Description:FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENT RULES, 2003

COMPLETE SPECIFICATION
(See Section 10 and Rule 13)

TITLE OF INVENTION:
A DC-DC CONVERTER FOR NARROW OPERATING RANGE

APPLICANT:
KALYANI POWERTRAIN LIMITED
An Indian entity having address as:
Sr. no. 49, Industry House, Opp. Kalyani Steels Limited, Mundhwa, Pune, 411036, Maharashtra, India

The following specification particularly describes the invention and the manner in which it is to be performed.
CROSS-REFERENCE TO RELATED APPLICATIONS AND PRIORITY
The present application does not claim priority from any other patent application filed in India or abroad.
TECHNICAL FIELD
The present subject matter described here, in general relates to a DC-DC converter for narrow operating range, and more specifically relates to the DC-DC converter for narrow operating range, wherein narrow operating range is obtained by achieving leakage inductance in the transformer by providing a predefined gap between a primary winding and a secondary winding of the transformer.
BACKGROUND
The subject matter discussed in the background section should not be assumed to be prior art merely because of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also correspond to implementations of the claimed technology.
An electric vehicle industry has seen upward trend in the past few years. The batteries of the electric vehicle are high voltage batteries, which provides several hundred volts of direct current (DC). However, the electric components inside the vehicle vary in their voltage requirements, with most running on a much lower voltage. This includes the radio, dashboard readouts, air conditioning, and in-built computers and displays. A DC-DC converter is a category of power converters, which converts a DC source from one voltage level to another. It can be unidirectional, (transfers power only in one direction), or bidirectional, (transfers power in both directions). Moreover, a DC-DC converter is a critical component in the architecture of the electric vehicle, wherein the DC-DC converter is configured to convert higher DC voltage from the traction of battery pack to the lower DC voltage that is needed to run vehicle accessories and recharge the auxiliary battery.
Further, the operating voltage of different electronic devices/accessories vary over a wide range, making it necessary to provide desired voltage for each device. It is well known to use buck converter and boost converter to achieve desired voltage. More specifically, the buck/step down converter provides a lower voltage than the original voltage, while the boost/step up converter supplies a higher voltage. However, an implementation of additional converters such as buck/step down converter, boost/step up converter increases the space requirement and cost, which makes designing of DC-DC converter bulky.
It is well known that leakage inductance plays a major role in DC-DC converter. Leakage inductance has the useful effect of limiting the current flows in a transformer (and load) without itself dissipating power. However, high leakage inductance affects power transfer of transformers as it increases loss and coupled inductors, as well as causing voltage spikes across DC-DC converter switches which possibly damaging them.
Therefore, there is need of the DC-DC converter which achieves the leakage inductance in the transformer without using additional components for narrow operating range.
SUMMARY
This summary is provided to introduce concepts related to a DC-DC converter for narrow operating range. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.
The DC-DC converter for narrow operating range comprises of a high voltage battery, a set of primary Metal-oxide-semiconductor field-effect transistor (MOSFETs), a transformer and a set of secondary MOSFETs. The transformer having a core with a primary winding and a secondary winding. A predefined air gap is provided in between the primary winding and the secondary winding of the core of the said transformer for achieving the leakage inductance for narrow operating range. The area of the primary windings of the transformer is greater than the area of the secondary windings.
BRIEF DESCRIPTION OF THE DRAWINGS
The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to refer like features and components.
Figure 1 illustrates a block diagram of a DC-DC converter (100) for narrow operating range, in accordance with an embodiment of the present disclosure.
Figure 2 illustrates a schematic diagram of the DC-DC converter for narrow operating range, in accordance with an embodiment of the present disclosure.
Figure 3 illustrates a switching current and voltage waveforms with a predefined air-gap between primary winding and secondary winding of a transformer, in accordance with an embodiment of the present disclosure.
Figure 4 illustrates a bobbin E70 flat link of the transformer used in the DC-DC converter for narrow operating range, in accordance with an embodiment of the present disclosure.
Figure 5 illustrates a DC-DC converter for operating with input voltage 420V and output voltage 28.8 V, in accordance with a first exemplary embodiment of the present disclosure.
Figure 6A illustrates a waveform representation of a control signal, which is applied to the set of primary MOSFETs of the DC-DC converter, in accordance with the first exemplary embodiment of the present disclosure.
Figure 6B, illustrates a waveform representation of input current, which is applied to the set of primary MOSFETs of the DC-DC converter, in accordance with the first exemplary embodiment of the present disclosure.
Figure 6C illustrates a waveform representation of a Pulse Width Modulation (PWM) control signal, which is applied to the set of primary MOSFETs of the DC-DC converter, in accordance with the first exemplary embodiment of the present disclosure.
