DESC:ARRANGEMENT FOR CHARGING SWAPPABLE POWER PACKS
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority from Indian Provisional Patent Application No. 202321037173 filed on 30/05/2023, the entirety of which is incorporated herein by a reference.
TECHNICAL FIELD
The present disclosure generally relates to swappable power pack charging. The present disclosure particularly relates to an arrangement for charging swappable power pack of an electric vehicle.
BACKGROUND
Recently, there has been a rapid development in electric vehicles because of their ability to resolve pollution-related problems and serve as a clean mode of transportation. Generally, electric vehicles include a battery pack, power pack, and/or combination of electric cells for storing electricity required for the propulsion of the vehicles. The electrical power stored in the battery pack of the electric vehicle is supplied to the traction motor for moving the electric vehicle. Once the electrical power stored in the battery pack of the electric vehicle is depleted, the battery pack is required to be charged from a power source or by replacing the depleted battery pack with a fully charged battery pack.
The replaceable battery packs are also known as swappable battery packs and resolve the problems of charger availability and range anxiety associated with fixed battery packs. Moreover, the swappable battery packs may also solve the problem high initial cost of ownership of the electric vehicles. Since the battery is the most expensive component of the electric vehicle, the cost associated with the ownership of the battery pack may be eliminated by getting a swappable battery as a service.
However, the swappable battery packs also require infrastructure in terms of battery swapping stations. The battery swapping stations convert the electrical energy received from the grid to charge the swappable battery packs. Furthermore, the electric vehicle itself requires a power converter to convert the electrical energy stored in the battery pack for driving the traction motor. Moreover, if the swappable battery pack is required to be charged with a charger, while being in the electric vehicle, the charger would also require a suitable power converter to convert the electrical energy received from the power source (grid) to charge the swappable battery pack. Moreover, the domestic uninterrupted power supply systems have also recently started being used for charging the swappable battery packs, while delivering power backup as and when required. However, the domestic uninterrupted power supply systems would also require a power converter to convert the electrical energy received from the domestic AC supply to charge the swappable battery packs and convert the electrical energy stored in the swappable battery pack to provide power backup for the domestic load. Such arrangements are costly as multiple sets of power converters are required to either charge or utilize the charged swappable battery pack. Moreover, a lot of electronic components are redundant on the charging equipment side when the swappable battery is being utilized for powering up electric equipment (either mobility or fixed). Similarly, a lot of electronic components are redundant on the discharging equipment side (mobility or fixed) when the swappable battery is being charged. Such redundancy increases the overall cost of the swappable battery ecosystem and hinders the use of swappable battery packs as clean energy storage solutions for mobility and fixed applications.
Therefore, there exists a need for an improved system for swappable battery pack charging that overcome one or more problems associated as set forth above.
SUMMARY
An object of the present disclosure is to provide an arrangement for charging plurality of swappable power packs.
In accordance with an aspect of the present disclosure, there is provided an arrangement for charging a plurality of swappable power packs. The arrangement comprises a line frequency transformer connected to a power source, a plurality of connectors for electrically connecting the plurality of swappable power packs to the line frequency transformer, and a control unit, communicably coupled to the plurality of swappable power packs.
The present disclosure provides an arrangement for charging plurality of swappable power packs. Beneficially, the arrangement of the present disclosure eliminates the need for power converters at every point of interaction (either charging or discharging) of the swappable battery pack. Furthermore, the arrangement of the present disclosure is advantageous in terms of reducing the costs of the clean energy storage ecosystem. Beneficially, the arrangement of the present disclosure is compact in size as it does not contain additional power converters. Beneficially, the arrangement of the present disclosure comprises minimal electronic components. Beneficially, the arrangement of the present disclosure is implemented in a domestic uninterrupted power supply. Beneficially, the arrangement enables simple electronics architecture of the domestic uninterrupted power supply. Beneficially, the arrangement may be implemented in a battery swapping station.
