WO2022064268A1

WO2022064268A1 - System and method for unity power factor based battery charger and discharger

Info

Publication number: WO2022064268A1
Application number: PCT/IB2020/060749
Authority: WO
Inventors: Jayanand B; Jayan C B
Original assignee: Jayanand B; Jayan C B
Priority date: 2020-09-28
Filing date: 2020-11-16
Publication date: 2022-03-31

Abstract

A system and method for unity power factor based battery charger and discharger is disclosed. The system includes a three phase transformer to provide isolation between battery and grid, where the grid provides three phase input supply. The system includes a boost rectifier including an IGBT based bridge rectifier to provide AC voltage to DC voltage conversion of the three phase input supply with power factor correction. The system includes an interleaved buck/boost converter to adjust the output voltage based on the DC voltage sensed by the boost rectifier to control a charging current of the battery. The charger/discharger results in close to unity power factor. The system uses synchronous rotating frame based (D-Q) algorithm which is one of the active power filter technique for harmonic mitigation and power factor correction and result in current ripple reduction.

Description

SYSTEM AND METHOD FOR UNITY POWER FACTOR BASED BATTERY CHARGER AND DISCHARGER

This International Application claims priority from a Patent application filed in India having Patent Application No. 202041042078, filed on September 28, 2020, and titled “SYSTEM AND METHOD FOR UNITY POWER FACTOR BASED BATTERY CHARGER AND DISCHARGER”.

FIELD OF INVENTION

Embodiments of the present disclosure relate to charging and discharging system for vehicles and more particularly to a system and method for unity power factor based battery charger and discharger.

BACKGROUND

As an important measurement to reduce carbon emission, electrification of transportation system is an irreversible developing trend in modern society. Battery technologies and related charging methods are key to promote the electric vehicle in the market. With more and more grid-tied battery chargers put in operation, pollution to the AC grid system should be depressed as much as possible through power factor correction. The power factor is defined as “the ratio of the real power flowing to the load to the apparent power in the circuit. An AC system with a lower power factor draws more current than a system with a higher power factor when a same amount of power is transferred. Generally, the power factor is desired to be 1 for any grid-tied AC system.

For battery charging, any ac to de converter circuit may be used. In order to get perfect power factor correction at the ac source, a converter using self-controlled power electronic switch is used. However, such power factor controlled converter is a boost converter so that only voltages higher than the peak value of the input voltage are available as the DC output. In order to match this voltage with the voltage of a battery, buck/boost converters are used. However, ordinary buck/boost converter has two drawbacks of more ripple content in the DC output voltage for a given value of filter capacitance and the boost converters are unidirectional, another circuit is needed for discharging the battery into grid at unity power factor.

Hence, there is a need for an improved system and method for unity power factor based battery charger and discharger to address the aforementioned issue(s).

BRIEF DESCRIPTION

In accordance with an embodiment of the present disclosure, a system for unity power factor based battery charger and discharger is provided. The system includes a dual mode subsystem configured to operate in a charging mode and a discharging mode. The dual mode subsystem in the charging mode includes an input transformer configured to provide isolation between battery and grid, where the grid provides three phase input supply though an incoming fuse. The dual mode subsystem in charging mode also includes a boost rectifier comprising a line choke and an insulated gate bipolar transistor (IGBT) based bridge converter. The boost rectifier is configured to provide AC voltage to DC voltage conversion of the three phase input supply with power factor correction. The power factor correction is obtained by a PI controller configured to obtain a voltage error by sensing the DC voltage and compare the DC voltage with a predetermined DC voltage. The PI controller is also configured to produce a first reference current based on obtained voltage error. The power factor correction is further obtained by a phase lock loop control system configured to multiply the reference current obtained through the PI controller with at least three unity magnitude sinewaves generated using the three phase input supply to obtain a multiplied output. The phased lock loop control system is also configured to produce a second reference current for a current controller based on the multiplied output to obtain a unity power factor. The dual mode subsystem in charging mode further includes an interleaved buck/boost converter coupled to the boost rectifier. The interleaved buck boost converter is configured to multiply switching frequency by a predefined factor to half a ripple content and EMI filtering requirements for the capacitors and inductors thereby reducing the ripple content in the voltage fed to the battery. The interleaved buck/boost converter is also configured to adjust the voltage based on the DC voltage sensed by the boost rectifier to control a charging current of the battery. The dual mode subsystem in the discharging mode includes the interleaved buck/boost converter configured to boost the output voltage of the battery to a voltage required at the boost rectifier. The boost rectifier act as an inverter and configured to feed back the charge from the battery into the grid at unity power factor obtained in the charging mode by converting the DC voltage into AC voltage via IGBT based bridge converter.

