FORM2
THE PATENTS ACT 1970
39 OF 1970
&
THE PATENT RULES 2003
COMPLETESPECIFICATION
(SEE SECTIONS 10 & RULE 13)
1. TITLEOFTHEINVENTION
“ON-BOARD CHARGING SYSTEM FOR ELECTRIC VEHICLES”
2. APPLICANTS
(a) Name: Varroc Engineering Limited
(b) Nationality: Indian
(c) Address: L-4, Industrial Area,
Waluj MIDC, Aurangabad-431136,
Maharashtra, India
(a) Name: Indian Institute of Technology Bombay
(b) Nationality: Indian
(c) Address: Indian Institute of Technology Bombay, Adi Shankaracharya Marg, Powai, Mumbai-400 076, Maharashtra, India
3. PREAMBLETOTHEDESCRIPTION
COMPLETESPECIFICATION
The following specification particularly describes the invention and the manner in
which it is to be performed

TECHNICAL FIELD
The present disclosure in general relates to electric vehicles, and more particularly to an on-board charging system for electric vehicles.
BACKGROUND
The subject matter discussed in the background section should not be assumed to be prior art merely as a result 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.
The applications involving renewable energy sources like solar, hydrogen, wind and tidal along with electric vehicles (EVs) are gaining significance in the current scenario. All these applications demand the use of energy storage devices like batteries to ensure uninterrupted system operation. In these applications, there exist cases where the source availability and load demand have a significant mismatch. In these situations, energy storage devices play a significant role by supporting the load during unavailability of source by storing the energy from the source. The situation is true in the case of auxiliary loads of EV, residential photovoltaic (PV) applications, and tidal and wind energy-based systems, where the source energy is available for limited duration and the load demands may be at different times. In EVs, there are two batteries, namely a high voltage (HV) traction battery to drive the motor and a low voltage (LV) battery to support the auxiliary loads. The utility grid charges the HV battery and LV battery simultaneously when plugged into supply. However, most of the LV battery charging takes place from the HV battery during vehicle movement when the utility grid is not available.
Figure 1A illustrates an exemplary conventional approach of using an individual converter for separate applications, according to a prior art solution. Figure 1B

illustrates an exemplary single integrated multi-port converter for interfacing different sources/storage/loads, according to another prior art solution.
As illustrated in Fig. 1A, most industrial applications use separate power converters for interfacing one dc source with a dc load. This improves reliability and reduces circuit level and control level complexities. However, separate power converters for individual power conversion lead to poor power density and higher costs. Integrated power converters interfacing different dc sources and dc loads, known as multi-port converters, allow improvement in power density and reduces cost, whenever multiple dc sources/storage/loads are present in a system. An efficient integrated circuit topology has to be designed to interface different dc sources/storages/loads effectively. Complexity arises due to the fact that the specifications of different sources and the requirements of different loads are variable. Thus, a single converter, as shown in Fig. 1(b), catering to all these requirements could possibly involve complex circuit and control implementation.
Most power conversion applications demand the use of isolated converters involving transformers to match different voltage levels with better efficiency, especially if there is a huge difference in voltage (on the contrary, non-isolated converters have lesser efficiencies when the input-output voltage ratio is very high). In addition, the transformer provides isolation among different dc sources/storage/loads. Thus, an isolated multi-port converter is required to meet the isolation and efficiency requirements of power conversion.
Onboard charging of HV battery and LV battery from utility grid is an example of a multi-port converter application. In EVs, an efficient three-port dc-dc converter is required for interfacing the rectified utility grid voltage with the HV battery and LV battery.
SUMMARY
This summary is provided to introduce concepts related to on-board charging systems for electric vehicles. 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.
In an embodiment of the present disclosure, an on-board charging system for electric vehicles (EVs) is described. The on-board charging system comprises an on-board charger (OBC) having an input ac port, a first output port operatively coupled to a first battery, and a second output port operatively coupled to a second battery. The OBC includes a three-port dc-dc converter coupled to an output of a rectifier stage of the on-board charging system, the first output port, and the second output port; two two-winding transformers; and a power transfer sub-system to transfer power across the three ports of dc-dc converter. The three-port dc-dc converter comprises a first converter sub-system, a second converter sub-system, and a third converter sub-system connected to the two two-winding transformers and the power transfer sub-system via a common bridge leg to facilitate transfer of power across the three port dc-dc converter. The power transfer sub-system comprises one of: a first inductor coupled between the first converter sub-system and the second converter sub-system, and a second inductor coupled between the second converter sub-system and the third converter sub-system, or a single inductor in a line connecting a common bridge leg with the two two-winding transformers.
To further clarify advantages and features of the present disclosure, a more particular description of the disclosure will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the disclosure and are therefore not to be considered limiting of its scope. The disclosure will be described and explained with additional specificity and detail with the accompanying drawings.
BRIEF DESCRIPTION OF FIGURES
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 1A illustrates an exemplary conventional approach of using an individual converter for separate applications, according to a prior art solution.
Figure 1B illustrates an exemplary single integrated multi-port converter for interfacing different sources/storage/loads, according to another prior art solution.
Fig. 2A illustrates a general architecture of an on-board charging system including the proposed three-port dc-dc converter for an electric vehicle, according to various embodiments of the present disclosure.
Fig. 2B illustrates a general architecture of the proposed three-port dc-dc converter of an on-board charger (OBC) of the on-board charging system for an electric vehicle, according to various embodiments of the present disclosure.
Figure 3 illustrates a three-port power converter topology of an on-board charging system of an electric vehicle, where the first converter sub-system is realized with a half-bridge circuit, the second converter sub-system with a semi-active bridge circuit, and the third converter sub-system with another semi-active bridge circuit, according to an embodiment of the present disclosure.
Fig. 4 illustrates a dc-dc converter topology of the on-board charging system, showing the third converter sub-system realization with a diode bridge, in accordance with an embodiment of the present disclosure.
Fig. 5 illustrates another dc-dc converter topology of the on-board charging system, where the semi-active bridge of the third converter sub-system is realized using two low-side switches, in accordance with an embodiment of the present disclosure.
Fig. 6 illustrates yet another dc-dc converter topology of the on-board charging system, showing a single inductor-based realization of the topology discussed in Fig. 3, in accordance with an embodiment of the present disclosure.