Figure 6D illustrates a waveform representation of a voltage, which is applied to a primary winding of a transformer of the DC-DC converter, in accordance with the first exemplary embodiment of the present disclosure.
Figure 6E illustrates a waveform representation of a voltage taken across the MOSFET QA of the set of primary MOSFETs of the DC-DC converter, in accordance with the first exemplary embodiment of the present disclosure.
Figure 6F illustrates a waveform representation of a voltage taken across the MOSFET QF of the set of secondary MOSFETs of the DC-DC converter, in accordance with the first exemplary embodiment of the present disclosure.
Figure 6G illustrates a waveform representation of an output voltage of the DC-DC converter, in accordance with the first exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION
Reference throughout the specification to “various embodiments,” “some embodiments,” “one embodiment,” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment, is included in at least one embodiment. Thus, appearances of the phrases “in various embodiments,” “in some embodiments,” “in one embodiment,” or “in an embodiment” in places throughout the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.
Referring now to figure 1, block diagram of a DC-DC converter (100) for narrow operating range is illustrated. In one embodiment, the narrow operating range is 300V-420V. The DC-DC converter (100) for narrow operating range comprises of a high voltage battery (101), an EMI filtering (102), a set of primary Metal-oxide-semiconductor field-effect transistors (MOSFETs) (103) and a set of secondary MOSFETs (105), a transformer (104), an output filtering (106), a LV load (107), a control circuit (108), a voltage supply (109). The high voltage battery (101) is used as an energy storing component. The voltage level of the high voltage battery (101) varies from 300V to 420V, depending upon the battery pack. The EMI filtering (102) is used to eliminate all the high frequency noises before entering into the DC-DC Converter.
Now referring to Figure 2, a schematic diagram of the DC-DC converter for narrow operating range is shown. The set of primary MOSFETs Q1 to Q4 (103) forms the H-bridge in the input section. The set of primary MOSFETs Q1 to Q4 (103) is triggered using a ZVS topology, wherein the ZVS topology is used to reduce the switching losses. The set of primary MOSFETs Q1 to Q4 (103) are high voltage and low current devices. The H-bridge is used to convert the pure DC into high frequency AC, which is fed to the transformer (104), wherein the transformer is a high frequency transformer. The high frequency transformer is required to step down the high-level AC voltage to low-level AC voltage. The low-level AC voltage is fed to a set of secondary MOSFETsQ5 to Q6 (105). The set of secondary MOSFETs Q5 to Q6 (105) is used for rectification of lower AC voltage. The transformer (104) have a core with the primary windings and the secondary windings. The transformer (104) is configured to achieve leakage inductance by providing a predefined air gap between the primary windings and the secondary winding of the core of the said transformer (104). The area of the primary windings of the transformer (104) is greater than the area of the secondary windings.
In one embodiment, the leakage inductance is achieved by providing the predefined air gap having a length of 2 mm between a primary winding and a secondary winding of the transformer (104). However, as the air gap increases, the leakage inductance also increases, which cause the spikes in the current and voltage waveforms.
Now referring to figure 3, the switching current and the voltage waveforms with the predefined air-gap of 2mm between primary winding and secondary winding of a transformer, in accordance with an embodiment of the present disclosure are illustrated. As shown in the Figure 2, the leakage inductance is observed by the leading-edge slope of the current waveform. It is observed that as the air-gap increases, the leakage inductance increases, causing spikes in the current and voltage waveforms.
Now referring back to figure 1 and figure 2, the voltage spikes is removed by output filter (106). The output filter (106) contains an inductor and a capacitor. The output filter (106) is used to filter out the ripple from output obtained. The inductor is connected in series with a load to reduce the output current ripple. The capacitor is connected in parallel, which help to smoothen the output voltage. Addition of capacitors in parallel with Cout reduce the effect of voltage spikes that are generated due to air-gap of 2mm. If current spikes are generated in the output current, addition of inductor in series with line would reduce the air-gap effects.
The LV load consists of all the axillaries of EV working at lower voltage. The control circuit (106) of the DC-DC converter generates the gate pulses for both the set primary MOSFETs Q1 to Q4(103) and the set of secondary MOSFETs Q5 to Q6 (105). Further, the 24v supply is configured to supply power to the control circuit (108).
Now referring to the Table 1 Comparative data of leakage inductance for various air-gaps are given as follows:
Table 1 Comparative data of leakage inductance for various air-gaps
Input voltage Range 300V-420V 300V-420V 200V-300V 100V-200V
Output voltage range 22V-30V 15V-30V 20V-30V 22V-30V
Air-gap 11mm 2mm 4mm 6mm
Number of turns 7T 7T 7T 7T
Leakage inductance of transformer 9uH 3.5uH 5.2uH 6.5uH
Shim inductance Not required Not required Not required Not required
As shown in the table 1, for the input voltage range of 100V-200V, the leakage inductance is 6.5uH. For the input voltage range of 200V-300V, the leakage inductance is 5.2 uH. Therefore, it has been experimentally observed that as value of leakage inductance is more, the operating range of transformer is narrow. This leads to increase in the transformer loss.