Additional aspects, advantages, features, and objects of the present disclosure would be made apparent from the drawings and the detailed description of the illustrative embodiments constructed in conjunction with the appended claims that follow.
It will be appreciated that features of the present disclosure are susceptible to being combined in various combinations without departing from the scope of the present disclosure as defined by the appended claims.
BRIEF DESCRIPTION OF DRAWINGS
The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the present disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those in the art will understand that the drawings are not to scale. Wherever possible, like elements have been indicated by identical numbers.
Embodiments of the present disclosure will now be described, by way of example only, with reference to the following diagrams wherein:
Figure 1 illustrates a block diagram of an arrangement for charging swappable power packs, in accordance with an aspect of the present disclosure.
Figure 2 illustrates a circuit diagram of the arrangement for charging swappable power packs, in accordance with another aspect of the present disclosure.
In the accompanying drawings, an underlined number is employed to represent an item over which the underlined number is positioned or an item to which the underlined number is adjacent. A non-underlined number relates to an item identified by a line linking the non-underlined number to the item. When a number is non-underlined and accompanied by an associated arrow, the non-underlined number is used to identify a general item at which the arrow is pointing.
DETAILED DESCRIPTION
The following detailed description illustrates embodiments of the present disclosure and ways in which they can be implemented. Although some modes of carrying out the present disclosure have been disclosed, those skilled in the art would recognize that other embodiments for carrying out or practicing the present disclosure are also possible.
The description set forth below in connection with the appended drawings is intended as a description of certain embodiments of an arrangement for charging swappable power pack and is not intended to represent the only forms that may be developed or utilized. The description sets forth the various structures and/or functions in connection with the illustrated embodiments; however, it is to be understood that the disclosed embodiments are merely exemplary of the disclosure that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.
While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure.
The terms “comprise”, “comprises”, “comprising”, “include(s)”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, or system that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or system. In other words, one or more elements in a system or apparatus preceded by “comprises... a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or apparatus.
In the following detailed description of the embodiments of the disclosure, reference is made to the accompanying drawings which are shown by way of illustration-specific embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, not to be taken in a limiting sense.
The present disclosure will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the description with unnecessary detail.
As used herein, the terms “electric vehicle”, “EV”, and “EVs” are used interchangeably and refer to any vehicle having stored electrical energy, including the vehicle capable of being charged from an external electrical power source. This may include vehicles having batteries that are exclusively charged from an external power source, as well as hybrid vehicles which may include batteries capable of being at least partially recharged via an external power source. Additionally, it is to be understood that the ‘electric vehicle’ as used herein includes electric two-wheelers, electric three-wheelers, electric four-wheelers, electric pickup trucks, electric trucks, and so forth.
As used herein, the terms “battery pack”, “battery”, and “power pack” are used interchangeably and refer to multiple individual battery cells connected to provide a higher combined voltage or capacity than what a single battery can offer along with the necessary electronic components and circuitry required to do so. The battery pack is designed to store electrical energy and supply it as needed to various devices or systems. Battery packs, as referred herein may be used for various purposes such as power electric vehicles and other energy storage applications. Furthermore, the battery pack may include additional circuitry, such as a battery management system (BMS), to ensure the safe and efficient charging and discharging of the battery cells. The battery pack comprises a plurality of cell arrays which in turn comprises a plurality of battery cells.
As used herein, the term “battery module” refers to a plurality of individual battery cells connected to provide a higher combined voltage or capacity. The battery module is used to store the electrical energy and provide the electrical energy when required.
As used herein, the terms “integrated bi-directional power converter”, “integrated converter”, “integrated power converter”, “bi-directional power converter”, and “power converter” refers to a power electronic device that converts the alternating current (AC) to direct current (DC) or vice-versa. Preferably, the integrated converter is a switching converter that uses a semiconductor switch to convert the AC to DC or vice-versa. Beneficially, the integrated converter is more efficient than conventional linear converters.
