the innovative power controller using 2.4mm and 3.15 mm electrode wire at 300A, using the proposed power controller.
[0050] FIG. 15 illustrates an exemplary view of the SAW joint created on 50mm thick slab by the innovative power controller using 3.15mm electrode wire at 800A, using the proposed power controller.

DETAILED DESCRIPTION
[0051] 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.
[0052] In the following description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present invention. It will be apparent to one skilled in the art that embodiments of the present invention may be practiced without some of these specific details.
[0053] The present disclosure relates to the field of electrical engineering, and more particularly the present disclosure relates to a power controller with a second order sliding mode current controller (SOSMC) based multi-loop parallelly connected power converters for high power applications including but not limited to submerged arc welding processes, which has improved the means of heat removal and SOSM controlled synchronized controllers achieved superior current sharing among the power converters.
[0054] According to an aspect, the present disclosure elaborates upon a proposed power controller with a second order sliding mode current controller (SOSMC) based multi-loop parallelly connected power converters. The power controller can include at least two power converters being configured parallelly to one another such that their outputs are parallelly connected. Further, the power converters can be electrically connected to a 3-phase electrical power source, and the parallelly connected output can be adapted to be electrically coupled to an electrical load including but not limited to a submerged arc welding machine. The minimally configured power controller can include at least two second-order sliding current (SOSMC) based controllers, each operatively coupled to one of the at least two power converters. Further, a current reference generator circuit can be operatively coupled to a reference voltage, and configured between the parallelly connected output of at least two power converters, and the at least two SOSMC based current controller. The current reference generator circuit can be configured to monitor one or more electrical parameters associated with the parallelly connected output of the at least two power converters, and the connected electrical load, and correspondingly transmit a set of reference current signals to the at least two SOSMC controllers to enable controlled synchronization and sharing of current between the at least two power converters.
[0055] The expression SOSMC control function u1, for, say, first controller in the control circuit domain is,

[0056] For operational simplicity and wide range control, the SOSMC control function u1 has been simplified, whose expression is for, say, first controller is,

