Claims:1. A mixed-core transformer comprising:
an inner core having a first core score, the first core score being associated with magnetic characteristics, core loss, and thermal characteristics of inner core;
an outer core configured outside the inner core such that the outer core covers at least a portion of the inner core, the outer core being associated with magnetic characteristics, core loss, and thermal characteristics of the outer core, the second core score being less than the first core score ; and
a primary winding and a secondary winding, configured with each of the inner and the outer cores.
2. The mixed-core transformer as claimed in claim 1, wherein the thermal characteristics pertain to any or a combination of temperature and thermal conductivity.
3. The mixed-core transformer as claimed in claim 1, wherein the magnetic characteristics pertain to any or a combination of core loss, temperature, and relative permeability.
4. The mixed-core transformer as claimed in claim 1, wherein the U-U cores could be replaced by an inner core having I-shaped structure, and wherein the outer core has C-shaped or C shaped structure of suitable dimension.
5. The mixed-core transformer as claimed in claim 1, wherein each of the first and second core scores increase with an increase in thermal conductivity of the inner core and the outer core, respectively.
6. The mixed-core transformer as claimed in claim 1, wherein the inner core is made of nanocrystalline materials.
7. The mixed-core transformer as claimed in claim 1, wherein each of the primary winding and the secondary winding is arranged with the inner and the outer core in a one layer, and wherein the primary winding and the secondary winding are thermally decoupled.
8. An induction heating system comprising:
a control circuitry configured according to zero voltage zero current switching (ZVZCS) inverter topology, the control circuitry comprising:
a multi-core transformer comprising:
an inner core having a first core score, the first core score being associated with magnetic characteristics, core loss, and thermal characteristics of inner core,
an outer core configured outside the inner core such that the outer core covers at least a portion of the inner core, the outer core being associated with magnetic characteristics, core loss, and thermal characteristics of the outer core, the second core score being less than the first core score, and
a primary winding and a secondary winding, configured with each of the inner and the outer cores.
9. The induction heating system as claimed in claim 1, wherein the inner core and the outer core form a toroidal core.
, Description:FIELD OF INVENTION
[001] The present disclosure relates to transformers in induction heating system, and more particularly, to transformers with mixed core configuration to allow effective utilization of core configuration to avoid creation of hot spots, thereby achieving the maximum power delivery. 5
BACKGROUND OF THE INVENTION
[002] 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 10 invention, or that any publication specifically or implicitly referenced is prior art.
[003] Several power converter topologies exist for induction heating systems. The selection of a topology depends on several aspects such as power and frequency, quantum of power to be delivered, and even legacy of manufacturing process etc. In typical power controllers used for feeding series tank circuit, the 15 power transferred to metallic object such as welding joint is indirect and the coil current is large. Hence, a transformer is essentially needed to reduce current stress in its primary side. Further, configuration of tank circuit, power converter topology and the transformer together play inclusive roles to optimize the whole system. 20
[004] As known in the art, transformer is a typical part of induction heating systems used for pre and post weld treatment of welding structures. The induction heating systems used in heat treatment for welding joints employ mostly air-cooled coils which may be extremely flexible to meet functional requirement of different structures and joints whose physical dimensions may vary greatly. The 25 air cooled coils are suitable for these moderate power density (W/cm2) applications. However, in post weld heat treatment applications, water cooled coils are preferred due to large soaking time (>10 hrs) at high temperature (>750 deg C) and high temperature around coil. Even there the transformer is air-cooled. Air cooled transformers are more energy efficient. 30
3
[005] The optimization of transformer is critical for induction heating system. Its basic elements are the primary and secondary windings, the magnetic circuit consisting of suitable soft magnetic materials, the insulation between windings as well as between different layers. Ideally, the power loss in the transformer should be negligible. 5
[006] Over the years, several design approaches have emerged to achieve energy efficient transformer. Power loss takes place in core and copper. Core loss, primarily depends on properties of magnetic material. For copper loss, in particular, proximity effects caused by leakage fluxplay significant role.