Figure 7 illustrates yet another dc-dc converter topology of the on-board charging system, where a diode bridge is used for the third converter sub-system realization along with a single inductor approach discussed in Fig. 6, in accordance with an embodiment of the present disclosure.
Figure 8 illustrates yet another dc-dc converter topology of the on-board charging system for high-power EV applications like four-wheelers and heavy vehicles, in accordance with an embodiment of the present disclosure.
Figure 9 illustrates yet another dc-dc converter topology of the on-board charging system, where the third converter sub-system is realized with a center-tapped transformer, in accordance with an embodiment of the present disclosure.
Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have been necessarily been drawn to scale. For example, the flow charts illustrate the method in terms of the most prominent steps involved to help to improve understanding of aspects of the present disclosure. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.
DETAILED DESCRIPTION
For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the disclosure as illustrated therein being contemplated as would normally occur to one skilled in the art to which the disclosure relates. Unless otherwise defined, all technical and scientific terms used

herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this disclosure belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.
The term “some” as used herein is defined as “none, or one, or more than one, or all.” Accordingly, the terms “none,” “one,” “more than one,” “more than one, but not all” or “all” would all fall under the definition of “some.” The term “some embodiments” may refer to no embodiments or to one embodiment or to several embodiments or to all embodiments. Accordingly, the term “some embodiments” is defined as meaning “no embodiment, or one embodiment, or more than one embodiment, or all embodiments.”
The terminology and structure employed herein is for describing, teaching and illuminating some embodiments and their specific features and elements and does not limit, restrict or reduce the spirit and scope of the claims or their equivalents.
More specifically, any terms used herein such as but not limited to “includes,” “comprises,” “has,” “consists,” and grammatical variants thereof do NOT specify an exact limitation or restriction and certainly do NOT exclude the possible addition of one or more features or elements, unless otherwise stated, and furthermore must NOT be taken to exclude the possible removal of one or more of the listed features and elements, unless otherwise stated with the limiting language “MUST comprise” or “NEEDS TO include.”
Whether or not a certain feature or element was limited to being used only once, either way it may still be referred to as “one or more features” or “one or more elements” or “at least one feature” or “at least one element.” Furthermore, the use of the terms “one or more” or “at least one” feature or element do NOT preclude there being none of that feature or element, unless otherwise specified by limiting language such as “there NEEDS to be one or more . . . ” or “one or more element is REQUIRED.”

Unless otherwise defined, all terms, and especially any technical and/or scientific terms, used herein may be taken to have the same meaning as commonly understood by one having an ordinary skill in the art.
Reference is made herein to some “embodiments.” It should be understood that an embodiment is an example of a possible implementation of any features and/or elements presented in the attached claims. Some embodiments have been described for the purpose of illuminating one or more of the potential ways in which the specific features and/or elements of the attached claims fulfil the requirements of uniqueness, utility and non-obviousness.
Use of the phrases and/or terms such as but not limited to “a first embodiment,” “a
further embodiment,” “an alternate embodiment,” “one embodiment,” “an
embodiment,” “multiple embodiments,” “some embodiments,” “other
embodiments,” “further embodiment”, “furthermore embodiment”, “additional embodiment” or variants thereof do NOT necessarily refer to the same embodiments. Unless otherwise specified, one or more particular features and/or elements described in connection with one or more embodiments may be found in one embodiment, or may be found in more than one embodiment, or may be found in all embodiments, or may be found in no embodiments. Although one or more features and/or elements may be described herein in the context of only a single embodiment, or alternatively in the context of more than one embodiment, or further alternatively in the context of all embodiments, the features and/or elements may instead be provided separately or in any appropriate combination or not at all. Conversely, any features and/or elements described in the context of separate embodiments may alternatively be realized as existing together in the context of a single embodiment.
Any particular and all details set forth herein are used in the context of some embodiments and therefore should NOT be necessarily taken as limiting factors to the attached claims. The attached claims and their legal equivalents can be realized in the context of embodiments other than the ones used as illustrative examples in the description below.