In accordance with another embodiment of the present disclosure, a method for unity power factor based battery charger and discharger is provided. The method includes providing, by an input transformer, isolation between battery and grid, wherein the grid provides three phase input supply though an incoming fuse. The method also includes providing, by a boost rectifier comprising a line choke and an IGBT based bridge converter, AC voltage to DC voltage conversion of the three phase input supply with power factor correction, wherein the power factor correction is obtained, by a PI controller, a voltage error by sensing the DC voltage and compare the DC voltage with a predetermined DC voltage. The power factor correction further includes producing, by the PI controller, a first reference current based on obtained voltage error. The power factor correction further includes multiplying, by a phase lock loop control system, the reference current obtained through the PI controller with at least three unity magnitude sinewaves generated using the three phase input supply to obtain a multiplied output. The power factor correction further includes producing, by the phase lock loop control system, a second reference current for a current controller based on the multiplied output to obtain a unity power factor. The method further includes multiplying, by an interleaved buck/boost converter, switching frequency by a predefined factor to half a ripple content and EMI filtering requirements for the capacitors and inductors thereby reducing the ripple content of voltage fed to the battery. The method further includes adjusting, by the interleaved buck/boost converter, the voltage based on the DC voltage sensed by the boost rectifier to control a charging current of the battery. The method further includes boosting, by the interleaved buck/boost converter, the output voltage of the battery to a voltage required at the boost rectifier in discharging mode. The method further includes feeding, by the boost rectifier, the charge from the battery into the grid at unity power factor obtained in the charging mode by converting the DC voltage into AC voltage via the IGBT based bridge converter in discharging mode.

To further clarify the advantages and features of the present disclosure, a more particular description of the disclosure will follow by reference to specific embodiments thereof, which are illustrated in the appended figures. It is to be appreciated that these figures depict only typical embodiments of the disclosure and are therefore not to be considered limiting in scope. The disclosure will be described and explained with additional specificity and detail with the appended figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be described and explained with additional specificity and detail with the accompanying figures in which:

FIG. 1 is a block diagram representation of system for unity power factor based battery charger and discharger in accordance with an embodiment of the present disclosure;

FIG. 2 is a detailed block diagram representation of system of FIG. 1 , depicting one embodiment of the system in accordance with an embodiment of the present disclosure;

FIG. 3 is a schematic representation of input transformer of system of FIG. 1 in accordance with an embodiment of the present disclosure;

FIG. 4(a) shows the IGBT based bridge converter of system of FIG. 1 in accordance with an embodiment of the present disclosure;

FIG. 4(b) shows three phase PLL of system of FIG. 1 in accordance with an embodiment of the present disclosure; FIG. 4 (c) depicts the block diagram of the control scheme of the boost rectifier in accordance with an embodiment of the present disclosure;

FIG. 5(a) and 5(b) is a block diagram representation of the interleaved buck/boost converter of system of FIG. 1 in accordance with an embodiment of the present disclosure;

FIG. 5(c) depicts the block diagram of the control scheme of the interleaved buck/boost converter in accordance with an embodiment of the present disclosure;

FIG. 6 is a schematic representation of digital signal processing (DSP) controller of FIG. 2 in accordance with an embodiment of the present disclosure;

FIG. 7 is a graphical representation of results from charger and discharger of FIG. 1 in FIGs. 7(a) -7(f) in accordance with an embodiment of the present disclosure; and

FIG. 8(a) and 8(b) is a flow chart representing the steps involved in a method for unity power factor based charger and discharger in accordance with an embodiment of the present disclosure.