[007] Therefore, there is a need to achieve highly efficient transformer, which 10 overcomes above-mentioned and other limitations of existing approaches.
[008] 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 15 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.
OBJECTIVE OF THE INVETION
[009] Some of the objects of the present disclosure, which at least one 20 embodiment herein satisfies are as listed herein below.
[0010] A general object of the present disclosure is to provide a transformer with mixed core configuration to allow effective utilization of core configuration to achieve the maximum power delivery.
[0011] It is an object of the present disclosure to provide a transformer with an 25 inner set of cores and outer set of cores, wherein the inner cores having superior core loss and thermal characteristics compared to the outer core.
[0012] It is an object of the present disclosure to minimize power loss i.e. both copper and core loss in the transformer.
[0013] It is an object of the present disclosure to maximize turns ratio of a 30 transformer using zero voltage zero current switched (ZVZCS) inverter topology.
4
[0014] It is an object of the present disclosure to select core material for inner cores of a transformer magnetically compatible with the core material for the outer cores.
[0015] It is an object of the present disclosure to provide the transformer with minimum length per turn and minimum number of turns to achieve optimal power 5 density.
[0016] It is an object of the present disclosure to provide a transformer which avoids formation of hot spot in cores as well as in windings by ensuring superior temperature distribution on core and copper.
[0017] Various objects, features, aspects and advantages of the present disclosure 10 will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like features.
SUMMARY 15
[0018] The present disclosure relates to transformers in induction heating system, and more particularly, to transformers with mixed core configuration to allow effective utilization of core configuration, thereby achieving the maximum power delivery.
[0019] An aspect of the present disclosure pertains to a mixed-core transformer 20 comprising: an inner set of cores having a particular value of suitability parameter core score (SCore), being associated with magnetic characteristics, core loss and thermal characteristics of inner cores; an outer core configured outside the inner cores on either side such that the outer core covers at least a portion of the inner cores, the outer core being associated with magnetic characteristics, thermal 25 characteristics, and core loss of the outer cores, the value of core score for outer cores being less than that of the inner core; and a primary winding and a secondary winding, configured with each of the inner and the outer cores.
[0020] In an embodiment, the thermal characteristics pertain to any or a combination of temperature and thermal conductivity. 30
5
[0021] In an embodiment, the magnetic characteristics pertain to any or a combination of core loss, saturation flux density, temperature, and relative permeability.
[0022] In an embodiment, the inner core and the outer core form a toroidal core.
[0023] In an embodiment, for ZVZCS inverter, both inner and outer cores have 5 toroidal structure.
[0024] In an embodiment, each of the first and second core scores increase with an increase in thermal conductivity of the inner core and the outer core, respectively.
[0025] In an embodiment, the inner core is made of nanocrystalline materials. 10
[0026] In an embodiment, each of the primary winding and the secondary winding is arranged with the inner and the outer core in a one layer, and wherein the primary winding and the secondary winding are thermally decoupled.
[0027] Another aspect of the present disclosure pertains to an induction heating controller comprising: a control circuitry configured according to zero voltage 15 zero current switching (ZVZCS) inverter topology, the control circuitry comprising: a multi-core transformer comprising: inner cores having a first core score, being associated with magnetic characteristics, thermal characteristics, and core loss of inner cores, an outer core configured outside the inner core such that the outer core covers at least a portion of the inner core, the outer core being 20 associated with magnetic characteristics, thermal characteristics, and core loss of the outer core, the core score of outer core being less than that of inner core, and a primary winding and a secondary winding, configured with each of the inner and the outer cores.
[0028] Various objects, features, aspects and advantages of the inventive subject 25 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.
[0029] Within the scope of this application it is expressly envisaged that the various aspects, embodiments, examples and alternatives set out in the preceding 30 paragraphs, in the claims and/or in the following description and drawings, and in
6
particular the individual features thereof, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments unless such features are incompatible.
BRIEF DESCRIPTION OF DRAWINGS 5
[0030] 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 10 thus is not a limitation of the present disclosure.