Embodiments of the present disclosure will be described below in detail with reference to the accompanying drawings.
Multi-port power converters play a significant role in improving power density and reducing cost whenever multiple sources/storage/loads are present in a system. In an EV, a high voltage (HV) propulsion and a low voltage (LV) auxiliary battery supply the propulsion motor and auxiliary loads, respectively. Current industrial standards mostly demand separate power converter stages to charge HV batteries from the utility grid (OBC) and LV batteries from HV batteries (APM). An integrated multi-port converter capable of interfacing the utility grid and the two batteries could help reduce the cost and improve the power density of EVs. HV battery charging from the utility grid is usually done when the EV is not in motion. During HV battery charging, the LV battery should be isolated from the system for safety purposes. However, the LV port has to be active to support the HV battery charging process. Thus, there is a need to simultaneously supply power to the HV battery port and LV battery port during HV battery charging operation from the utility grid.
Here, the above discussed three-port dc-dc converter could simultaneously support the energy storage system and load from a source, and then independently support the load from the energy storage system alone. Here, the ac input from the utility grid is rectified into dc using a PFC rectifier circuit. The present subject matter relates to an application where the source availability and load requirements have a huge mismatch.
According to one or more embodiments, a three-port dc-dc converter of an on-board charging system is described that could be interfaced with three separate dc sources/storage/loads. This converter may be made up of one or more off-the-shelf active switches and passive/semiconductor components. The three-port dc-dc converter has two isolated dc-dc converters as sub-products. The three-port converter proposed herein provides an economical solution compared to other conventionally known three-port converters available in the market. Additionally, the proposed three-port dc-dc converter could be operated as an integrated onboard

charger capable of charging both a high voltage (HV) traction battery and a low voltage (LV) auxiliary battery from the rectified ac input. In an implementation of the three-port dc-dc converter, a first converter sub-system is connected to the output of the rectifier or the power factor correction (PFC) stage, a second converter sub-system is connected to the first dc output port operatively coupled to a first battery or a HV traction battery, and a third converter sub-system is connected to the second dc output port operatively coupled to a second battery or a LV auxiliary battery. In this particular EV application, connecting first converter sub-system and second converter sub-system alone could realize an onboard charger charging the HV battery alone from the rectified ac input. Whereas connecting the second converter sub-system and the third converter sub-system alone could realize an auxiliary power converter for charging LV auxiliary battery alone from the HV battery. Thus, in an alternative embodiment, this onboard charger and auxiliary power converter could be provided as separate systems.
According to an embodiment, an on-board charging system for electric vehicles is described which comprises a circuit consisting of three bridge cells or dc-dc converter sub-systems (which can be extended), with each bridge cell consisting of two or more power semiconductor devices or passive devices/components to facilitate unidirectional or bidirectional power flow. Further, the dc-dc converter sub-systems or the bridge cells are connected with transformers so as to facilitate power flow among the bridge cells with a combination of duty ratio and phase-shift control. The bridge cells/sub-systems’ legs are realized with one or more variations of the bridge circuits, consisting of combinations of active switches, transistors/diodes, and capacitors. Further, there exists at least one bridge cell with four or more power devices and a common leg connected to at least two different transformers to enable power transfer between the primary sides of the transformers. The bridge cell may be connected to transformer terminals through at least one leakage inductance to facilitate controlled power flow and soft switching.
Further, according to an embodiment, the present disclosure is directed towards a three-port dc-dc power converter system with one input ac port and two output dc

ports, capable of simultaneously regulating the power transfers towards both output dc ports while achieving controlled regulation of output voltages.
According to one embodiment, an on-board charger circuit of the on-board charging system may include three converter sub-systems or bridge cells connected with two two-winding transformers, such that the first converter sub-system and third converter sub-system can be realized by a combination of diodes, switches, and capacitors, while the second converter sub-system consists of two diodes, two switches, and two capacitors. The two two-winding transformers may be connected, such that the first transformer is connected between the first bridge cell and the diode leg and switch leg of the second converter sub-system, while the second transformer is connected between the third converter sub-system and switch leg and capacitor leg of the second converter sub-system. The switch leg is connected to the transformers through a leakage inductor, so as to facilitate controlled power flow and soft switching of the converter sub-systems. The second converter sub¬system acts as a full bridge interface with the first converter sub-system and a half-bridge interface with the third converter sub-system, such that the power flow is controlled by a combination of duty ratio and phase shift.
Fig. 2A illustrates a general architecture of an on-board charging system 200a including the proposed three-port dc-dc converter for an electric vehicle, according to various embodiments of the present disclosure. Fig. 2B illustrates a general architecture of the proposed three-port dc-dc converter of an on-board charger (OBC) 200b of the on-board charging system 200a for an electric vehicle, according to various embodiments of the present disclosure. Figures 2A and 2B are explained in conjunction with each other for the sake of better explanation.
During HV battery 222 and LV battery 220 charging from the utility grid, a power factor correction (PFC) rectification stage 224 is present to convert the ac grid voltage (Vg) to dc voltage at input dc port 212. Thus, the PFC or rectifier stage 224 comprises the first stage of any two-stage OBC system 200a. The output of the rectifier or PFC stage 224 forms the dc-link for OBC 200b. Hence, the multi-port dc-dc converter for an EV may be a three-port dc-dc converter interfacing the dc-