Further, those skilled in the art will appreciate that elements in the figures are illustrated for simplicity and may not have necessarily been drawn to scale. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the figures by conventional symbols, and the figures may show only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the figures with details that will be readily apparent to those skilled in the art having the 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 figures and specific language will be used to describe them. 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 would normally occur to those skilled in the art are to be construed as being within the scope of the present disclosure.

The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such a process or method. Similarly, one or more devices or sub-systems or elements or structures or components preceded by "comprises... a" does not, without more constraints, preclude the existence of other devices, sub-systems, elements, structures, components, additional devices, additional sub-systems, additional elements, additional structures or additional components. Appearances of the phrase "in an embodiment", "in another embodiment" and similar language throughout this specification may, but not necessarily do, all refer to the same embodiment.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this disclosure belongs. The system, methods, and examples provided herein are only illustrative and not intended to be limiting.

In the following specification and the claims, reference will be made to a number of terms, which shall be defined to have the following meanings. The singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise.

Embodiments of the present disclosure relate to system and method for unity power factor based battery charger and discharger. The system includes a dual mode subsystem configured to operate in a charging mode and a discharging mode. The dual mode subsystem in the charging mode includes an input transformer configured to provide isolation between battery and grid, where the grid provides three phase input supply though an incoming fuse. The dual mode subsystem in charging mode also includes a boost rectifier comprising a line choke and an insulated gate bipolar transistor (IGBT) based bridge converter. The boost rectifier is configured to provide AC voltage to DC voltage conversion of the three phase input supply with power factor correction. The power factor correction is obtained by a PI controller configured to obtain a voltage error by sensing the DC voltage and compare the DC voltage with a predetermined DC voltage. The PI controller is also configured to produce a first reference current based on obtained voltage error. The power factor correction is further obtained by a phase lock loop control system configured to multiply the reference current obtained through the PI controller with at least three unity magnitude sinewaves generated using the three phase input supply to obtain a multiplied output. The phased lock loop control system is also configured to produce a second reference current for a current controller based on the multiplied output to obtain a unity power factor. The dual mode subsystem in charging mode further includes an interleaved buck/boost converter coupled to the boost rectifier. The interleaved buck boost converter is configured to multiply switching frequency by a predefined factor to half a ripple content and EMI filtering requirements for the capacitors and inductors thereby reducing the ripple content of voltage fed to the battery. The interleaved buck/boost converter is also configured to adjust the output voltage based on the DC voltage sensed by the boost rectifier to control a charging current of the battery. The dual mode subsystem in the discharging mode includes the interleaved buck/boost converter configured to boost the output voltage of the battery to a voltage required at the boost rectifier. The boost rectifier act as an inverter and configured to feed back the charge from the battery into the grid at unity power factor obtained in the charging mode by converting the DC voltage into AC voltage via IGBT based bridge converter.

FIG. 1 is a block diagram representation of system (10) for unity power factor based battery charger and discharger in accordance with an embodiment of the present disclosure. The system (10) includes a dual mode subsystem (20) configured to operate in a charging mode and a discharging mode. The dual mode subsystem (20) is connected to three phase supply (30) through incoming fuse (40). The subsystem further includes an input transformer (50) used in the charger provides isolation between battery side and grid side. Both charging and discharging operation may be considered as combination of two power electronic stages. In charging mode, the first stage includes a boost rectifier (60) comprising a line choke and an insulated gate bipolar transistor (IGBT) based bridge converter (70) which is configured to convert AC voltage to DC voltage. The second stage includes an interleaved buck/boost converter (80) configured to convert DC voltage to battery voltage. The direction of power flow under charging mode is from grid to battery (90) via output fuse (95). In discharging mode, the energy available in the battery is fed back to the utility grid. The direction of power flow is from battery to grid. The first stage includes DC-DC conversion and the second stage is DC-AC conversion. In this mode three phase IGBT converter works as inverter.