[0031] FIGs. 1A-1F illustrate section views of core of the proposed transformer, in accordance with embodiments of the present disclosure.
[0032] FIGs. 2A- 2E illustrate various section views of a configuration of the core with a primary and secondary winding in the transformer, in accordance with 15 embodiments of the present disclosure.
[0033] FIG. 3 illustrates a schematic diagram of the induction heating system employed with the proposed transformer, in accordance with embodiments of the present disclosure.
[0034] FIG. 4 illustrates an exemplary representation of control circuitry in the 20 induction heating system according to the zero voltage zero current switching (ZVZCS) inverter topology, in accordance with embodiments of the present disclosure.
[0035] FIGs. 5A and 5B illustrate exemplary representations of a conventional transformer and proposed transformer, respectively, in accordance with 25 embodiments of the present disclosure.
[0036] FIGs. 6A and 6B illustrate exemplary representation of voltages across search coil in each of inner core (Vsrc-A) and outer core (Vsrc-B) when secondary is open and under full load, respectively, in accordance with embodiments of the present disclosure. 30
7
[0037] FIGs. 7A and 7B illustrate exemplary graphs showing magnetizing current and voltage at primary side for the conventional transformer and the proposed transformer, respectively, in accordance with embodiments of the present disclosure.
[0038] FIGs. 8A and 8B illustrate exemplary graphs showing chopper voltage, 5 primary voltage of transformer, current in the coil, primary current in the transformer under no load for the conventional transformer and the proposed transformer, respectively, in accordance with embodiments of the present disclosure.
[0039] FIGs. 9A and 9B illustrate exemplary graphs showing primary voltage of 10 transformer and primary current in the transformer under full load for conventional transformer and proposed transformer, respectively, in accordance with embodiments of the present disclosure.
[0040] FIGs. 10A and 10B illustrate exemplary representations showing thermal characteristics of the conventional and proposed transformers under full load 15 conditions, respectively, in accordance with embodiments of the present disclosure.
DETAILED DESCRIPTION
[0041] The following is a detailed description of embodiments of the disclosure 20 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. 25
[0042] If the specification states a component or feature “may”, “can”, “could”, or “might” be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.
[0043] Exemplary embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments 30 are shown. This disclosure may however, be embodied in many different forms
8
and should not be construed as limited to the embodiments set forth herein. These embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the disclosure to those of ordinary skill in the art. Moreover, all statements herein reciting embodiments of the disclosure, as well as specific examples thereof, are intended to encompass both structural and 5 functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure).
[0044] Various terms as used herein are shown below. To the extent a term used 10 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.
[0045] The present disclosure relates to transformers in induction heating system, and more particularly, to transformers with mixed core configuration to allow 15 effective utilization of core configuration, copper windings, achieving the maximum power delivery.
[0046] Embodiments explained herein relate to transformers with mixed core configuration to allow effective utilization of core configuration, thereby achieving the maximum power delivery. The transformer generally suffers from 20 two major losses- core loss and copper loss.
[0047] Conventionally, when the inner core and the outer core having same specifications, the core does not get effectively utilized. The thermal conduction characteristics of inner cores are different than that of outer cores leading to differential temperature rise. The chance of hot spots is more on inner cores and 25 associated segments of copper windings. To decrease the core loss, the proposed transformer is provided with different core materials at inner core and outer core. The core materials at inner core and outer core is based on core score (SCore) that is defined based on corresponding core loss, magnetic and thermal characteristics of the core materials. The materials for inner core and the outer core may be selected 30 such that core score of outer core is less than that of inner cores. By configuring
9
such arrangement taking into account magnetic characteristics, thermal characteristics, and core loss, the core is utilized effectively allowing the core to reach their operating limit - magnetically, thereby increasing the efficiency of the transformer. The proposed improved transformer is used in the induction heating systems where the control circuitry configured according to zero voltage zero 5 current switching ZVZCS topology and the transformer is part of the control circuitry. The ZVZCS inverter topology minimizes power loss in the control circuitry by eliminating switching loss in power switches and minimizes the conduction loss because there is no circulating current.
