DESC:FIELD OF THE INVENTION
[0001] The field of present invention relates to batteries used in electric vehicles that needs to be recharged, and more particularly to a method of recharging in a user configurable charging time with high energy efficiency, as well as a device configured for use with such a method; of which the following is a specification, reference being had to the drawings accompanying and forming part of the same.

DESCRIPTION OF THE RELATED ART
[0002] Electric Vehicles have started penetrating the market for private and public transport across the globe which is seen as a potential solution for addressing environmental concerns. These vehicles use a battery as the energy source for powering the driving mechanism which normally has to be recharged at regular intervals. These batteries are normally charged using a charge equipment which could be present either in the vehicle or from a separate equipment which is not part of the vehicle that is connected to the vehicle during charging. The charging time of the charger depends on the power rating of the charger. Normally a high-power charger is used for fast charging and a low power charger is used for slow charging.
[0003] These chargers are built using power electronic converters and isolation transformers that exhibit maximum power efficiency when it is operated nearer to its rated power. Also, these chargers have a subsystem in the frontend that is connected to the electric utility which ensures that the charger doesn’t inject any undesirable harmonics into the electric utility system and thereby maintains power quality compliance as per mandatory regulations. These subsystems which is once again made of power electronic circuits achieves good power quality compliance nearly from 50 % of the rated conditions to the rated conditions. When the said subsystem is operating at less than 50 % of its rated condition, it doesn’t maintain power quality compliance. Also, the efficiency varies somewhere between 60 % to 90 % between 50 % to 100 % of load conditions.
[0004] Hence a high power fast charging equipment when used for a long duration charging, it operates at a power level much lesser than its rated power and hence will exhibit very poor electric efficiency as well as power quality compliance.
[0005] Even a low power slow charging equipment will exhibit maximum efficiency only when it is delivering its rated charge current (and hence rated power). However, the charging current doesn’t remain constant for the entire charging duration and comes down to as low as one tenth of the rated charging current. Hence the energy efficiency of the any charging equipment will be affected by the said phenomenon.
[0006] Normally, any battery cannot be always recharged at a fast duration, which is neither good for the battery nor the electric utility which will be subjected to high load demand. There will also be no requirement as such for the electric vehicle battery to be fast recharged at all the times.
[0007] For small passenger vehicles like e-auto and e-rickshaws which are capable of carrying a few number of passengers, are subjected to multiple trips within a city. The travel distance of these small passenger vehicles used by public in a single day, will be much higher when compared to a private electric vehicle user that is limited to a two-way trip in a week day. It would be desirable for these small passenger vehicles to have a long range of travel in one-night recharge. However, considering the size of the small passenger vehicle and its battery, the range of travel is limited in a single night recharge. Hence it would be desirable to have a fast recharging option in the middle of the day for these vehicles which caters to the public for commuting passengers.
[0008] It would be desirable and economical to have a single charge equipment for performing both full night slow charging and fast charging in the middle of a day at a reduced energy cost for each recharge. Currently a fast charging equipment would exhibit high efficiency only when it is operated at its rated conditions (and hence a poor efficiency at low power and high energy consumption), while a normal low power equipment cannot do a fast charging.
[0009] It would be also desirable to derive the power required for charging directly from renewable sources like Photovoltaic (PV) cells instead of extracting the power from PV using another storage devices and using it later to eliminate the losses in different conversion stages
[0010] Therefore, what is needed is a method and device to carry out the recharge at a user desirable speed and also achieve high efficiency throughout the duration of the charging and hence reduce the energy cost of each and every recharge as well as capable of performing the charging either from an electric utility supply or an PV array
BRIEF DESCRIPTION OF THE INVENTION
[0011] In view of the foregoing considerations, it is desirable to provide a device and method to
perform the recharge of batteries used in electric vehicle that is capable of doing the charging at a user desirable speed and exhibit maximum energy efficiency at all charging speeds
[0012] FIG 1 shows the charging current and the efficiency of charging in the conventional method of charging
[0013] In accordance with an aspect of the invention, the problem of reduction of efficiency of a charger within the entire charging duration is solved by using multiple number of modular charger subsystem of lower power rating and operating only those modular charger subsystems that is just required at the given moment of charging based on the charging current.