FIG. 2 is a detailed block diagram representation of system (10) of FIG. 1, depicting one embodiment of the system in accordance with an embodiment of the present disclosure. The system (10) includes 3 phase input transformer (50), line choke (100), three phase IGBT based bridge converter (70), DC/DC converter (interleaved buck/boost converter) (80), DSP controller (110) and gate drive circuits (120). During the charging mode, the input transformer is working as a step down transformer (415V to 80V). The transformer secondary winding is connected to the three phase line chokes which may be also being called as line filter. The line choke is then connected to the three phase IGBT bridge converter. The line choke and the IGBT based bridge converter may be called as boost rectifier, as the boost rectifier converts 80 V AC into 165 V DC and maintain 165 V DC. Also, the boost rectifier maintains close to unity power factor. The next stage contains a DC -DC converter which is the interleaved buck boost converter, which convert 165 V DC into battery voltage and hence in charging mode, this stage may be considered as a buck stage. Output of this stage is connected to battery terminal. In discharge mode, the battery (90) is connected to DC -DC converter which converts battery voltage into 165 V DC link and hence in this mode DC-DC converter may be called as a boost converter. Further, the DC link voltage is converted to AC voltage by 3 phase IGBT based bridge converter. Output from 3 phase IGBT based bridge converter is connected to the secondary winding of transformer through a line choke. Furthermore, the gate drive circuitry (120) needs to be isolated from the control circuit to provide level shifting and improve noise immunity and safety. By using the optocoupler, the input signal and the module are isolated from each other. The isolated gate driver is required for driving the top switch of the half-bridge module as the gate voltage has to be applied with respect to the switch node terminal. Isolation is also required to electrically separate the low-voltage operator side from the high-voltage drive side to meet safety requirements.

The dual mode subsystem (20) includes a digital signal processing controller (110) configured to control operations of the input transformer, the boost rectifier and the interleaved buck/boost converter. The digital signal processing controller (110) is also configured to scale and convert battery voltage, battery current and DC link voltages to digital signals. The digital signal processing controller (110) is further configured to control the width of pulses applied to a gate terminal of IGBT and thereby control the output voltage and phase of the input current. In one embodiment, the digital signal processing controller (110) is configured to measure temperature of one or more heat sink mounted on each IGBT via one or more temperature sensors to avoid breakdown of the battery charger and discharger. One embodiment of the input transformer, the IGBT based bridge converter, the interleaved buck/boost converter and the DSP controller are described in detail in FIG. 3, FIG. 4, FIG. 5 and FIG. 6 respectively.

FIG. 3 is a schematic representation of input transformer (50) of system of FIG. 1 in accordance with an embodiment of the present disclosure. The input transformer (50) is used in the charger provides isolation from utility grid and also step down the three phase voltage to required value for IGBT boost rectifier. Since the rectifier unit work as boost rectifier, the peak ac output voltage of the transformer secondary is to be less than the de link voltage. In a specific embodiment, the input transformer may include lOkVA, 3 wires, 415V/ 80V 50Hz specification.

FIG. 4 is a block diagram representation of IGBT based bridge converter (70) of system of FIG. 1 in accordance with an embodiment of the present disclosure. FIG. 4(a) shows the IGBT based bridge converter which is a three phase converter and includes input inductor (L), six IGBT switches (T1 ~T6), DC link capacitor (C2). The converter includes inductors (130) at input side and hence provide continuous input current. The IGBT based bridge converter includes two modes mode 1 and mode 2. In mode 1, When the switch T2 is closed (ON) and it is conducting as a short circuit through inductors connected across R phase and B or Y phase (30) (since freewheeling diode across T6 or T4 is forward biased). In this mode, the current through R phase rises. At the same time the voltage of C2 (140) reverse biases diode across T1 and turn it off. The capacitor C2 discharges its energy to the load circuit. In mode 2, When the switch T2 is open (OFF), the diode (Tl) is forward biased and directing energy to the output. The capacitor will start to charge from input supply (voltage across R phase and B or Y phase) and the energy stored in the inductor transferred to the load. The capacitor C2 is the medium for transferring energy from source to load.