link port with the two battery ports 214 and 216 of the EV, wherein battery port 214 corresponds to charging port for LV battery 220 while the battery port 216 corresponds to charging port for LV battery 222. The three-port dc-dc converter should allow simultaneous charging of the HV battery 222 and LV battery 220 during OBC operation. The three-port dc-dc converter in auxiliary power module (APM) mode ensures LV battery 220 charging from the HV battery 222.
As depicted, the on-board charging system 200a comprises an on-board charger 200b which may include a three-port dc-dc converter, two two-winding transformers 208-210, and a power transfer sub-system to transfer power across three ports of the three-port dc-dc converter. The on-board charger 200b comprises an input ac port (at Vg), a first output port 216 operatively coupled to the HV battery 222 and a second output port operatively coupled to the LV battery 220. The three-port dc-dc converter may include three bridges/bridge cells/converter configurations/subsystems 202-206, and the power transfer sub-system comprises one/two inductors 218. In various embodiments, the three-port dc-dc converter comprises a first bridge or converter sub-system 202, a second bridge or converter sub-system 204, and a third bridge or converter sub-system 206 connected to the two two-winding transformers 208-210, and the power transfer sub-system via a common bridge leg to facilitate transfer of power across the three ports of the dc-dc converter. Each of the three converter sub-systems 202-206 may include controlled switches and/or uncontrolled devices (diodes) and/or capacitors (i.e., passive components). The first and third converter sub-systems 202 and 206 of the three converter sub-systems have two legs whose dc sides are connected to dc-1 port 212 (or output of the rectifier stage 224) and dc-3 port 214 respectively, and ac sides are connected to one winding of the two two-winding transformers 208-210. The second converter sub-system 204 has three legs of semiconductor or passive devices and whose ac side is connected to three ac nodes namely a1, a2, and a3; and dc side is connected to the dc-2 port 216 coupled to the HV battery 222. Power flow occurs from/to port 212 to/from port 216, and to/from port 214 from/to port 216 based on the active bridge principle.

Further, in an embodiment, the first converter sub-system 202 and third converter sub-system 206 are realized using one or more variations of the bridge circuit, as discussed later herein, depending upon the application. The second converter sub-system 204 may include three bridge legs, where the bridge leg connected to node a1 is realized using diodes/active switches/capacitors, the bridge leg connected to node a3 is realized using active switches/capacitors, and the bridge leg connected to node a2 which act as the common bridge leg is realized using active switches.
In one or more embodiments, the first leg, of the three legs of the second converter sub-system 204 is realized using one or more of a diode, an active switch, and a capacitor. The second leg, of the three legs of the second converter sub-system 204, which acts as the common bridge leg is realized using one or more active switches. The third leg, of the three legs of the second converter sub-system 204, is realized using one or more capacitors. The embodiments are discussed in conjunction with Figs. 3-9 of the present disclosure.
Furthermore, the OBC circuit 200b may include the power transfer sub-system which comprises either one or two inductors 218. In an embodiment, the power transfer sub-system may include a first inductor coupled between the first converter sub-system 202 and the second converter sub-system 204, and a second inductor coupled between the second converter sub-system 204 and the third converter sub¬system 206, as depicted in several figures later herein. In another embodiment, the power transfer sub-system may include a single inductor 218 in a line connecting a common bridge leg with the two two-winding transformers 208-210, as depicted in several figures later herein.
Thus, the OBC circuit 200b may include at least one inductor 218 connecting the three converter sub-systems 202-206. Thus, there are either two inductors separately between the first converter sub-system 202 and the second converter sub¬system 204, and the second converter sub-system 204 and the third converter sub¬system 206, or one single inductor in the line connecting the common bridge leg with both the transformers 208-210. The power flow across the ports 212-216

occurs in a decoupled manner. This decoupled power flow occurs at the hardware level rather than at the control implementation level.
Further, the OBC 200b is configured to control power transfer among the input ac port, the first output port 216, and the second output port 214 based on at least one of a duty cycle and a phase shift of the first converter sub-system 202, the second converter sub-system 204, and the third converter sub-system 206. Additionally, in various embodiments, a configuration of the first converter sub-system 202, the second converter sub-system 204, and the third converter sub-system 206 is configured to allow one of a three degrees, five degrees, or seven degrees of freedom to control power transfer based on the duty cycle and the phase shift of the first converter sub-system 202, the second converter sub-system 204, and the third converter sub-system 206.
Figure 3 illustrates a three-port power converter topology 300 of an on-board charging system of an electric vehicle, where the first converter sub-system 202 is realized with a half-bridge circuit, the second converter sub-system 204 with a semi-active bridge circuit, and the third converter sub-system 206 with another semi-active bridge circuit, according to an embodiment of the present disclosure. Specifically, the first converter sub-system (202) comprises a half-bridge circuit comprising a first leg of two active switches and a second leg of two capacitors, the second converter sub-system (204) comprises a semi active bridge circuit comprising three legs, wherein the three legs comprise two diodes, two capacitors, and two active switches, respectively, and the third converter sub-system (206) comprises a semi-active bridge circuit comprising a first leg of two transistors and a second leg of two active switches.
The present embodiment allows five degrees of freedom, i.e., duty cycles of switch legs of three converter sub-systems 202-206; phase shift between first and second converter sub-systems 202-204; and phase shift between second and third converter sub-systems 204-206 to ensure efficient operation. The inductances Llk1 302 and Llk2 304 may be the leakage inductances of the transformers 208-210 and could be