[0014] FIG.2 is a block diagram illustrating the proposed energy efficient modular charger (EEMC) concept. FIG 2 shows a EEMC 200, which comprises of three power stages and a power control unit (PCU) 200e. The front-end power stage 200a consists of uncontrolled rectifier with necessary protection circuits, followed by a dc-dc converter stage 200b. Finally, the last stage 200c is the one in which the charging algorithm is implemented, is connected to the battery through necessary sensor and protection circuits 200d.
[0015] In one embodiment, the proposed EEMC is connected to either a single phase or three phase AC supply, the second power stage 200b acts as a power factor control and input current wave shaping circuit.
[0016] In another embodiment, the proposed EEMC is connected to a PV (photo voltaic) solar panel, then the second power stage 200b acts as a maximum power point tracking controller for the PV input
[0017] Other features and advantages of the disclosure will become apparent by reference to the following description taken in connection with the accompanying drawings.
[0018] The above brief summary sets forth rather broadly the more important features of the present invention in order that the detailed description thereof that follows may be better understood, and in order that the present contributions to the art may be better appreciated. In this respect, before explaining several embodiments of the invention in detail, it will be understood that the invention is not limited in its application to the details of the construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood, that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.
[0019] As such, those skilled in the art will appreciate that the conception, upon which disclosure is based, may readily be utilized as a basis for designing other structures, methods, and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS
[0020] A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate a presently preferred embodiment of the invention, in which:
[0021] FIG. 1 shows a normal recharging profile of a battery and the efficiency of the charger obtained from a conventional charger and the proposed EEMC charger
[0022] FIG. 2 illustrates the block diagram representation of an embodiment of the present invention
[0023] FIG. 3 illustrates the charging current and efficiency over the period of charging time of the proposed EEMC charger
[0024] FIG. 4 describes the control method of dc-dc converter in power factor correction mode
[0025] FIG. 5 shows the flow chart for control of dc-dc converter in Maximum Power Point Tracking (MPPT) mode
[0026] FIG. 6 shows the flow chart for charging algorithm of the Modular charger subsystem
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] As used herein, an element or function recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or functions, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the claimed invention should not be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.
[0028] Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, one of the embodiments of the present invention will now be described.
[0029] Fig.1 shows the efficiency of conventional chargers as a function of the rated charging current. It cab be observed the efficiency remains maximum at the rated current, but reduces for current less than its rated current.
[0030] Fig. 2 is a block diagram of an exemplary way of recharging a battery of an embodiment of the present invention using the proposed EEMC 200.
[0031] Fig. 3 shows the efficiency of the proposed EEMC, which is exhibits a maximum efficiency for all values of charging current from its rated value till a small fraction of its rated value.
[0032] Referring back to FIG. 2 the front-end subsystem 200a receives input either from a single phase or three phase AC supply and also has a third option of connecting it to an Photo Voltaic (PV) array. The subsystem 200a comprises of rectifier and EMI filters when connected to a single phase or three phase AC supply, provides a rectified DC output voltage as the input to the subsequent stage 200b.
[0033] The same subsystem 200a when connected to a PV array input simply acts as a reverse polarity protection circuit and the two leads from the PV array could be connected in either way
[0034] The subsystem 200b receives an unfiltered DC output from the 200a when it is connected to a single phase or three phase AC supply. 200b comprises of dc-dc converter, which plays a dual role, one it provides a regulated and filtered DC output voltage to the subsequent stage 200c, and also it ensures the rectifier stage 200a draws a sinusoidal current that is in-phase with the supply voltage.
[0035] The subsystem 200b ensures the EEMC connected to the utility supply (single or three phase) operates at unity power factor and less than 5% Total Harmonic Distortion (THD) in current. The subsystem 200b which comprises a dc-dc converter receives the gate pulses from the power control unit (PCU) 200e that implements a control algorithm to maintain power factor and THD within its prescribed limits. The output of the subsystem 200b is connected to the input of the subsequent modular charger stage 200c.
[0036] The same subsystem 200b comprising of a dc-dc boost converter operates as a Maximum Power Point Tracking (MPPT) controller when the EEMC is connected to an PV array input. The PCU 200e senses the PV voltage and current and generates a different set of (Pulse Width Modulated) PWM pulses in-order to ensure MPPT tracking of PV array. Now the output of the subsystem 200b is an unregulated but filtered DC voltage, which is given as the input to the subsequent stage 200c.