[0048] Additionally, the primary and secondary winding are arranged in a 10 particular configuration to reduce copper loss. According to the configuration, the primary and secondary winding are arranged in a single layer. The power density can be improved by keeping the current density of the transformer at minimum permissible level i.e. the operating limits of windings.
[0049] FIGs. 1A-1F illustrate section views of core of the proposed transformer, 15 in accordance with embodiments of the present disclosure. As illustrated in FIGs. 1A-1F, the proposed transformer 100 may include a core 101 having an inner core 101-1 and an outer core 101-2 covering at least a portion of the inner core 101-1. The core 101 may form hollow cylinder type structure. In an exemplary embodiment, the core may have four segments as shown in FIGs. 1A-1F. Out of 20 four segments, the middle two segments form the inner core and the segments configured at the end of the cylinder form the outer core 101-2. FIGs. 1A-1F show a toroidal core, however, it would be appreciated by a person skilled in the art that any type of core configuration such as U-U or C-C core configurations can be applicable without or with some modifications. All such core configuration are 25 within the scope of the present disclosure. In an embodiment, to obtain mixed core configuration, the convention U+U and C core configuration may be replaced U+I+U or C+I+C, respectively, where I section is considered for inner core and C or U sections are considered for the outer core. Core segments should be geometrically compatible. 30
10
[0050] FIGs.2A- 2E illustrate various section views of a configuration of the core with a primary and secondary windings in the transformer, in accordance with embodiments of the present disclosure. As illustrated in FIGs. 2A-2E, the transformer may include a primary winding 102 and a secondary winding 103, each of the primary 102 and secondary 103 windings being configured around the 5 core 101.
[0051] In an embodiment, for each of the inner core 101-1 and the outer core 101-2, a core score SCore is defined based on magnetic characteristics, thermal characteristics, and core loss of the core configuration. It is expressed as follows:
??Core=????????(????,??)??????????h 10 (1)
Pc = core loss,
T = core temperature in 0C
Kth is thermal conductivity of core
? (=1) is constant. 15
Bm = maximum operating flux density
????(????,??) = relative permeability at Bm and operating temperature, where the relative permeability is a function of the maximum flux density and temperature.
[0052] In an embodiment, the outer core 101-2 has a core score (SCore) less than the core score of the inner core 101-1. The core score is associated with thermal 20 and magnetic characteristics of the respective core. The thermal characteristics may pertain to any or a combination of temperature and thermal conductivity. The thermal conductivity is directly related to the core score, its larger value helps maintain uniform temperature within the core. Therefore, inner core 101-1 may have more thermal conductivity compared to outer cores 101-2. 25
[0053] In an embodiment, the magnetic characteristics may pertain to any or a combination of core loss, temperature, maximum flux density, relative permeability, and so on. Thus, inner core may have higher relative permeability and higher maximum flux density compared to the outer core 101-2. In core score, more weightage is given to core loss Pc. Therefore, core loss of the inner 30
11
core may be less compared to the outer core, achieve higher core score. As multiple parameters being considered in selection of materials for inner core, the equation (1) makes the process easy and efficient by consolidating all the magnetic and thermal characteristics with their proportion into a single parameter i.e. core score (see Table 1). 5
TABLE 1: PROPERTIES OF POPULAR SOFT MAGNETIC MATERIALS
Type of core
Ferrite
Amorphous
Nanocrystalline
Material grade
P Grade
2605S3A
FT-3M
Bsat (T) at 20 OC
0.49
1.4
1.23
Pc in W/kg at 0.2T, 20kHz
3.26
18.6
1.9
The value of µr @0.2T
2500
>60000
>80000
The value of µr @1.1T
-
12000
>18000
Pc in W/kg at 1.1T, 2.3kHz
-
29
2.8
Score at 0.2T, 20kHz
50
20
23000
Score at 1.1T, 2.3kHz
--
29
15000
Thermal conductivity, Kth, W/mK
3.5
10
10
[0054] To reduce Pc and indirectly Pcu as well, subsequently, there have been 10 tremendous improvement in soft magnetic materials such as amorphous and nanocrystalline with large flux saturation limit and relative permeability. In an exemplary embodiment, nanocrystalline core materials, in particular, due to their small core loss, could be employed as inner core materials at high operating flux density for high frequency applications. To reduce the copper content in a 15 transformer, nano crystalline soft magnetic materials are being preferred in medium to high frequency applications, for still higher range, ferrite cores are preferred. Considering the same value of J for both the primary as well as secondary windings, copper loss (Pcu) at primary current (ip) or current iL flowing through the coil may be written as follows: 20
??????˜2????????????????=2????????????????