The pulses to the switches ( 150) are controlled by sine PWM obtained from the digital signal controller. Sine PWM is employed in such a way that the converter draws only current which is in phase with voltage. FIG. 4(b) shows three phase PLL (160) where to control the sinusoidal input current, it is advantageous to transform the dynamic variables into the synchronous reference frame (dq). Synchronous reference frame control uses a reference frame transformation module (abc — dq), called Park transformation to transform the grid current and voltage waveforms into a reference frame that rotates synchronously with the grid voltage. After the park transformation, the control variables become DC quantities instead of sinusoids of a given frequency. These DC quantities are used in control scheme. In case of grid connected converter, frequency of the converter output should be same as frequency of the grid voltage. To estimate the phase angle, open loop and closed loop methods are available. The closed loop methods are commonly known as Phase-Locked Loops or PLLs. The advantages of a PLL are speed of response to phase, frequency and voltage amplitude disturbances, harmonic rejection and line unbalance in the case of three-phase systems. As used herein, the phase-locked loop is a control system that generates an output signal whose phase is related to the phase of an input reference signal. FIG. 4 (c) depicts the block diagram of the control scheme (170) of the boost rectifier. The control scheme uses direct and quadrature axis components of voltage and current. The control scheme for each mode differs only in reference current Id (171) generation. In charging mode, reference DC link voltage and actual DC link voltage are compared. The error of these voltages is given to the PI controller (172) to generate Id reference. In discharging mode, the reference battery current and actual battery current are compared. The error of these current is given to a PI controller to generate Id reference. This Id reference is then compared with actual Id derived from the d-q transformation of input currents and the error is given to a PI controller. For unity power factor operation, the Iq reference is set at zero which is then compared with actual Iq and the error is given to another PI controller. The outputs of PI controllers are then processed, and the pulses are generated using sine PWM generator (173) as shown in the control scheme.

FIG. 5(a) and 5(b) is a block diagram representation of the interleaved buck/boost converter (80) of system of FIG. 1 in accordance with an embodiment of the present disclosure. The multiphase buck converter (81) includes two buck converters in parallel. When two or more synchronous buck converters are put in parallel, they may form a multiphase converter. To be called a multiphase converter, each buck has a switching control signal with phase difference of 3607N where N is the phase number. In case of the two phases, each phase control signal is shifted from each other by 180°. In case of four phases, control signal for each phase is shifted from each other by 90° degrees and so on. The switch T1 (82) and anti-parallel diode in switch T2 (83) form one phase and switch T3 (84) and anti-parallel diode in switch T4 (85) form second phase of a two phase interleaved boost converter. The multiphase converter combines all phase shifted inductor currents from individual channel or phase, and therefore greatly reduces the total current ripple flowing into the output capacitor. With the current ripple reduction, the output voltage ripples are also greatly reduced which enables the use of very small inductances in each phase to improve the transient response requirement. The reduced output ripple voltage in turn allows for more room for voltage variations during load transient because the ripple voltage will consume a smaller portion of the total voltage tolerance budget. Consequently, multi phasing helps to improve the load transient performance and minimize the output capacitance. As shown in FIG. 5(b), the interleaved boost converter (86) comprises two boost converters in parallel. Here the switch T2 and antiparallel diode across switch T1 forms one phase, the switch T4 and antiparallel diode across switch T3 forms the second phase of a inter leaved boost converter.

FIG. 5(c) depicts the block diagram of the control scheme (180) of the interleaved buck/boost converter. The interleaved buck converter converts 165V de link voltages into the battery voltage. In the control scheme for the interleaved buck converter, actual battery voltage is sensed which is then compared with reference battery voltage to generate error voltage. This error voltage is given as an input to the PI controller (172). Output of this PI controller is a current reference. This reference signal is compared with actual battery current to generate error current. This error current is given to another PI controller which will give the control signal for PWM generation block (173). This block will produce two pulses stream having 180° phase difference. These pulses are used to drive the switches T1 and T3. In this mode, switches T2 and T4 are turned off. The interleaved boost converter converts the battery voltage in to 165V de link. In the control scheme for the interleaved boost converter, the actual de link voltage is compared with a reference de link voltage and the error voltage is given to a PI controller. Output of this PI controller is a control signal for a PWM generation block. This block will produce two pulses stream having 180° phase difference. These pulses are used to drive the switches T2 and T4. In this mode, switches T1 and T3 are turned off.

