FIELD OF INVENTION
The present invention relates to an improved transformer less, three-phase, high capacity battery charger and more particularly to a transformer less, high frequency and current controlled battery charger system with power factor correction.
BACKGROUND OF THE INVENTION
Conventional charging systems require the use of a power transformer. The conventional power transformer usually functions to isolate the DC output of a battery charger and the charged batteries from the AC power line. They reduce the AC line voltage to a value compatible with a vehicle battery voltage. In general, the transformer operates at the line frequency (50-60 Hz). In some recent designs transformers have operated at higher frequencies, typically several kilohertz, with the aid of switching-transistor choppers. This higher frequency reduces the required size and weight for the transformer.
AC to DC switching power converters that provide both input to output isolation and power factor correction (PFC), may consist of a single-phase, single-stage flyback topology. If a large "hold up" energy-storage capacitor across the DC input bus is omitted and a control is appropriate, the AC input current can be controlled to be proportional to the AC input voltage. This produces unity power factor. A number of commercially manufactured integrated circuit flyback-topology controllers are available for this application. Some examples are1. Unitrode UC3852, Motorola MC342621 and Micro-Linear ML4813. All 3 may be used with a flyback transformer, to provide DC isolation.
One characteristic of this single-phase, single-stage PFC flyback topology is the
absence of "hold up" time. Another characteristic is that there will be
considerable DC output voltage ripple because output power droops during the
low voltage portions of the AC input sine wave. These two characteristics are not
important for many loads. In this situation the flyback converter becomes
advantageous because the converter operates well without capacitor.
Flyback converters are cost effective for power factor corrected applications at power levels below a few hundred watts. However at higher power and relative to other topologies, flyback converters suffer from the following weaknesses:
1. Higher peak voltages and currents in a solid-state power switch
2. Larger main transformer.
3. Higher RMS ripple current in an output capacitor.
US Patent No 4,389,608 discloses transformer less, battery-controlled, battery charger system which is intended to be carried on-board electrically-operated vehicles such as electric cars, golf carts, or light-weight industrial vehicles. The charger is of comparatively smaller capacity.
US Patent No 4,774,449 discloses a transformer less battery charger having a circuit for connecting the battery to an A.C. power source to supply charging current to the battery. An electronic switch in the form of a TRIAC or SCR is connected in series with the battery. The electronic switch is normally non-conductive thereby keeping open the charging circuit for the battery. This is SCR based single phase charger.
US Patent No 4,482,856 discloses a bridged, transformer less charger which permits the use of inexpensive low power diodes and a battery saver which may be used to permit excess energy to charge batteries.
US Publication No 20060033473 method and apparatus for charging batteries includes using single phase input rectifier to receive an ac input and provide a DC signal..
US Publication No 20030038612 a single phase battery charger for charging high voltage battery strings includes a DC-to-AC converter that drives the primary of a transformer having multiple secondaries.
US Publication No 4,200,830 discloses an inverting circuit of the series resonant type and including a pair of SCR's operated at variable off-times for controlling the charging of a battery.
US Patent No 4,321,523 discloses a transformer less battery charging circuit including a rectifier, a semiconductor switch in series with the battery, a sensing network monitoring the battery voltage, a trigger circuit responsive to the sensed battery voltage for controlling operation of the semiconductor switch and a voltage regulator for regulating output voltage of the rectifier which is supplied to the triggering and the battery voltage sensing networks.
Applicant's own patent application no 1785/Del/2007 is a "DSP controlled triple conversion online UPS with remote monitoring". In this invention, power factor \i corrected through the input power interface card, PFC choke and PFC booster power module. PFC & booster power module is controlled by PFC & booster controller to provide DC power to the DC bus. Single phase charger with PFC is being used in this invention.
US Patent No 5,731,969 discloses a solid-state, PFC power converter for converting 3-phase AC to DC in a single," isolated conversion step, using three forward converters. A transformer is present in the output section.
US Patent No 6,803,746 7,301,308 and Publication No 20050046387 discloses a highly efficient fast charger and methods for fast charging of high capacity batteries. There is no power factor correction.