For input voltage range of 300-410V, if air gap of 11mm is provided between the primary winding and the secondary winding, then leakage inductance of transformer is 9uH. For input voltage range of 300-410V, if air gap of 2mm is provided between the primary winding and the secondary winding, then leakage inductance of transformer is 3.5uH. Therefore, it is observed that if the air gap between the primary windings and secondary winding increases, the leakage inductance also increases. However, increase in the leakage inductance of transformer may increase loss in the transformer. It must be noted that the major issue faced by existing DC-DC converter is conversion efficiency of the transformer. When the leakage inductance is used for calculating ZVS range, the primary MOSFETs fails due to increase in the junction temperature. Further, when the leakage inductance is calculated using an average current, it results in an insufficient value of leakage inductance. When the leakage inductance is calculated using peak current instead of the average current, the value of the leakage inductance is excessively high. However, introducing such leakage inductance with higher leakage inductance in the transformer that results in higher core losses. Therefore, the air gap of 2mm between the primary winding and the secondary winding of the transformer may achieve required leakage inductance of 3.5uH. without increasing the transformer loss and without using additional components.
The DC-DC converter for narrow operating range in the Electric Vehicle (EV) help to design the optimized system with better efficiency. In one embodiment, the DC-DC converter for narrow operating range is designed less bulky and having better space.
The leakage inductance is achieved by providing predefined air gap having a length of 2 mm between the primary winding and the secondary winding of the transformer (104), wherein the achieved leakage inductance is 3.5uH. The achieved leakage inductance range is changed by change in ratio of the primary windings and the secondary windings of the transformer (104). The ratio of the turns between the primary windings and the secondary windings affect the leakage inductance range. The equation of turns ratio is, Ns/Np=Vo/(Vin*Dmax)
Wherein, Secondary turns, Ns= 1 is constant
Output voltage, Vo is maintained constant
Duty cycle, Dmax is kept constant
Thus, equation becomes, Vin?Np
Hence, by changing primary winding turns, input voltage is changed. Therefore, the leakage inductance range is affected by change in ratio of the primary windings and the secondary windings of the transformer (104).
Now referring to figure 4A-4B, the bobbin E70 flat link transformer is illustrated, in accordance with the embodiment of the present disclosure. E cores is used in the power transformers and low signal applications. These cores are supplied with different air gaps, and inductance factor (AL) values, wherein the inductance factor (AL) depends on the size of the air gap in the middle leg. Further, the area of the primary windings of the transformer is greater than the area of the secondary windings.
In a first exemplary embodiment, the DC-DC converter as shown in figure 5 comprise of the input voltage 420V, input capacitance is Cin 20uF, Lout is 1.6uF, magnetizing inductance of the transformer Lm=700 uF, no. of turns of the primary winding Np=6, no. of turns of the secondary winding Ns =1 and an output voltage Vo=28.8V.
Further, the DC-DC converter in accordance with the first embodiment of the present disclosure comprises an output power 4000W max, output current 4000/28.8=148A, allowable output voltage transient 2V, Full load efficiency =95%,
inductor (Lout) switching frequency is 200kHz typical.
Referring to Figure 6A, a waveform representation of a control signal, which is applied to the set of primary MOSFETs of the DC-DC converter is illustrated, in accordance with the first exemplary embodiment of the present disclosure.
Referring to Figure 6B, a waveform representation of input current, which is applied to the set of primary MOSFETs of the DC-DC converter is illustrated, in accordance with the first exemplary embodiment of the present disclosure.
Referring to Figure 6C a waveform representation of a Pulse Width Modulation (PWM) control signal, which is applied to the set of primary MOSFETs of the DC-DC converter is illustrated, in accordance with the first exemplary embodiment of the present disclosure.
Referring to Figure 6D a waveform representation of a voltage, which is applied to a primary winding of a transformer of the DC-DC converter is illustrated, in accordance with the first exemplary embodiment of the present disclosure.
Referring to Figure 6E a waveform representation of a voltage taken across the MOSFET QA of the set of primary MOSFETs of the DC-DC converter is illustrated, in accordance with the first exemplary embodiment of the present disclosure.
Referring to Figure 6F a waveform representation of a voltage taken across the MOSFET QF of the set of secondary MOSFETs of the DC-DC converter is illustrated, in accordance with the first exemplary embodiment of the present disclosure.
Referring to Figure 6G a waveform representation of an output voltage of the DC-DC converter is illustrated, in accordance with the first exemplary embodiment of the present disclosure.
The foregoing description shall be interpreted as illustrative and not in any limiting sense. A person of ordinary skill in the art would understand that certain modifications could come within the scope of this disclosure. The embodiments, examples and alternatives of the preceding paragraphs or the description and drawings, including any of their various aspects or respective individual features, 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.