As used herein, the term “line-frequency transformer” refers to type of transformer specifically designed to operate at the standard AC power line frequency, which is typically 50 Hz or 60 Hz depending on the region.
As used herein, the term “high voltage winding” refers to primary winding of the transformer which is on the higher voltage of the step-down transformer.
As used herein, the term “low voltage winding” refers to secondary winding of the step transfer which is on the lower voltage of the step-down transformer.
As used herein, the term “battery management system” refers to electronic device that manages charging and discharging of the plurality of battery cells of the battery module. The battery management system may monitor the voltage and current during the charging and discharging process. Furthermore, the battery management system may monitor the temperature and state of charge of the plurality of battery cells of the battery module. Moreover, the battery management system may also perform cell balancing and provide protection to the plurality of battery cells from overcharging/ over discharging.
As used herein, the terms ‘control unit and ‘processor’ are used interchangeably and refer to a computational element that is operable to respond to and process instructions that control the integrated converter. Optionally, the control unit may be a micro-controller, a complex instruction set computing (CISC) microprocessor, a reduced instruction set (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, a digital signal processor, or any other type of processing unit. Furthermore, the term “microprocessor” may refer to one or more individual processors, processing devices, and various elements associated with a processing device that may be shared by other processing devices. Furthermore, the microprocessor may be designed to handle real-time tasks with high performance and low power consumption. Furthermore, the microprocessor may comprise custom and/or proprietary processors. Beneficially, the control unit enables smart features in the arrangement implemented as domestic uninterrupted power supply.
As used herein, the term “power source” refers to an equipment supplying AC power for charging the swappable power pack. The source may supply domestic AC power.
As used herein, the term “communicably coupled” refers to a bi-directional connection between the various components of the arrangement and the power pack. The bi-directional connection between the various components of the arrangement enables the exchange of data between two or more components of the arrangement and the power pack.
As used herein, the terms “DC link capacitor bank”, “DC link capacitor”, “DC bus capacitor”, and “capacitor” are used interchangeably and refer to a plurality of capacitors that are used to smooth out the fluctuating DC voltage coming from the battery module before it is converted into AC voltage to power the electric motor. The DC link capacitor bank functions to smooth out the power between the battery module and the power converter, stabilize the DC bus voltage, and act as energy storage for transient loads.
As used herein, the terms “plurality of phase inverter legs”, “phase inverter leg”, “inverter legs”, and “phase legs” are used interchangeably and refer to individual circuit blocks of the integrated power converter which are responsible for converting the DC power into the AC power and/or the AC power into the DC power. It is to be understood that each circuit block converts DC power into one phase of AC power, thus, based on the number of phases required of AC power, the number of phase inverter legs are utilised.
As used herein, the term “gate drivers” refers to electronic components responsible for controlling the switching of Metal Oxide Semiconductor Field Effect Transistor (MOSFET) which forms switches in the power converter. It is to be understood that the gate drivers convert the control signal into precise voltage and current pulses required to turn the power electronics switches on and off rapidly. These switches may control the flow of electrical current to the electric motor, ultimately determining its speed, torque, and direction of rotation. Similarly, the switches may control the flow of the electric current to the battery module, for charging the battery module, when the swappable power pack is connected to the power source.
As used herein, the term “switches” and “plurality of switch” are used interchangeably and refers to power electronics devices that control the flow of electric power from the battery module to the electric motor and/or from the power source to the battery module. The switches are responsible for converting the DC power into AC power and/or AC power into DC power. Beneficially, MOSFETs are used as switches in the integrated power converter as the MOSFETs have low on-state resistance that helps in reducing power losses and increasing the overall efficiency of the integrated power converter. The switches may be at least one of MOSFETs, IGBTs, transistors, or a combination thereof.
As used herein, the terms “plurality of sensors” “sensor arrangement” and “sensors” are used interchangeably and refer to a configuration of sensors in the system and/or arrangement to measure, monitor, or detect specific parameters, conditions, and/or events. The plurality of sensors may comprise current sensors, voltage sensors, hall effect sensors, insulation monitoring sensors, or a combination thereof.