positioned on either side of the transformers windings. Here, the dc-1 input port 212 is the dc-link port, the dc-2 output port 216 is connected to the HV battery 222, and the dc-3 output port 214 is connected to the LV battery 220.
Thus, in the current embodiment, the OBC 200b may be configured to control power transfer among the input ac port, the first output port 216, and the second output port 214 based on a duty cycle of the first leg of the first converter sub¬system 202, a duty cycle of a second leg of the second converter sub-system 204 comprising the two active switches, a duty cycle of the second leg of the third power converter sub-system 206, a phase shift between the first converter sub-system 202 and the second converter sub-system 204, and a phase shift between the second-converter sub-system 204 and the third converter sub-system 206.
Fig. 4 illustrates a dc-dc converter topology 400 of the on-board charging system, showing the third converter sub-system 206’s realization with a diode bridge, reducing the cost of power devices and the gate driver associated with the power devices, however, having only three degrees of freedom (duty cycles of switch legs of the first converter sub-system 202 and the second converter sub-system 204, phase shift between first and second converter sub-systems 202-204.
In the case of two-wheeler/three-wheeler applications, power is not fed back from the HV battery 222 to the utility grid due to the limited capacity of the HV battery 222. The topology 400 depicted in Fig. 4 is directed towards implementation of charging systems in two-wheelers or three-wheelers.
The topology presented in Fig. 4 uses a half-bridge circuit for the first converter sub-system 202 realizations, a diode full-bridge for the third converter sub-system realization 206, and a semi-dual-active bridge for the second converter sub-system 204 realization. Specifically, the first converter sub-system 202 comprises a half-bridge circuit comprising a first leg of two capacitors and a second leg of two active switches, the second converter sub-system 204 comprises a semi-dual-active bridge comprising three legs, wherein the three legs comprise two diodes, two capacitors,

and two active switches, respectively, and the third converter sub-system 206 comprises a diode full-bridge comprising two legs each of two transistors. Thus, the topology 400 comprises four active switches, six diodes, two transformers, and four capacitors for its realization. The three converters 202-206 in the topology 400 act as pulse width modulation (PWM) converters, and the power transfer among different dc-ports 212-216 are controlled by duty cycle and phase shift among the different legs of the three converter sub-systems 202-206. These PWM converters use leakage inductance for power transfer among different ports 212-216. During HV battery charging, the second converter sub-system 204 acts like a full-bridge topology, and during LV battery charging, the second converter sub-system 204 operates as a half-bridge converter.
In operation, in these pulse-width modulation (PWM) type converters discussed above (i.e., the three-port dc-dc converter), the leakage inductance is not enough for power transfer, and usually, an additional inductor may be connected in series with the transformer for actual power transfer. Thus, in the topology shown in Fig. 4, inductors 302-304 would be included in series with the leakage inductances. In this topology 400, the duty cycle of the switch leg in the first converter sub-system 202 and the phase shift between the first converter sub-system 202 and the second converter sub-system 204 is used to control the power transferred from the dc-1 input port 212 to the HV battery output port 216. The duty cycle of the active switch leg in the second converter sub-system 204 is used for controlling the power fed to the LV battery 220 from the HV battery 222. Thus, the power fed to both dc-2 output port 216 and dc-3 output port 214 from the dc-1 input port 212 is completely decoupled even during the simultaneous operation of the three-port converter topology 400. However, in the EV application, the power fed into dc-3 output port 214 during simultaneous operation is very small compared to the power transferred to the dc-3 output port 214 during auxiliary power module (APM) operation. Thus, the duty cycle of the second converter sub-system 204 has to be maintained at a low value. This results in higher losses, as the root mean square (RMS) value of the current is high when operated at a low duty cycle value. To overcome this challenge, the third converter sub-system 206 could be realized using a semi-active bridge.

The power transferred to the dc-2 output port 216 from the dc-1 input port 212 or the input ac port could be controlled using the duty cycle of the first converter sub¬system 202 switch leg comprising two active switches, the duty cycle of the second converter sub-system 204 switch leg comprising two active switches, and the phase shift between the first converter sub-system 202 and the second converter sub¬system 204. The power supplied to the dc-3 output port 214 could now be controlled using the duty cycle of the switch leg in the third converter sub-system 206 and the phase shift between the second converter sub-system 204 and the third converter sub-system 206 in addition to the duty cycle of the switch leg in the second converter sub-system 204. Specifically, in one embodiment, the power transfer from the first output port 216 to the second output port 214 may be controlled based on a duty cycle of the active switches in the second converter sub-system 204.
Thus, the semi-active realization of the third converter sub-system 206 adds two more degrees of freedom for controlling power transfer compared to the topology shown in Fig. 4. The additional two degrees of freedom could be utilized to ensure the efficient operation of the three-port converter 400. However, the cost of switches is higher compared to diodes. In addition, switches require additional gate driver circuits for driving the switches. The bridge leg requires the use of a high-side and low-side gate driver for driving the top and bottom switches, respectively. Since these switches, being part of APM, operate at a low power level, a bootstrap circuit could be used to supply the top switch. Another alternative is to use a semi-active bridge, as shown in Fig. 4.
Fig. 5 illustrates another dc-dc converter topology 500 of the on-board charging system, where the semi-active bridge of the third converter sub-system 206 is realized using two low-side switches. In particular, similar to Fig. 3, the first converter sub-system 202 comprises a half-bridge circuit comprising a first leg of two active switches and a second leg of two capacitors, the second converter sub-system 204 comprises a semi active bridge circuit comprising three legs, wherein the three legs comprise two diodes, two capacitors, and two active switches,