FIG. 6 is a schematic representation of digital signal processing (DSP) controller (110) of FIG. 2 in accordance with an embodiment of the present disclosure. The digital signal controller (110) continuously measures the input parameters, and then processes the measured parameters to get satisfactory operation of the charger. The DSP controller (110) controls the width of pulses applied to the gate terminal of IGBT and thereby control the output voltage and phase of the input current. Therefore, total number of ADC channels required is 14 channels. Similarly, there are five IGBT half bridge modules; hence ten PWM channels are required for controlling IGBT modules. Also, controller includes additional 20nos of general purpose pins for alarms and indications. The charger/ discharger has six different modes. The general purpose pins (GPIO pins) (113) of the DSP controller are used to select modes. These pins are connected to mode selection switches through encoder IC. The encoder IC gives unique output corresponds to selector switch position. Data inputs and outputs are active at the low logic level. Various modes and encoder outputs and decoder outputs are shown in below table 1 and table 2 respectively. In one embodiment, the six different modes are indicated using LED.

Table 1

Table 2

The control signals for both modes of operation are generated in DSP controller. Input AC voltages, AC currents, DC link voltage, Battery voltage and Battery current are sensed and given to the DSP controller board. There, these signals are conditioned and are given as analog inputs to the ADC pins of the DSP. Programs are written to the DSP controller. The DSP controller generates the switching signals for three phase IGBT bridge converter and interleaved buck/boost converter. These signals are given to the IGBT gate driver circuits to trigger corresponding IGBTs. In one embodiment, the digital signal processing controller is configured to measure temperature of one or more heat sink mounted on each IGBT via one or more temperature sensors (112) to avoid breakdown of the battery charger and discharger. FIG. 7 is a graphical representation of results (190) from charger and discharger of FIG. 1 in accordance with an embodiment of the present disclosure. FIG. 7(a) and FIG. 7(b) shows R phase input voltage (191) and input current (192) waveforms for charging mode and discharging mode respectively. For charging mode, voltage and current waveforms are in phase, such that the power flows in forward direction. For discharging mode, voltage and current waveforms are in out of phase, such that the power flows in reverse direction. In both cases, displacement power factor is almost unity. FIG. 7(a) shows input current of 5.7 A RMS for a battery current of 30A DC. FIG. 7(b) shows input current (193) of 5.8A RMS for a battery current of 40A DC. FIG. 7(c) shows the battery voltage (194) in charging mode. Figure shows the output voltage in boost mode. Output voltage has very small ripple voltage and it is maintained almost constant. FIG. 7(d) and FIG. 7(e) show the battery current during charging (195) and discharging (196) respectively. FIG. 7(f) shows the efficiency curves (197) for charging and discharging. The efficiency of IGBT based battery charger nearly equal to conventional SCR based battery chargers. Battery charger has an efficiency of 88%.

FIG. 8(a) and 8(b) is a flow chart representing the steps involved in a method (200) for unity power factor based charger and discharger in accordance with an embodiment of the present disclosure. The method (200) includes providing, by an input transformer, isolation between battery and grid, wherein the grid provides three phase input supply though an incoming fuse in step 210. In one embodiment, the charging mode comprises a power flow from the grid to the battery and the discharging mode comprises the power flow from the battery to the grid. The method (200) also includes providing, by a boost rectifier comprising a line choke and an IGBT based bridge converter, AC voltage to DC voltage conversion of the three phase input supply with power factor correction in step 220. In a specific embodiment, the IGBT based bridge converter comprises at least six IGBT switches, a DC link capacitor and an input inductor to provide continuous input current, wherein the at least six IGBT switches are configured to control pulses by a sine PWM obtained from the digital signal controller. The power factor correction is obtained by obtaining, by a PI controller, a voltage error by sensing the DC voltage and compare the DC voltage with a predetermined DC voltage in step 230. The power factor correction further includes producing, by the PI controller, a first reference current based on obtained voltage error in step 240. The power factor correction further includes multiplying, by a phase lock loop control system, the reference current obtained through the PI controller with at least three unity magnitude sinewaves generated using the three phase input supply to obtain a multiplied output in step 250. The power factor correction further includes producing, by the phase lock loop control system, a second reference current for a current controller based on the multiplied output to obtain a unity power factor in step 260.