Figure 1, in accordance with an embodiment, describes an arrangement 100 for charging a plurality of swappable power packs 102. The arrangement 100 comprises a line frequency transformer 104 connected to a power source, a plurality of connectors 110 for electrically connecting the plurality of swappable power packs 102 to the line frequency transformer 104, and a control unit 120, communicably coupled to the plurality of swappable power packs 102.
The present disclosure provides an arrangement 100 for charging plurality of swappable power packs 102. Beneficially, the arrangement 100 of the present disclosure eliminates the need for power converters at every point of interaction (either charging or discharging) of the swappable battery pack 102. Furthermore, the arrangement 100 of the present disclosure is advantageous in terms of reducing the costs of the clean energy storage ecosystem. Beneficially, the arrangement 100 of the present disclosure is compact in size as it does not contain additional power converters. Beneficially, the arrangement 100 of the present disclosure comprises minimal electronic components. Beneficially, the arrangement 100 of the present disclosure is implemented in a domestic uninterrupted power supply. Beneficially, the arrangement 100 enable simple electronics architecture of the domestic uninterrupted power supply. Beneficially, the arrangement 100 may be implemented in a battery swapping station.
In an embodiment, the arrangement 100 comprises a plurality of charging bins to receive the plurality of swappable power packs 102 within. Beneficially, the plurality of charging bins securely holds the plurality of swappable power packs 102 during the charging.
In an embodiment, the line-frequency transformer 104 comprises a high voltage winding 104a and a plurality of low voltage windings 104b. Beneficially, the line-frequency transformer 104 operates at standard AC frequency and steps down high voltage to low voltage.
In an embodiment, each of the swappable power pack 102 comprises at least one battery module 102a, a battery management system 102b, and an integrated bi-directional power converter 106. Beneficially, the integrated bi-directional power converter 106 eliminates requirement of any electronics components or power converters in the charging infrastructure such as the arrangement 100.
In an embodiment, the plurality of low voltage windings 104b of the line-frequency transformer 104 is in electrical connection with the integrated bi-directional power converter 106 of the plurality of swappable power packs 102 via the plurality of connectors 110. Beneficially, the integrated bi-directional power converter 106 of the plurality of swappable power packs 102 receives stepped down voltage from the plurality of low voltage windings 104b to charge the at least one battery module 102a.
In an embodiment, the battery management system 102b manages charging and discharging of the at least one battery module 102a and monitors a plurality of parameters associated with the at least one battery module 102a. Beneficially, the battery management system 102b interacts with a plurality of battery cells in the battery module 102a to monitor and manage the charging and discharging of the battery module 102a. Beneficially, the battery management system 102b may prevent the overcharging and over discharging of the battery module 102a. It is to be understood that the plurality of parameters associated with the at least one battery module 102a may include charging voltage, charging current, discharging voltage, discharging current, temperature, state of charge, state of health and so on. Beneficially, the battery management system 102b manages the charging and discharging of the at least one battery module 102a based on the plurality of parameters associated with the at least one battery module 102a.
In an embodiment, the battery management system 102b is communicably coupled to the integrated bi-directional power converter 106, to communicate the monitored plurality of parameters associated with the at least one battery module 102a. Beneficially, the battery management system 102b communicate the monitored plurality of parameters associated with the at least one battery module 102a to the integrated bi-directional power converter 106 for efficient and optimized charging and discharging of the at least one battery module 102a.
In an embodiment, the battery management system 102b is communicably coupled to the control unit 120 to communicate the monitored plurality of parameters associated with the at least one battery module 102a. Beneficially, the control unit 120 enables transfer of information to at least one user device or a display unit of the arrangement 100.