12
where ? is resistivity of copper, np and ns are turns at primary and secondary windings and lp is mean length per turn. The value of J is kept at permissible level. Therefore, for minimum value of Pcu, both nplp and nslp may be at respective minimum value. Therefore, the primary and secondary winding may be arranged in one layer to minimize the copper volume as well. The primary winding and 5 secondary winding are thermally decoupled. It eases the heat conduction features from cores and windings so as to avoid differential rise in temperature in cores or in windings. This feature helps increase the limit of power delivery of transformer. Along with, if inner cores with materials having higher value of SCore compared to the outer cores are chosen then superior uniform distribution of the 10 temperature is achieved both in cores and copper. It reduces power loss of the transformer and its electrical and magnetic loading could be increased for more power delivery.
[0055] FIG. 3 illustrates a schematic diagram of the induction heating system employed with the proposed transformer, in accordance with embodiments of the 15 present disclosure. As illustrated in FIG. 3, the induction heating system may include a rectifier 301, chopper 303, inverter 305, transformer 100, a tank capacitor bank 307, and coil 309. Each of the chopper and inverter may receive control switching signals from a control node (CN). The coil 309 may include an inductance L3. In an exemplary embodiment, various parameters of the induction 20 heating system are shown in Table 2.
TABLE 2: DETAILS OF INVERTER, TANK CIRCUIT AND TRANSFORMER
Parameter
Value
Parameter
Value
Nominal Vdc (V)
560
Frequency range (kHz)
10-14
Chopper frequency, kHz
8.0
Power POUT (kW)
30
Coil L3 (µH)
27.0
Capacitor Cr (µF)
6.6
Copper area of coil, mm2
80
Resistance of Cr (O)
0.001
Geometry of air cooled coil
Flexible
Bsat of core (T)
1.2
13
CD (µF) MKP type
300
C1 (µF)
200
Dia. of litz wire strand for windings of TR1 (mm)
0.25
Copper area: primary and secondary (mm2)
Primary: 22.1
Sec.: 2X30.9
Core weight Wcore (kg)
4.93
Chopper inductance L2, mH
0.75 at 80A
Core area (cm2)
21
Rated current iL (A)
230
Turns ratio np/ns
9:3
Permeability @ 1.0 T
>20k
Measured Rpri(dc) (mO)
5.1
Measured Rsec(dc) (mO)
0.61
Loss in inner cores @10 kHz, 0.6T (W/kg)
6.1
Loss in outer cores @10 kHz, 0.6T (W/kg)
12.0
Value of SCore for inner cores at 0.6T, 10.0 kHz
660
Value of SCore for outer cores at 0.6T, 10.0 kHz
90
[0056] FIG. 4 illustrates an exemplary representation of control circuitry in the induction heating system according to the ZVZCS inverter topology, in accordance with embodiments of the present disclosure. In the induction heating system, the control circuitry is configured according to zero voltage zero current 5 switching (ZVZCS) topology, where the proposed transformer is part of the control circuitry. This topology minimizes power loss in the control circuitry by eliminating switching loss in power switches and minimizes the conduction loss because there is no circulating current. It helps maximize the turns ratio in case of toroidal cores with minimum value of np and ns. 10
[0057] FIGs.5A and 5B illustrate exemplary representations of a conventional transformer 500 and proposed transformer100, respectively, in accordance with embodiments of the present disclosure. A comparative analysis can be performed between the conventional transformer and the proposed transformer to analyze the performance of the proposed transformer compared to the conventional 15 transformer. FIG. 5A shows four coil segments of the same material, whereas FIG. 5B shows four coil segments of two different materials. In FIG. 5B, the middle two segments are of the same materials and outer two segments are of the same materials forming inner and outer cores respectively, where core score of the inner core segments is greater than the core score of the outer core segments (see 20
14
Table 2). In order to determine magnetic compatibility of one core material with another core material, search coils are employed. As shown in FIG. 5B, search coils 104 and 105 are magnetically coupled with coil segment of the inner core 101-1 and the outer core 101-2, respectively. Except the materials, the transformers shown in FIGs.5A and 5B are the same. The performances of two 5 transformers can be analyzed based on the following parameters:
1. Magnetizing current of both the transformers
2. No load performance of control circuitry using both conventional and proposed transformers
3. Full load performance of the control circuitry using both conventional and 10 proposed transformers. It includes the temperature characteristics in cores and copper winding.
[0058] FIGs. 6A and 6B illustrate exemplary representations of voltages across search coil in each of inner core and outer core under no load (secondary is open) and full load, respectively, in accordance with embodiments of the present 15 disclosure. As shown in FIGs. 6A and 6B, the voltage Vsrc-A and Vsrc-B across search coils of inner 105 and outer core 104, respectively, are the same, where Vsrc-A indicates voltage across search coil for inner coil 105 and Vsrc-B indicates voltage across search coil for outer coil 104. Therefore, materials of inner core 101-1 is magnetically compatible with the materials of outer core 101-2. 20
[0059] FIGs.7A and 7B illustrate exemplary graphs showing magnetizing current and voltage at primary side for the conventional transformer 500 and the proposed transformer 100, respectively, in accordance with embodiments of the present disclosure. FIGs. 7A and 7B show waveforms of primary voltage and current of transformer when the terminals of the secondary winding are disconnected. In 25 such cases, the primary current is the magnetizing current. The magnetizing current and primary voltage are the same for both the conventional transformer 500 and the proposed transformer 100. It indicates that they are magnetically compatible.
[0060] FIGs.8A and 8B illustrate exemplary graphs showing chopper voltage VCH, 30 primary voltage of transformer, current in the coil, primary current in the
15
transformer under no load for the conventional transformer and the proposed transformer, respectively, in accordance with embodiments of the present disclosure. In induction heating system, even under no load condition, the rated current flows through the coil and transformer. VCH differentiates the conventional transformer and the proposed transformer any difference in loss, mostly eddy 5 current loss caused by large currents in windings. The difference in value of VCH for two transformers under no load condition would indicate which set of cores were superior. The proposed transformer with mixed core configuration has lower chopper voltage VCH compared to the conventional transformer. Therefore, power loss in the proposed transformer is comparatively less under no load condition. 10
[0061] FIGs.9A and 9B illustrate exemplary graphs showing primary voltage of transformer and primary current in the transformer under full load for conventional transformer 500 and proposed transformer 100, respectively, in accordance with embodiments of the present disclosure. Both the conventional and the proposed transformers deliver rated power effectively. 15
[0062] FIGs. 10A and 10B illustrate exemplary representations showing thermal characteristics of the conventional and proposed transformers, respectively, in accordance with embodiments of the present disclosure. As described above, each of the conventional and proposed transformer may include four coil segments – two inner core segments and two outer core segments. FIGs. 10A and 10B show 20 the same arrangement of the core segments of each of the conventional and proposed transformer as shown in FIG. 5A and 5B, respectively. The temperature of the core segments may be considered as TC1, TC2, TC3, TC4 in sequence with their arrangement, where TC2 and TC3 correspond to temperatures of inner coil segments; and TC1 and TC4 correspond to temperatures of outer coil segments. 25 TP1 and TS2 are the temperatures of the primary winding and the second winding, respectively. As shown in Table 3 below, there is large variation in temperature of the coil segments for the conventional transformer, whereas, in the proposed transformer, the temperature distribution is more uniform, which clearly indicates that thermal characteristics of the proposed transformer are better 30 compared to the conventional transformer. The uniform distribution of
16
temperature allows the core to reach their magnetic flux limit before reaching their thermal limit, thereby improving the overall performance of the transformer.