respectively, and the third converter sub-system 206 comprises a semi-active bridge circuit comprising two legs, each of the two legs comprising a low-side active switch.
The illustrated topology allows seven degrees of freedom (duty cycles of switch legs of first and second converter sub-systems 202-204, duty cycles of switches S5 and S6, phase shift between first and second converter sub-systems 202-204 , phase shift between second and third converter sub-systems 204-206, and phase shift between switching legs having S5 and S6).Thus, more specifically, in the current embodiment, the OBC 200b is configured to control power transfer among the input ac port, the first output port 216, and the second output port 214 based on a duty cycle of the first leg of the first converter sub-system 202, a duty cycle of a second leg of the second converter sub-system 204 comprising the two active switches, a duty cycle of the two low-side active switches of the third power converter sub-system 206, a phase shift between the second converter sub-system 204 and the third converter sub-system 206, and a phase shift between the two legs of the third converter sub-system 206.
Fig. 5 shows semi-active bridge realization using only low-side switches for the third converter sub-system 206. This topology 500 is useful for other three-port converter operations other than EV applications, where the dc-3 output port 214 could be at a higher power level. In this case, both the bottom switches could be operated using low-side gate drivers. Here duty cycle of both switches of the third converter sub-system 206 is independent as they are present in different switching legs. However, the topologies shown in previous and current Figures involve the use of four magnetic cores (two transformers and two inductors). One inductor could be reduced by connecting a single inductor on the middle switching node, as shown in Fig. 6.
Fig. 6 illustrates yet another dc-dc converter topology 600 of the on-board charging system, showing a single inductor-based realization of the topology discussed in Fig. 3. Referring to Fig. 6’s topology 600, the simultaneous power transfer to dc-2 output port 216 and dc-3output port 214 from dc-1 input port 212 are coupled due

to the presence of a single inductor 602. Here, the power transfer to the dc-2 output port 216 could be controlled by the duty cycle of the switch leg of the first converter sub-system 202, and the power transferred to the dc-3 output port 214 could be controlled using the duty cycle of the switch leg of the third converter sub-system 206. This topology 600 ensures a reduction in the total volume due to a reduction in the number of magnetic components.
Figure 7 illustrates yet another dc-dc converter topology 700 of the on-board charging system, where a diode bridge is used for the third converter sub-system 206’s realization along with a single inductor approach discussed in Fig. 6. Referring to Fig. 7, the most compact and cheapest solution for the three-port converter realization is depicted, where a diode bridge is used for the third converter sub-system 206 realization along with a single inductor approach. Here, the power transfer during simultaneous operation requires an advanced control approach. This advanced control approach should ensure proper decoupling of power to ensure that the required power is fed to both the dc-2 output port 216 and dc-3 output port 214 ports from the dc-1 input port 212. This is achieved by online selection of combination of duty ratio of bridge legs and phase shift between them.
High-power EVs demand the use of a full-bridge configuration for the first converter sub-system 202 realization. At these higher power levels, power could be fed back into the utility grid from the HV battery 222 by replacing diodes in the second converter sub-system 204 with bidirectional switches. Thus, for high-power EV applications like four-wheelers and heavy vehicles, the three-port converter could be modified, as shown in Fig. 8.
Specifically, Fig. 8 illustrates the use of four active switches for the second converter sub-system 204’s realization, full bridge realization of the first converter sub-system 202 suitable for four-wheeler EV applications and allowing bidirectional power flow from dc-2 output port 216. More specifically, the first converter sub-system 202 comprises a first leg of two active switches and a second leg of another two active switches, the second converter sub-system 204 comprises

three legs, wherein the three legs comprises two active switches, another two active switches, and two capacitors, respectively, and the third converter sub-system 206 comprises a diode full-bridge comprising two legs each of two transistors.
Here, the power flow from dc-1 port to dc-2 output port 216 is controlled by using duty cycle of four switches of both the first converter sub-system 202 and the second converter sub-system 204 (i.e., the first and second legs of each of 202 and 204), phase shift among the first and second legs of each of the first converter sub¬system 202 and the second converter sub-system 204; and the phase shift between the first converter sub-system 202 and second converter sub-system 204 allowing seven degrees of freedom for controlling the power flow from dc-1 port 212 to dc-2 port 216. Power transfer from dc-2 output port 216 to dc-3 output port 214 is controlled using duty cycle of the active switches of the second converter sub¬system 204. Thus, for the converter discussed in Fig. 8, there are seven degrees of freedom in total.
The diode bridge in the third converter sub-system 206 could also be realized using a center-tapped diode rectifier for high current, low voltage applications like APM. However, it requires the use of a center-tapped transformer, which is complex to design. The third converter sub-system 206 is realized with a center-tapped transformer is illustrated in Fig. 9.
Specifically, Fig. 9 depicts the OBC comprising: the first converter sub-system 202 which comprises a half-bridge circuit comprising a first leg of two active switches and a second leg of two capacitors, the second converter sub-system 204 which comprises a semi active bridge circuit comprising three legs, wherein the three legs comprise two diodes, two capacitors, and two active switches, respectively, and the third converter sub-system 206 which comprises a center-tapped rectifier configuration, reducing a number of switching devices due to a center-tapped transformer. Thus, the realization of the third converter sub-system 206 is performed using center-tapped rectifier configuration, reducing the number of switching devices by adding a complex center-tapped transformer in circuit. The