In an embodiment, the integrated bi-directional power converter 106 is configured to convert DC power received from the at least one battery module 102a into AC power, and convert AC power received from the line-frequency transformer into DC power, to charge the at least one battery module 102a. Beneficially, the integrated bi-directional power converter 106 eliminates requirement of any electronics components or power converters in the charging infrastructure such as the arrangement 100 or a battery swapping station. Similarly, the integrated bi-directional power converter 106 eliminates requirement of any electronics components or power converters (inverters) at the application side of the swappable power pack 102 such as driving a traction motor.
In an embodiment, the integrated bi-directional power converter 106 comprises a DC link capacitor bank 112 connected with the battery management system 102b to minimize voltage ripple between the battery management system 102b and the integrated bi-directional power converter 106. Beneficially, the DC link capacitor bank 112 absorbs the periodic voltage and/or current spikes between the battery management system 102b and the integrated bi-directional power converter 106. It would be appreciated that the DC link capacitor bank 112 would absorb the excess amount of voltage and/or current between the battery management system 102b and the integrated bi-directional power converter 106, and would supply the same to the integrated bi-directional power converter 106 when there is a drop in voltage and/or current between the battery management system 102b and the integrated bi-directional power converter 106 and vice-versa.
In an embodiment, the integrated bi-directional power converter 106 comprises a plurality of phase inverter legs 114a, 114b, 114c, wherein each of the phase inverter leg 114a, 114b, 114c comprises a pair of switches S1, S2 and wherein the pair of switches S1, S2 of the plurality of phase inverter legs 114a, 114b, 114c perform switching operation for three phase AC to DC conversion or vice versa. Beneficially, the pair of switches switch alternatively for the functioning of the plurality of phase inverter legs 114a, 114b, 114c, to convert the DC power into three phase AC power or to convert the three phase AC power into the DC power.
In an embodiment, the switches S1, S2 of two of the plurality of phase inverter legs 114a, 114b, 114c perform switching operation for single-phase AC to DC conversion or vice versa. Beneficially, the pair of switches switch alternatively for the functioning of two of the plurality of phase inverter legs 114a, 114b, 114c, to convert the DC power into single-phase AC power or to convert the single-phase AC power into the DC power.
In an embodiment, the integrated bi-directional power converter 106 comprises a microcontroller to control the switching operation of the plurality of phase inverter legs 114a, 114b, 114c, via a plurality of gate drivers. Beneficially, the microcontroller controls the gate drivers to provide high-voltage and high-current signals needed to control the switching of the switches of the plurality of phase inverter legs 114a, 114b, 114c. Beneficially, the microcontroller allows the plurality of phase inverter legs 114a, 114b, 114c to generate the variable voltages.
Figure 2, in accordance with an embodiment, describes the arrangement 100. The arrangement 100 comprises the line frequency transformer 104 connected to the power source, the plurality of connectors 110 for electrically connecting the plurality of swappable power packs 102 to the line frequency transformer 104, and the control unit 120, communicably coupled to the plurality of swappable power packs 102. Furthermore, the line-frequency transformer 104 comprises the high voltage winding 104a and the plurality of low voltage windings 104b. Furthermore, each of the swappable power pack 102 comprises the at least one battery module 102a, the battery management system 102b, and the integrated bi-directional power converter 106. Furthermore, the plurality of low voltage windings 104b of the line-frequency transformer 104 is in electrical connection with the integrated bi-directional power converter 106 of the plurality of swappable power packs 102 via the plurality of connectors 110. Furthermore, the battery management system 102b manages charging and discharging of the at least one battery module 102a and monitors the plurality of parameters associated with the at least one battery module 102a. Furthermore, the battery management system 102b is communicably coupled to the integrated bi-directional power converter 106, to communicate the monitored plurality of parameters associated with the at least one battery module 102a. Furthermore, the battery management system 102b is communicably coupled to the control unit 120 to communicate the monitored plurality of parameters associated with the at least one battery module 102a. Furthermore, the integrated bi-directional power converter 106 is configured to convert DC power received from the at least one battery module 102a into AC power, and convert AC power received from the line-frequency transformer into DC power, to charge the at least one battery module 102a. Furthermore, the integrated bi-directional power converter 106 comprises the DC link capacitor bank 112 connected with the battery management system 102b to minimize voltage ripple between the battery management system 102b and the integrated bi-directional power converter 106. Furthermore, the integrated bi-directional power converter 106 comprises the plurality of phase inverter legs 114a, 114b, 114c, wherein each of the phase inverter leg 114a, 114b, 114c comprises the pair of switches S1, S2 and wherein the pair of switches S1, S2 of the plurality of phase inverter legs 114a, 114b, 114c perform switching operation for three phase AC to DC conversion or vice versa. Furthermore, the switches S1, S2 of two of the plurality of phase inverter legs 114a, 114b, 114c perform switching operation for single-phase AC to DC conversion or vice versa.