Table 3: COMPARATIVE PERFORMANCE OF TWO TRANSFORMERS
Parameter
Conventional Transformer
Proposed Transformer
Average value of Vpri on load, V
450.0
449.8
Primary current of TR1, A
73
73
Value of fs when coil not loaded, kHz
12.13
12.14
Value of fs when coil loaded, kHz
13.66
13.63
Input power to TR1 (4b), W
29565
29552
Copper loss, W
65.3
65.3
Approx. core loss, W
54
41
Efficiency of transformer
99.6
99.64
Ambient temperature, 0C
34.8
34.9
Temperature readings in four cores, 0C (TC1-TC4)
TC1: 57.1; TC2: 63.0; TC3: 63.8 and TC4: 56.0
TC1: 56.7; TC2: 56.0; TC3: 56.3 and TC4: 56.9
Temp. reading in two winding inside tunnel, 0C primary winding and secondary winding
TP1: 81.1 TS1: 78.6
TP1: 78.6; TS1: 76.5
5
[0063] Thus, the present disclosure provides a transformer with different core materials stacked at inner and outer core. The core materials in the inner core and the outer core are placed based on a core score which is obtained by consolidating all the magnetic and thermal characteristics with their proportions. While determining the core score, the core loss is also taken into account. The 10 arrangement of the core materials in inner and outer cores according to their core score allows uniform temperature distribution across all the core segments of
17
inner and outer core as well as reduces the power loss. It boosts for superior use of core and copper.
[0064] It is to be appreciated that though the embodiments of the present disclosure have been explained the transformer with reference to an induction heating system, the concept of the transformer can be used for other high-5 frequency single phase power electronics applications, and all such applications are within the scope of the present application without any limitations whatsoever.
[0065] While embodiments of the present invention have been illustrated and described, it will be clear that the invention is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions, and equivalents 10 will be apparent to those skilled in the art, without departing from the spirit and scope of the invention, as described in the claim.
[0066] In the foregoing description, numerous details are set forth. It will be apparent, however, to one of ordinary skill in the art having the benefit of this disclosure, that the present disclosure can be practiced without these specific 15 details. In some instances, well-known structures and devices are shown in block diagram form, rather than in detail, to avoid obscuring the present invention.
[0067] While the foregoing describes various embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof. The disclosure is not limited to the described 20 embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the disclosure when combined with information and knowledge available to the person having ordinary skill in the art.
ADVANTAGES OF THE INVENTION 25
[0068] The present disclosure provides a transformer with mixed core configuration to allow effective utilization of core configuration to achieve the maximum power delivery.
[0069] The present disclosure provides a transformer with an inner set of cores and outer set of cores, wherein the inner core having superior power loss, 30
18
magnetic and thermal characteristics compared to outer cores. The number of cores in each set could vary.
[0070] The present disclosure minimizes power loss i.e. both copper and core loss in the transformer.
[0071] The present disclosure maximizes turns ratio of a transformer using 5 ZVZCS inverter topology. It minimizes the primary side current as well as the length of secondary conductor.
[0072] The present disclosure allows selection of core material for an inner core of a transformer magnetically compatible with the core material for the outer core.
[0073]The present disclosure provides a transformer with minimum length per 10 turn and minimum number of turns to achieve optimal power density.
[0074] The present disclosure provides a transformer which avoids formation of hot spot in core as well as in windings by ensuring superior temperature distribution on core and copper.