power transfer between dc-1 port and dc-2 output port 216 is controlled using duty cycle of switches on the first converter sub-system 202 and phase shift between first converter sub-system 202 and second converter sub-system 204. The power transfer between dc-2 output port 216 to dc-3 output port is controlled using duty cycle of active switches of second converter sub-system 204. In this topology, there are three degrees of freedom, i.e., the duty cycle of bridge leg of first and second converter sub-system and the phase shift between first converter sub-system 202 and second converter sub-system 204.
The above discussed topologies for feeding power from/to different dc sources/storages/loads are presented considering a specific application of integrated onboard EV chargers for multi-port converter realization, where the dc-1 input port is connected to the dc-link, the dc-2 output port is connected to the HV battery, and the dc-3 output port is connected to the auxiliary battery. In an exemplary embodiment, the following workable ranges may be chosen for the topologies.

Sr. No. Parameter Workable range
1 dc-1 port voltage range (300-450) V
2 dc-2 port nominal voltage range (48-108) V
3 dc-3 port nominal voltage range (12-15) V
4 Peak output power supplied to dc-2 port (1.5-3.3) kW
5 Peak output power supplied to dc-3 port (200-500) W
6 Output voltage ripple in dc-2 and dc-2 port <2.5%
7 Output current ripple in dc-2 and dc- <10%

2 port
8 Peak efficiency >95%
9 Operating ambient temperature range -20 to +60oC
The aforementioned illustrated embodiments offer the following advantages over the conventional multi-port converters for charging systems, which include but are not limited to:
The three-port converter discussed is unique and provides an economical solution compared to other three-port converters conventionally available in the market due to usage of off-the-shelf semiconductor/passive components. Additionally, the developed three-port converter could be developed as an integrated onboard charger capable of charging both high voltage (HV) traction battery and low voltage (LV) auxiliary battery.
Further, the presented converter does not involve the use of multi-winding transformer, which are complex to design and has more weight and occupies more volume unlike two separate transformers used here. Additionally, the presented converter does not involve the use of lossy relays and extra switches to change mode from HV battery charging to LV battery charging, thereby, allowing efficient operation.
Furthermore, the converter presented here does not involve the use of resonant converter topologies which have low efficiency when operated away from the nominal operating voltage. Thus, for applications requiring large variation in voltages, the proposed converter could be employed for better efficiency. Moreover, the presented converter does not involve multi stage power conversion stages. Thus, the converter efficiency is better.

Various modifications to the embodiments will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. However, one of ordinary skill in the art will readily recognize that the present disclosure is not intended to be limited to the embodiments illustrated but is to be accorded the widest scope consistent with the principles and features described herein.
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.

We Claim:
1. An on-board charging system (200a) for electric vehicles (Evs), comprising:
an on-board charger (OBC) (200b) having an input ac port, a first output port (216) operatively coupled to a first battery (222), and a second output port (214) operatively coupled to a second battery (220), wherein said OBC (200b) includes:
a three-port dc-dc converter coupled to an output of a rectifier stage (224) of the on-board charging system (200a), the first output port (216), and the second output port (214);
two two-winding transformers (208, 210); and
a power transfer sub-system to transfer power across the three ports of dc-dc converter;
wherein the three-port dc-dc converter comprises:
a first converter sub-system (202), a second converter sub-system (204), and a third converter sub-system (206) connected to the two two-winding transformers (208, 210) and the power transfer sub-system via a common bridge leg to facilitate transfer of power across the three port dc-dc converter; and
wherein the power transfer sub-system comprises one of:
a first inductor coupled between the first converter sub-system (202) and the second converter sub-system (204), and a second inductor coupled between the second converter sub-system (204) and the third converter sub¬system (206), or
a single inductor (218) in a line connecting a common bridge leg with the two two-winding transformers (208, 210).
2. The on-board charging system (200a) as claimed in claim 1, wherein each of the
first converter sub-system (202) and the third converter sub-system (206) have two

legs of semiconductor or passive devices whose dc sides are connected to the output of the rectifier stage (224) and the second output port (214) respectively, and whose ac sides are connected to one winding of the two two-winding transformers (208, 210), and wherein the second converter sub-system (204) comprises three legs of semiconductor or passive devices whose ac side is connected to three ac nodes and dc side is connected to the first output port (216).
3. The on-board charging system (200a) as claimed in claim 2, wherein:
a first leg, of the three legs of the second converter sub-system (204), is realized using one or more of a diode, an active switch, and a capacitor,
a second leg, of the three legs of the second converter sub-system (204), which acts as the common bridge leg is realized using one or more active switches, and
a third leg, of the three legs of the second converter sub-system (204), is realized using one or more capacitors.
4. The on-board charging system (200a) as claimed in claim 1, wherein the OBC (200b) is configured to control power transfer among the input ac port, the first output port (216), and the second output port (214) based on at least one of a duty cycle and a phase shift of the first converter sub-system (202), the second converter sub-system (204), and the third converter sub-system (206).
5. The on-board charging system (200a) as claimed in claim 4, wherein a configuration of the first converter sub-system (202), the second converter sub-system (204), and the third converter sub-system (206) is configured to allow one of a three degrees, five degrees, or seven degrees of freedom to control power transfer based on the duty cycle and the phase shift of the first converter sub-system (202), the second converter sub-system (204), and the third converter sub-system (206).
6. The on-board charging system (200a) as claimed in claim 1, wherein:

the first converter sub-system (202) comprises a half-bridge circuit comprising a first leg of two capacitors and a second leg of two active switches,
the second converter sub-system (204) comprises a semi-dual-active bridge comprising three legs, wherein the three legs comprise two diodes, two capacitors, and two active switches, respectively, and
the third converter sub-system (206) comprises a diode full-bridge comprising two legs each of two transistors.
7. The on-board charging system (200a) as claimed in claim 6, wherein during charging of the first battery, the second converter sub-system (204) is configured to be operated as a full-bridge topology, and wherein during charging of the second battery, the second converter sub-system (204) is configured to be operated as a half-bridge converter topology.
8. The on-board charging system (200a) as claimed in claim 6, wherein the OBC (200b) is configured to:
control power transfer from the input ac port to the first output port (216) based on a duty cycle of the second leg of the first converter sub-system (202), and a phase shift between the first converter sub-system (202) and the second converter sub-system (204); and
control power transfer from the first output port (216) to the second output port (214) based on a duty cycle of the active switches in the second converter sub¬system (204).
9. The on-board charging system (200a) as claimed in claim 1, wherein:
the first converter sub-system (202) comprises a half-bridge circuit comprising a first leg of two active switches and a second leg of two capacitors,
the second converter sub-system (204) comprises a semi active bridge circuit comprising three legs, wherein the three legs comprise two diodes, two capacitors, and two active switches, respectively, and

the third converter sub-system (206) comprises a semi-active bridge circuit comprising a first leg of two transistors and a second leg of two active switches.
10. The on-board charging system (200a) as claimed in claim 9, wherein the OBC
(200b) is configured to:
control power transfer among the input ac port, the first output port (216), and the second output port based on a duty cycle of the first leg of the first converter sub-system (202), a duty cycle of a second leg of the second converter sub-system (204) comprising the two active switches, a duty cycle of the second leg of the third power converter sub-system (206), a phase shift between the first converter sub¬system (202) and the second converter sub-system (204), and a phase shift between the second-converter sub-system (204) and the third converter sub-system (206).
11. The on-board charging system (200a) as claimed in claim 1, wherein:
the first converter sub-system (202) comprises a half-bridge circuit comprising a first leg of two active switches and a second leg of two capacitors,
the second converter sub-system (204) comprises a semi active bridge circuit comprising three legs, wherein the three legs comprise two diodes, two capacitors, and two active switches, respectively, and
the third converter sub-system (206) comprises a semi-active bridge circuit comprising two legs, each of the two legs comprising a low-side active switch.
12. The on-board charging system (200a) as claimed in claim 9, wherein the OBC
(200b) is configured to:
control power transfer among the input ac port, the first output port (216), and the second output port (214) based on a duty cycle of the first leg of the first converter sub-system (202), a duty cycle of a second leg of the second converter sub-system (204) comprising the two active switches, a duty cycle of the two low-side active switches of the third power converter sub-system (206), a phase shift between the second converter sub-system (204) and the third converter sub-system

(206), and a phase shift between the two legs of the third converter sub-system (206).
13. The on-board charging system (200a) as claimed in claim 1, wherein:
the first converter sub-system (202) comprises a first leg of two active switches and a second leg of another two active switches,
the second converter sub-system (204) comprises three legs, wherein the three legs comprises two active switches, another two active switches, and two capacitors, respectively, and
the third converter sub-system (206) comprises a diode full-bridge comprising two legs each of two transistors.
14. The on-board charging system (200a) as claimed in claim 13, wherein the OBC is configured to control power transfer among the input ac port, the first output port (216), and the second output port (214) based on a duty cycle of the first leg and the second leg of the first converter sub-system (202), a duty cycle of the first leg and the second leg of the second converter sub-system (204), a phase shift between the first leg and the second leg of the first converter sub-system (202), a phase shift between the first leg and the second leg of the second converter sub-system (204), and a phase shift between the first converter sub-system (202) and the second converter sub-system (204).
15. The on-board charging system (200a) as claimed in claim 1, wherein:
the first converter sub-system (202) comprises a half-bridge circuit comprising a first leg of two active switches and a second leg of two capacitors,
the second converter sub-system (204) comprises a semi active bridge circuit comprising three legs, wherein the three legs comprises two diodes, two capacitors, and two active switches, respectively, and
the third converter sub-system (206) comprises a center-tapped rectifier configuration, reducing a number of switching devices due to a center-tapped transformer.

16. The on-board charging system (200a) as claimed in claim 15, wherein the OBC is configured to control power transfer among the input ac port, the first output port (216), and the second output port (214) based on a duty cycle of bridge legs of the first (202) and second converter sub-systems (204) and a phase shift between the first (202) and second converter sub-systems (204).