In the description of the present invention, it is also to be noted that, unless otherwise explicitly specified or limited, the terms “disposed,” “mounted,” and “connected” are to be construed broadly, and may for example be fixedly connected, detachably connected, or integrally connected, either mechanically or electrically. They may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present invention can be understood in specific cases to those skilled in the art.
Modifications to embodiments and combinations of different embodiments of the present disclosure described in the foregoing are possible without departing from the scope of the present disclosure as defined by the accompanying claims. Expressions such as “including”, “comprising”, “incorporating”, “have”, and “is” used to describe and claim the present disclosure are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural where appropriate.
Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the present disclosure, the drawings, and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.
,CLAIMS:WE CLAIM:
1. An arrangement (100) for charging a plurality of swappable power packs (102), wherein the arrangement (100) comprises:
- a line frequency transformer (104) connected to a power source;
- a plurality of connectors (110) for electrically connecting the plurality of swappable power packs (102) to the line frequency transformer (104); and
- a control unit (120), communicably coupled to the plurality of swappable power packs (102).
2. The arrangement (100) as claimed in claim 1, wherein the arrangement (100) comprises a plurality of charging bins to receive the plurality of swappable power packs (102) within.
3. The arrangement (100) as claimed in claim 1, wherein the line-frequency transformer (104) comprises a high voltage winding (104a) and a plurality of low voltage windings (104b).
4. The arrangement (100) as claimed in claim 1, wherein each of the swappable power pack (102) comprises:
- at least one battery module (102a);
- a battery management system (102b); and
- an integrated bi-directional power converter (106).
5. The arrangement (100) as claimed in claim 3, wherein the plurality of low voltage windings (104b) of the line-frequency transformer (104) is in electrical connection with the integrated bi-directional power converter (106) of the plurality of swappable power packs (102) via the plurality of connectors (110).
6. The arrangement (100) as claimed in claim 4, wherein the battery management system (102b) manages charging and discharging of the at least one battery module (102a) and monitors a plurality of parameters associated with the at least one battery module (102a).
7. The arrangement (100) as claimed in claim 4, wherein the integrated bi-directional power converter (106) is configured to:
- convert DC power received from the at least one battery module (102a) into AC power; and
- convert AC power received from the line-frequency transformer into DC power, to charge the at least one battery module (102a).
8. The arrangement (100) as claimed in claim 4, wherein the integrated bi-directional power converter (106) comprises a DC link capacitor bank (112) connected with the battery management system (102b) to minimize voltage ripple between the battery management system (102b) and the integrated bi-directional power converter (106).
9. The arrangement (100) as claimed in claim 4, wherein the integrated bi-directional power converter (106) comprises a plurality of phase inverter legs (114a, 114b, 114c), wherein each of the phase inverter leg (114a, 114b, 114c) comprises a pair of switches (S1, S2), and wherein the pair of switches (S1, S2) of the plurality of phase inverter legs (114a, 114b, 114c) perform switching operation for three phase AC to DC conversion or vice versa.
10. The arrangement (100) as claimed in claim 4, wherein the switches (S1, S2) of two of the plurality of phase inverter legs (114a, 114b, 114c) perform switching operation for two phase AC to DC conversion or vice versa.