[0057] In an embodiment, the parallelly connected output of the at least two power converters can include a first terminal and a second terminal, adapted to electrically coupled the SOSMC based multi-loop power controller to the electrical load.
[0058] In an embodiment, the electrical load can be a submerged arc welding (SAW) apparatus. The first terminal can be electrically connected to a contact tube of the SAW apparatus, and the second terminal can be electrically connected to a workpiece of the SAW apparatus.
[0059] In an embodiment, each of the at least two power converters can include a 3-phase full-bridge rectifier electrically coupled to the electrical power source; an IGBT based current controlled inverter operatively coupled to an output side of the 3-phase full-bridge rectifier, and operatively coupled to a corresponding SOSMC controller; and a transformer. The output of the current controlled inverter can be electrically connected to a primary side of the transformer, and a secondary side of the transformer can be adapted to be electrically coupled to a secondary side of another transformer among the at least two power controllers to provide the parallelly connected output of the at least two power converters.
[0060] In an embodiment, the power controller can further include a filter comprising a first inductor and a capacitor, configured between the 3-phase full-bridge rectifier and the IGBT based current controlled inverter; a set of output diodes configured on the secondary side of the transformer, and a set of DC chokes.
[0061] In an embodiment, the power controller can include two heat sinks for each of the at least two power converters and adapted to facilitate dissipation of heat generated by each of the at least two power converters.
[0062] In an embodiment, one of the two heat sinks can be configured with a primary side of the corresponding power converter comprising the 3-phase full-bridge rectifier, and the IGBT based current controlled inverter, and another heat sink among the two heat sinks can be configured with output diodes of the corresponding power converter.
[0063] In an embodiment, the power controller can include a thermal switch of predefined thermal cut-off temperature, being operatively coupled to each of the two heat sinks associated with each of the at least two power converters.
[0064] In an embodiment, at least two SOSMC controllers can be configured to provide a predefined high gain, a predefined time convergence, and a predefined small settling time.
[0065] Referring to FIG. 4, in an embodiment, the proposed power controller 400 with second order sliding mode current controller (SOSMC) based multi-loop parallelly connected power converters is disclosed. The proposed power controller 400 can include at least two power converters 402-1 to 402-N (collectively referred to as power converters 402, herein) being configured parallelly to one another such that their outputs are parallelly connected. Further, the power converters 402 can be electrically connected to a 3-phase electrical power source, and the parallelly connected output can be adapted to be electrically coupled to an electrical load including but not limited to a submerged arc welding machine.
[0066] The power controller 400 can include a supervisory voltage loop that is adapted to derive current reference based on the electrical parameters associated with the load, and can provide the same to individual power converters 402-1 and 402-N. The power controller 400 can implement a robust second-order control function enabling circuitry to ensure superior control and sharing of current between the power converters 402.
[0067] In an embodiment, the supervisory voltage loop can include at least two second order sliding current (SOSMC) controller 404-1 and, say, 404-N (collectively referred to as SOSMC current controller 404 or SOSMC function 404, herein), each being operatively coupled to one of the power converters 402-1 to 404-N. Further, a current reference generator circuit 406 can be operatively coupled to a reference voltage Vref and configured between the parallelly connected output of the power converters, and the SOSMC based current controller 404. The current reference generator circuit 406 can be configured to monitor the electrical parameters associated with the parallelly connected output of the power converters 402, and the connected electrical load. The current reference generator circuit 406 can correspondingly transmit a set of reference current signals to the synchronized SOSMC controllers 404 to enable robust and accurate sharing of current between the power converters 402-1 and 402-N.
[0068] In an embodiment, the parallelly connected output of the power converters 402 can include a first terminal (+VE) and a second terminal (-VE), adapted to electrically coupled the SOSMC based multi-loop power controller 400 to the electrical load. In an implementation, the electrical load can be a submerged arc welding (SAW) apparatus, wherein the first terminal (+VE) can be electrically connected to a contact tube of the SAW apparatus, and the second terminal (-VE) can be electrically connected to a workpiece of the SAW apparatus.
[0069] In an embodiment, each of the full-bridge power converters 402 can include a 3-phase full bridge rectifier (Rectifier 1, Rectifier-N) electrically coupled to the electrical power source. An insulated-gate bipolar transistor (IGBT) based current controlled inverter (Inverter-1, Inverter-N) can be operatively coupled to an output side of the 3-phase full bridge rectifier (Rectifier 1, Rectifier-N), and can be operatively coupled with a corresponding SOSMC controller (404-1, 404-N). The power converter 400 can include a transformer (TX31, TX3N), wherein an output of the current controlled inverter can be electrically connected to a primary side of the transformer (TX31, TX3N), and a secondary side of the transformer (TX31) of the power converter 402-1 can be adapted to be electrically coupled to a secondary side of another transformer (TX3N) of the power controller 402-N to provide the parallelly connected output of the power converters.
[0070] In an embodiment, each of the power converters 402 can further include a filter comprising a first inductor (L31, L3N), and a capacitor (C21, C2N), configured between the 3-phase full-bridge rectifier and the IGBT based current controlled inverter, to filter harmonics current to enter into the IGBT based current controlled inverter. Further, a set of output diodes is configured on the secondary side of the transformer. In an embodiment, a set of DC chokes including a second inductor (L41, L4N) can be configured with the power converter 402 on the output side to provide a smooth DC current on the output side of the power controller 400.
[0071] Referring to FIGs. 4 to 6, in an exemplary embodiment, the design, and implementation of robust 2000A using SOSMC can be validated. For 2000A, two 1000A full-bridge power converters 402-1 and 402-N can be connected in parallel. With given input conditions (Vf, R, Varc, etc.) the nominal current Inom can be pre-decided by set welding procedure and, based on feedback of Varc, the power controller delivers actual current, virtually with no error, as illustrated in FIG. 6. The current reference generator 406, based on the electrical parameter Varc and Varc-ref associated with the SAW, can update on the reference currents I1-ref and I2-ref for the two SOSMC controllers 404-1 and 404-N. Each controller, using respective robust SOSMC control function, tracks the reference signals accurately. Further, the two SOSMC controllers, say, 404-1 and 404-N can accordingly provide the PWM signals to the IGBT based inverter (Inverter-1 and Inverter-N, respectively) associated with the two power converters 402-1 and 402-N, respectively, thereby enabling controlled and synchronized sharing of 1000A current each between the two power converters 402-1 and 402-N.
[0072] In an exemplary embodiment, parameters of a single 1000A, 20KHz full-bridge power controller 402 are listed in Table 1.