[0037] The modular charger stage 200c comprises of ‘m’ x ‘n’ modular chargers with ‘m’ number of strings connected in parallel and each string consists of ‘n’ number of modular chargers connected in series. Each string of the total ‘m’ strings delivers a fraction of the total charging current delivered by the EEMC. Similarly, each modular charger connected in series in a string carries a fraction of the total charger voltage of the EEMC.
[0038] Each modular charger in the 200c comprises of an isolated dc-dc converter rated at a power which is equal to small fraction of the total rated power of the EEMC charger. Also, each modular charger is controlled individually by a PWM control signal provided by the power control unit 200e.
[0039] The output of the modular charger subsystem 200c is connected to the output of the EEMC which in turn is connected to the battery through a sensor and protection subsystem 200d.
[0040] The subsystem 200d comprises of voltage and current sensors for sensing the EEMC charger voltage and current. It also comprises of temperature sensors mounted at crucial point of the chargers. All the sensor output signals are connected as an input to the power control unit 200e. Apart from sensors 200d also comprises of protection circuit for over current, over voltage, reverse polarity protection etc.
[0041] Referring still to Fig. 2, the power control unit (PCU) 200e is the main control unit of the EEMC that monitors and controls all the subsystems 200a, 200b, 200c and 200d of EEMC. The PCU 200e comprises of microcontroller, electronic interfacing circuits and also a communication interface circuit to communicate with an Mobile Application.
[0042] The charging algorithm is implemented in the microcontroller of the PCU 200e, which generates the PWM pulses required for the modular chargers in 200c as well as the dc-dc converters in the subsystem 200b and these pulses are given through the electronic interfacing circuits. The PWM pulses are generated based on the current and voltage sensor signals of the subsystem 200d.
[0043] The power factor correction (PFC) algorithm as well as the MPPT algorithm is also implemented in the microcontroller of PCU 200e. The appropriate algorithm is chosen based on the input of the EEMC. PFC control algorithm is chosen for 200b if the input of the EEMC is single phase or three phase utility supply and the MPPT control algorithm is chosen if the input of the EEMC is connected to an PV array input.
[0044] FIG. 4 shows the control block diagram of the PFC algorithm implemented by PCU 200e. The output voltage of the dc-dc converter stage 200b is sensed and compared with a reference voltage and the error voltage is processed by a Proportional-Integral (PID) controller and generates a current reference. This reference current is compared with the actual current of dc-dc converter and the error is processed by another PID controller. The output of this second PID controller is compared with a carrier waveform and PWM pulses are generated, which is given to the power semiconductor device of the dc-dc converter of stage 200b
[0045] FIG. 5 shows the control flow chart of the MPPT algorithm implemented by PCU 200e when the EEMC is connected to an PV array input. The MPPT algorithm is based on the classical perturb and observe (P&O) algorithm. In this method, the PV voltage and current is sensed at periodical intervals and the PV power is calculated. Now the duty cycle of the PWM pulse is slightly altered and once again the new value of PV voltage and power is calculated. Based on the delta change in PV voltage and power the new value of the duty cycle for the PWM pulse is chosen as shown in FIG. 5
[0046] The PCU 200e having a communication interface with a mobile application enables the user to monitor as well as control the charging. The user could start and stop the charging from the mobile application and also monitor the status of the charging.
[0047] FIG. 6 shows the charging algorithm implemented by the PCU 200e for the modular charger stage 200c. The PCU 200e generates ‘m’ x ‘n’ no of PWM pulses for the ‘m’ x ‘n’ isolated dc-dc converters of the modular charger stage 200c. PCU 200e interacts with the user by an mobile application and performs the charging. The charging is done based on constant current (CC) followed by constant voltage (CV) method. Appropriate charging profile is chosen by the PCU for lead acid and lithium ion battery. The information about the battery type and rating is given to the PCU 200e from the mobile application by the user. The PCU also performs a battery diagnostic and ascertain the health of the battery, its current state of charge (SOC) before initiating the charging.
[0048] The PCU 200e continuously monitors the signals from the protection circuits and shut downs the charge at any point of time during charging in case if there is an error. The current SOC of the battery is continuously updated to the user during charging.