The method (200) further includes multiplying, by an interleaved buck/boost converter, switching frequency by a predefined factor to half a ripple content and EMI filtering requirements for the capacitors and inductors thereby reducing the ripple content of an output voltage of the battery in step 270. The method (200) further includes adjusting, by the interleaved buck/boost converter, the output voltage based on the DC voltage sensed by the boost rectifier to control a charging current of the battery in step 280. In some embodiments, the interleaved buck/boost converter having a multiphase buck converter comprises at least two buck converters in parallel, wherein each of the at least two buck converters include a switching control signal with phase difference of 360o /N, N is phase number. In such an embodiment, the multiphase buck converter is configured to combine a plurality of phase shifted inductor currents from individual channel and reduce the total current ripple flowing into an output capacitor.

The method (200) further includes boosting, by the interleaved buck/boost converter, the output voltage of the battery to a voltage required at the boost rectifier in discharging mode in step 290. The method (200) further includes feeding, by the boost rectifier, the charge from the battery into the grid at unity power factor obtained in the charging mode by converting the DC voltage into AC voltage via the IGBT based bridge converter in discharging mode in step 300. V arious embodiments of the system and method for unity power factor based battery charger and discharger as described above enables an IGBT based 110V/ 70A unity power factor battery charger/ discharger in which the line current has lower total harmonic distortion compared to conventional SCR based chargers. The dq theory of three phase to two phase transformation is used which improves the power factor and reduces the input current harmonics in the converter. The synchronous reference frame (D-Q) model based control scheme is implemented in a digital signal controller. The battery charger has four operating modes in charging and two modes while discharging. The charger has in built current limit protection and the user may easily adjust the current limit and output voltage by adjusting the potentiometers provided in the charger. Auto mode in charging as well as in discharging modes reduces the user efforts. The charger draws an input current (at nearly full load) with a power factor of 0.96 and having THD <6%. The efficiency of the developed charger is found to be 88% and voltage ripple in the output voltage is less than 1%. The developed charger may discharge the battery at constant battery current and the energy stored in the battery may be given to utility grid at unity power factor without any additional circuitry or connections.

The system includes reduced input and output capacitor RMS currents and reduced EMI filtering requirements, decreased PCB size and better thermal performance. The battery used by the system is compact and low Life Cycle Cost (LCC) combined with its durability and flexibility are the ideal standard for railway energy backup. The developed charger may be used for applications where, output DC voltage varying from 110 volts to 900 volts. Use of high frequency ferrite transformer will helps to reduce the overall size and cost of the charger. Charger parameters can be remotely monitored by adding communication interfaces.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the disclosure and are not intended to be restrictive thereof. While specific language has been used to describe the disclosure, any limitations arising on account of the same are not intended. The figures and the foregoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, the order of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts need to be necessarily performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples.

Claims

WE CLAIM:

1. A system (10) for unity power factor based battery charger and discharger comprising: a dual mode subsystem (20) configured to operate in a charging mode and a discharging mode, wherein the dual mode subsystem (20) in the charging mode comprises: an input transformer (50) configured to provide isolation between battery (90) and grid, wherein the grid provides three phase input supply (30) though an incoming fuse (40); a boost rectifier (60) comprising a line choke (100) and an insulated gate bipolar transistor (IGBT) based bridge converter (70), wherein the boost rectifier (60) is configured to provide AC voltage to DC voltage conversion of the three phase input supply (30) with power factor correction, wherein the power factor correction is obtained by, a PI controller (172) configured to: obtain a voltage error by sensing the DC voltage and compare the DC voltage with a predetermined DC voltage; and produce a first reference current based on obtained voltage error; and a phase lock loop control system (160) configured to: multiply the reference current obtained through the PI controller with at least three unity magnitude sinewaves generated using the three phase input supply to obtain a multiplied output; and produce a second reference current for a current controller based on the multiplied output to obtain a unity power factor; and an interleaved buck/boost converter (80) coupled to the boost rectifier (60), wherein the interleaved buck boost converter (80) is configured to: multiply switching frequency by a predefined factor to half a ripple content and EMI filtering requirements for the capacitors and inductors thereby reducing the ripple content of voltage fed to the battery; adjust the voltage based on the DC voltage sensed by the boost rectifier to control a charging current of the battery (90); and the dual mode subsystem (20) in the discharging mode comprises: the interleaved buck/boost converter (80) configured to boost the output voltage of the battery (90) to a voltage required at the boost rectifier (60), wherein the boost rectifier (60) act as an inverter and configured to feed back the charge from the battery (90) into the grid at unity power factor obtained in the charging mode by converting the DC voltage into AC voltage via the IGBT based bridge converter (70).