TABLE-1: PARAMETERS OF EACH 1000A, 20 kHz FULL BRIDGE CONVERTER
Parameter/component Value Controller gains
VOC(max), V 72.0

?10 = 5.7 and
?11 = 5400
Maximum duty cycle, % 90.0
Turns ratio Pri:sec1:sec2: 15:2:2
Cores N87, ferrite
L1, µH 75, 1000A
Q1-Q4 FF300R12KT3
D1, D2 MMF400Y040DK1, 6 no

[0073] To study the repeatability in performance of the proposed idea several welding joints were created. Welding conditions of a few of them are listed in Table 2. A few measured output parameters are provided in FIGs. 7A to 7C. FIG. 7A illustrates robust current control using the SOSMC function while using 6.3mm E7018 electrode at 300A. FIG. 7B illustrates robust dynamic current control using the SOSMC function under resistive load. FIG. 7C illustrates robust dynamic current control using the SOSMC function under argon atmosphere for GTAW.
TABLE 2: INPUT CONDITIONS FOR INVENTION VALIDATION AND THE RESULTS
Input conditions for making SAW joints Output parameters of the controllers
d (mm) Vf (m/min) R (m/min) ls (mm) Varc-ref (V) Varc (V) Ia (A) I1 (A) I2 (A)
3.15 1.28 0.44 25 32.0 32.8 394 195 199
3.15 1.96 0.44 25 32.0 32.4 606 301 305
3.15 3.88 0.48 30 36.0 35.2 896 446 450
2.4 1.64 0.36 25 32.0 33.0 301 148 153
2.4 2.76 0.36 25 32.0 32.5 503 249 254
2.4 4.24 0.38 25 34.0 33.8 597 296 301