[0049] Referring to FIG. 2, the embodiments have been described generally by employing an dc-dc converter topology for the second stage 200b and isolated dc-dc converter for third stage 200c. It will be seen that the embodiments are not so limited and are equally useful with various other topologies of power electronic interfaces between the EUT and the electrical utility grid.
[0050] In addition, while the present invention has been shown in the drawings and fully described above with particularity and detail in connection with what is presently deemed to be practical and several of the preferred embodiments of the invention, it will be apparent to those of ordinary skill in the art that many modifications thereof may be made without departing from the principles and concepts set forth herein. Hence, the proper scope of the present invention should be determined only by the broadest interpretation of the appended claims so as to encompass all such modifications and equivalents.
[0051] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
,CLAIMS:What is claimed is
1. A method for charging different types of batteries used in electric vehicles (EV) using the same hardware circuit, at high energy efficiency without any active cooling arrangement, that can be used for both fast charging as well as slow charging but still maintaining high efficiency for all speed of charging and all values of charging current from its rated value to a fraction of its rated value, the method comprising of
a. using multiple number of modular power factor control circuits (MPFC) that are connected in parallel and each modular PFC has a control input that forms the stage-1
b. using multiple number of modular chargers (MC) that are connected in series and parallel connected to the output of stage-1 and forms the stage-2 and each MC has a control input
c. using a power control unit (PCU) capable of communicating with electric vehicle as well as the user through multiple communication means, also capable of providing control signals to control the magnitude of current and voltage of individual MC of stage-2 as well as providing the control signals for each MPFC of stage-1, so that the individual MPFC, MC and hence the overall charging system operates at maximum efficiency
2. The method of claim 1, wherein said PCU is capable of communicating with the battery management system (BMS) of electric vehicle, performs a battery diagnostic to identify the health of the battery and state of charge (SOC) of the battery
3. The method of claim 1, wherein said PCU is also capable of communicating with the user and reads the charging time requirement and battery information including its type, voltage and capacity ratings
4. The method of claim 1, wherein said PCU decides the charging profile required to complete the charge in user defined time and subsequently energizes part of the MPFC and MC of stage-1 and stage-2 respectively, based on the charging current and voltage requirement, so that the energized MPFC and MC of stage-1 and stage-2 operates at maximum efficiency
5. The method of claim 1, wherein said stage-1 is capable of operating with an AC supply from electric utility or an DC input from an PV array and the PCU operates the same MPFC of stage-1 in maximum power point tracking (MPPT) mode if the said stage 1 is connected to PV array, in-order to extract maximum power from the PV array at any point of time in a day
6. The method of claim 1, wherein said PCU provides the control signals to the MPFC of stage-1 so that the power factor is maintained at unity magnitude and harmonic compliance is achieved, if the stage-1 is connected to an electric utility AC supply
7. A single apparatus for charging different types of batteries used in electric vehicles (EV), at high energy efficiency without any active cooling arrangement, that can be used for both fast charging as well as slow charging but still maintaining high efficiency for all speed of charging and all values of charging current from its rated value to a fraction of its rated value, said apparatus comprising of
a. multiple number of controllable power electronic dc-dc converter circuits (DDC) of power rating fractional of the said apparatus rating, connected in parallel and forms the power stage-1 (PS1), with each DDC having a control input
b. multiple number of controllable isolated dc-dc converter (IDDC) of voltage and current rating fractional of the said apparatus voltage and current rating respectively, that are connected in series and parallel configuration and forms power stage-2 (PS2), with each IDDC having a control input
c. a power control unit (PCU) configured to
i. control all the individual DDC and IDDC of said stages PS1 and PS2 respectively
ii. communicate with the user through a mobile phone application
iii. communicate with the EV through any one of the multiple communication interfaces
8. The apparatus of claim 7, wherein said PCU comprises of microcontroller, electronic interfacing circuits, provides output control signals to all IDDC of PS2 and all DDC of PS1 and communication interface circuits that includes Controller area network (CAN) port to communicate with the EV and Bluetooth as well as Wireless Fidility (Wi-Fi) option to communicate with the user
9. The said microcontroller of claim 8 is preloaded with software program that selects the appropriate charging profiles based on the information received from user and EV