US Patent No 5371456 discloses power charger apparatus for supplying electrica! power to an electrical device for operation or to a battery for charging, or both. There is present a transformer in the output section.
JP2007037225 discloses a charging circuit of a constant current charge system. This system charges a battery through low charge current supply capacity charger. This is a single phase charger.
ES2120358 is a single phase, portable, high frequency battery charger without power factor correction.
UA74875 discloses a single phase charger for accumulator batteries. There is an optoelectronic elements for isolating electric circuits.
JP2001103685 discloses power factor correction type single step induction charger 10 used for charging a battery. This is a single phase charger with transformer in the circuit.
JP2002262474, JP2004159414, JP2006296118, JP2005245145, JP2006174612, JP2006204021 and US Publication No 20070229028 discloses a charger for secondary batteries. In this system fluctuation in battery voltage is prevented in transition from constant-current charging to constant-voltage charging. This is single phase charger without of PFC.

US Patent No 5,773,955 discloses a battery charger which supplies charging current for a high voltage, high current battery in accordance with a charge profile. There is a passive power factor correction.
US Publication No 20060164035 discloses a battery charger for charging rechargeable batteries and/or battery packs. The charger can apply two modes of charging a battery. There is no active power factor correction in the charger.
GN1738148 is a battery charger, comprising an input rectifier filter circuit, a high frequency inverse-excited converter circuit, an output rectifier filter circuit, an auxiliary power circuit, and a temperature detection-control circuit. There is no power factor correction.
JP2005341769 discloses a charger which is highly efficient, suppress temperature rise and finishes charging in a short time using the current-limiting function of an external power supply. This is single-phase charger without of PFC.
US Patent No 5,994,872 discloses a battery charger which supplies charging current for a high voltage, high current battery. There are six IGBT's for rectification in the charger. The power converter is operable to supply unidirectional charging current to a battery which may be for powering an

eiectric vehicle. In such instance, the battery would actually be a string of batteries typically having an operating voltage of 300 volts or more,
Reference is to be made of the article by Sebastiao de Andrade, IEEE, 1996. This paper presents the analysis of an isolated three-phase converter operating in soft-commutation as a battery charger. The structure works with high power factor without intermediate circuits. Its main features are: simplicity of control driver circuit and robustness of power circuits. Principle of operation, design procedure, simulation and experimental results obtained from a laboratory prototype (55 A/48 V) are presented.
Reference is to be made of the article by Zimmermann, C. Three-Phase Unity Power Factor AC/DC Convert 1999. The article explains the development and realization of a 8 kW battery charger with power factor correction (PFC) is described. The converter consists of two parts: The first part is an AC/DC converter based on a "VIENNA' topology with a controlled output voltage of
700V and mid point connection. The second part consists of two DC/DC converters with galvanic isolation and parallel outputs. The output current and voltage can be controlled in the ranges 0-28A and 0-280V.
There was therefore, a need for two IGBT based fully transformer less, high capacity three-phase battery charger with power factor correction circuit.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide transformer less charger which reduces weight, size and cost.
It is another object of the present invention to provide high frequency, switched-mode charger for very low ripple charging which reduces the internal losses of the battery, which in-turn reduces the temperature rise of the battery thus increasing the life of the battery.
It is yet another object of the present invention to provide input power factor correction which reduces input harmonics.current and results in an input power factor greater than 0.9. The variation in input power factor with respect to
mains input voltage change as well as with respect to the load variation is very minimal.
It is still another object of the present invention to develop a high capacity charger at high frequency in single module which increases simplicity and reliability of the charger. The current embodiment is designed for a capacity of 8KW, which can easily be changed to high capacities with minor power circuit modifications.
It is a further object of the present invention to use few components which reduces cost of the system.
The present invention relates to a transformer less, battery-charging system having three primary advantages over prior type charging systems. It operates at high frequency which reduces the ripple in charging, current and voltage for better charging and minimizes the temperature rise in battery. This increases the life of the battery. High energy efficiency benefits the user by reducing power consumption and cooler operation. It is relatively inexpensive. These advantages grew mainly from the elimination of the power transformer which is required with the conventional charging systems. The charger also works even if two of the three input phases are available.