[0074] The reference for welding current Ia was generated in the digital domain using PIC microcontroller. Subsequently, it was equally divided and fed to the paralleled controllers. The current Ia is expressed as, , where I1 is current from the first controller and I2 is from the second one. The reference for I1 and I2 were generated by the supervisory voltage loop. The magnitude of reference was the same for both current controllers.
[0075] In an embodiment, as illustrated in FIGs. 8A to 10, the proposed power controller 400 can include two heat sinks encasing each of the power converters 402, and are adapted to facilitate dissipation of heat generated by each of the power converters 402. In an exemplary embodiment, one of the two heat sinks can be configured with a primary side of the corresponding power converter 402-1 comprising the 3-phase full bridge rectifier (Rectifier-1), and the IGBT based current controlled inverter (Inverter-1), and another heat sink among the two heat sinks can be configured with output diodes D11, D21 of the corresponding power converter 402-1. Similarly, for the second power converter 402-N, one of the two heat sinks can be configured with a primary side of the corresponding power converter 402-N comprising the 3-phase full bridge rectifier (Rectifier-N), and the IGBT based current controlled inverter (Inverter-N), and another heat sink among the two heat sinks can be configured with output diodes of the corresponding power converter 402-N.
[0076] In an exemplary embodiment, the heat sinks can be in form of a passive heat exchanger that can absorb the heat generated by the components of the power converters, and transfer the absorbed heat to a fluid medium using a coolant and pumping system, or to an ambient environment using a cooling fan, but not limited to the likes.
[0077] In an embodiment, the power controller 400 can include a thermal switch of predefined thermal cut-off temperature, being operatively coupled to each of the two heat sinks associated with each of the power converters 400. In an exemplary embodiment, a thermal switch of thermal cut-off temperature 85oC can be used, which can cut-off the power supply through the power converters if the temperature of the heat sinks exceeds 85oC.
[0078] In an embodiment, the power controller 400 can include an MCB (circuit breaker to protect the power controllers and corresponding components from fault conditions.
[0079] Referring to FIG. 5, the control circuit for the SOSMC controller 404 of the proposed power controller 400 is disclosed. SOSMC 404 is a robust control approach where, just by implementing the control algorithm, the power converters 402 can achieve zero steady-state error and finite-time convergence of control variable. It helps achieve superior dynamic performance and could be ideal for non-linear processes such as arc welding. Ideally, it does not have any wind-up. The SOSMC 404 can be configured to provide a high gain, a finite time convergence, and a small settling time.
[0080] Referring to FIGs. 12A to 12C, the waveforms represent three different welding conditions for the input conditions provided in Table-2 above, using 2.4mm electrode wire. From the wavefroms, it is clear that, in each experiment, the current sharing between the individual power converters 402-1 and 402-N was equal and the desired arc voltage was also accurately controlled. Waveforms for welding using 2.4mm wire under conditions, a) Varc-ref = 32V, Vf = 1.64m/min, R = 0.36m/min is hsown in FIG. 12A; b) Varc-ref = 32V, Vf = 2.76m/min, R = 0.36m/min is shown in FIG. 12B, and c) Varc-ref = 34V, Vf = 4.24m/min, R = 0.48m/min is shown in FIG. 12C.
[0081] Referring to FIGs. 13A to 13C, the waveforms represent three different welding conditions for the input conditions provided in Table-2 above, using 3.15mm electrode wire. From the wavefroms, it is clear that, in each experiment, the current sharing between the individual power converters 402-1 and 402-N was equal and the desired arc voltage was also accurately controlled. Waveforms for welding using 3.15mm wire under conditions, a) Varc-ref = 32V, Vf = 1.28m/min, R = 0.44m/min is shown in FIG. 13A; b) Varc-ref = 32V, Vf = 1.96m/min, R = 0.44m/min is shown in FIG. 13B, and c) Varc-ref = 36V, Vf = 3.88m/min, R = 0.48m/min is shown in FIG. 13C.
[0082] Referring to FIG. 14, in an implementation, an exemplary view of SAW joint created on 50mm thick slab by the innovative power controller using 2.4mm and 3.15 mm electrode wire at 300A, using the proposed power controller.
[0083] Referring to FIG. 15, in an implementation, an exemplary view of SAW joint created on 50mm thick slab by the innovative power controller using 3.15mm electrode wire at 800A, using the proposed power controller.
[0084] It is to be appreciated by a person skilled in the art that the robust current sharing by the power converters in the present invention has helped to increase the power rating of the equipment (power controller). Moreover, the component selection in each power controller has been eased. The total power loss of the system is now divided over a greater number of active and passive power components, including the heat spreading resistance, the overall thermal resistance will be significantly reduced.
[0085] Moreover, in interpreting the specification, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refer to at least one of something selected from the group consisting of A, B, C ….and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.
[0086] 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
[0087] The proposed invention provides an improved approach for designing high-frequency large power arc welding controllers.
[0088] The proposed invention implements a second order sliding mode current controller (SOSMC) in high power applications including but not limited to submerged arc welding (SAW) processes.
[0089] The proposed invention provides a power controller with SOSMC based multi-loop parallelly connected power converters for SAW processes.
[0090] The proposed invention improves current sharing in the power controller used in the SAW process.
[0091] The proposed invention improves the spatial distribution of total power loss in power converters of the power controller used in the SAW process.
[0092] The proposed invention improves heat removal features from each active and passive components of the power controller.
[0093] The proposed invention provides robust and superior current sharing and control capability in the power controller used in the SAW process.