2. The system (10) as claimed in claim 1, wherein the charging mode comprises a power flow from the grid to the battery and the discharging mode comprises the power flow from the battery to the grid.

3. The system (10) as claimed in claim 1, wherein the IGBT based bridge converter (70) comprises at least six IGBT switches (150), a DC link capacitor (140) and an input inductor (130) to provide continuous input current, wherein the at least six IGBT switches are configured to control pulses by a sine PWM obtained from the digital signal controller.

4. The system (10) as claimed in claim 1, wherein the interleaved buck/boost converter (80) having a multiphase buck converter comprises at least two buck converters in parallel, wherein each of the at least two buck converters comprises a switching control signal with phase difference of 360°/N, N is phase number.

5. The system (10) as claimed in claim 4, wherein the multiphase buck converter is configured to combine a plurality of phase shifted inductor currents from individual channel and reduce the total current ripple flowing into an output capacitor.

6. The system (10) as claimed in claim 1, wherein the interleaved buck/boost converter (80) is configured to: sense the battery voltage and compare with a reference battery voltage to generate an error voltage; provide the error voltage as an input to the PI controller to obtain a reference current; compare the reference current with battery current to generate an error current; provide a control signal for PWM generation by providing the error current to the PI controller; and produce two pulses stream having 180° phase difference based on the control signal a plurality of switches.

7. The system (10) as claimed in claim 1, wherein the dual mode subsystem (20) comprises a digital signal processing controller (110) configured to: control operations of the input transformer, the boost rectifier and the interleaved buck/boost converter; scale and convert battery voltage, battery current and DC link voltages to digital signals; and control the width of pulses applied to a gate terminal of IGBT and thereby control the output voltage and phase of the input current;

8. The system (10) as claimed in claim 7, wherein the digital signal processing controller (110) is configured to measure temperature of one or more heat sink mounted on each IGBT via one or more temperature sensors (112) to avoid breakdown of the battery charger and discharger.

9. A method (200) comprising: providing, by an input transformer, isolation between battery and grid, wherein the grid provides three phase input supply though an incoming fuse; (210) providing, by a boost rectifier comprising a line choke and an IGBT based bridge converter, AC voltage to DC voltage conversion of the three phase input supply with power factor correction, (220) wherein the power factor correction is obtained by obtaining, by a PI controller, a voltage error by sensing the DC voltage and compare the DC voltage with a predetermined DC voltage; (230) producing, by the PI controller, a first reference current based on obtained voltage error; (240) multiplying, by a phase lock loop control system, the reference current obtained through the PI controller with at least three unity 23 magnitude sinewaves generated using the three phase input supply to obtain a multiplied output; (250) producing, by the phase lock loop control system, a second reference current for a current controller based on the multiplied output to obtain a unity power factor; (260) multiplying, by an interleaved buck/boost converter, switching frequency by a predefined factor to half a ripple content and EMI filtering requirements for the capacitors and inductors thereby reducing the ripple content of voltage fed to the battery; (270) adjusting, by the interleaved buck/boost converter, the voltage based on the

DC voltage sensed by the boost rectifier to control a charging current of the battery; (280) boosting, by the interleaved buck/boost converter, the output voltage of the battery to a voltage required at the boost rectifier in discharging mode; (290) and feeding, by the boost rectifier, the charge from the battery into the grid at unity power factor obtained in the charging mode by converting the DC voltage into AC voltage via the IGBT based bridge converter in discharging mode. (300)