, Claims:WE CLAIM:
1. A DC-DC converter (100) for narrow operating range, characterized in that, the DC-DC converter (100) comprises:
a high voltage battery (101);
a set of primary Metal-oxide-semiconductor field-effect transistor (MOSFETs) (103) and a set of secondary MOSFETs (105);
a transformer (104) having a core with a primary winding and a secondary winding, wherein a predefined air gap is provided in between the primary windings and the secondary winding of the core of the said transformer (104) for achieving the leakage inductance, wherein the area of the primary windings of the transformer (104) is greater than the area of the secondary windings.
2. The DC-DC converter (100) for narrow operating range as claimed in claim 1, wherein the predefined air gap of 2 mm is provided in between the primary winding and the secondary winding of the transformer (104) for achieving the leakage inductance.
3. The DC-DC converter (100) for narrow operating range as claimed in claim 1, wherein the leakage inductance is 3.5 µH.
4. The DC-DC converter (100) for narrow operating range as claimed in claim 3, wherein the range of the leakage inductance range is affected by change in turns ratio of the primary windings and the secondary windings of the transformer (104).
5. The DC-DC converter (100) for narrow operating range as claimed in claim 1, wherein the DC-DC converter comprising of one or more EMI filters for eliminating high frequency noises from an input DC voltage.
6. The DC-DC converter (100) for narrow operating range as claimed in claim 1, wherein the set of primary MOSFETs are configured to convert the input DC voltage to a high AC voltage.

7. The DC-DC Converter (100) for narrow operating range as claimed in claim 1, wherein the high voltage battery is configured to operate in the operating range 300 V to 420V .

Dated this 09th day of December 2022

Deepak Pawar
Agent for the applicant
IN/PA-2052