The present battery charger is controlled from data received from all the batteries in a battery bank which provides "constant current constant voltage" (CCCV) charging. In constant current constant voltage charger or CCCV charger, initially charging current is kept constant and voltage is varied until specified voltage is achieved. Once the specified voltage is achieved, the voltage is kept constant and charging current is decreased till the charging is complete. So in one region current is kept constant and in other region voltage is kept constant. The charging voltage is kept at its peak in the "constant voltage" region for maintaining electrolyte levels, specific gravity and charge. Peak current protection, short circuit protection, an EMI interference filter, diode rectifier and a power factor corrected power module for maintaining input power factor are all provided in the present invention. A constant DC voltage is fed to a controlled charger power module which provides constant-current constant-voltage charging. The charger is a high capacity charger of 8KW, 20A-100A/12V-420V.
In a preferred embodiment the present invention provides an improved transformer less three-phase battery charger, having a converter unit for charging through a charging filter, a battery bank with DC power obtained by
rectifying and smoothing of generated power; characterized in that said converter unit comprises: a current sensing circuit for generating a current control signal corresponding to current m impedance charging filter; a voltage detection circuit for generating a voltage control signal corresponding to the battery voltage; and a control circuit for peak current control of charger, thereby controlling the switching operation so that charging current follows the selected control signal.
In an embodiment of the present invention, the provision of multiple outputs is available in the system.
In another embodiment the charger can be operated by using three-phase supply from the three-phase input.
In an embodiment an L-G noise filter may be used to reduce switching current noise conducted back onto the AC input lines.
The battery charger of the present invention is capable of operating at an overall efficiency greater than 90 %.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a block diagram of three phase input power factor corrected battery charger.
Figure 2 is a circuit diagram of power factor corrected power module, charger power module and output filter. t
Figure 3 is a circuit diagram of power factor and charger control.
Figure 4 is power supply for control and drive circuits.
DETAILED DESCRIPTION OF THE INVENTION
Reference may be made to Figure 1 indicating the overall view of the functionality of the system of the present invention, where a battery charger includes an input circuit 1 that receives 3-PH AC input. An EMI filter 2 is provided in the input circuit to reduce noise due to electromagnetic interference. A converter unit 3 provides a rectified DC
output using 3-phase bridge rectifier 4. A power factor correction (PFC) module
5 is added in the conversion unit 3 which improves the power factor and provides a high DC voltage (750V-900V). Use of an input charger filter (LC filter)
6 can reduce ripple and switching noise from high DC bus. High DC bus feeds the charger power module 7 which chops the high DC bus to a CCCV charging by using peak current control method 8. An output filter 9 is provided for removing ripples from charger which is connected to a battery bank 10. Step down mean 11 is provided for providing low voltage supply 12. Means 11 comprises a switch mode power supply (SMPS) having multiple isolated power supplies required for control and drive actions. A typical EMI filter 2 can remove common mode and differential mode noises which are being generated in the system. It has a LC filter arranged in a particular order. The bridge rectifier circuit 4 is available for AC/ DC conversion. An output capacitor in the circuit is selected to avoid line distortion at switching time. Peak voltage of this capacitor must be greater than peak voltage of rectifier output voltage. The charger is a high capacity charger of 8KW, 20A-100A/12V-420V.
In an embodiment, there is a provision for multiple outputs from the converter unit 3. Multiple outputs can be provided by using multiple charger modules 7.
Figure 2 shows the power factor corrected power module 5,,charger power module 7 and output filter 9. The converter unit 3 (Figure 1) is designed to operate in the switching frequency range of 20 kHz to 200 kHz for reducing ripples in charging current and voltage thereby reducing temperature rise in batteries. Two IGBTs are being used in the converter 3. As the rectification is done by diode- diode rectifier, one IGBT is used as a switching device for power factor control 3 and the other is switching device for charger control 7. The switching frequency is in the range of .20 kHz to 200 kHz and it balances cost, size and efficiency factors. The charger power module 7 together with the battery bank may be used as a power supply. The voltage sensing network in the circuit is set at the same point as though the circuit were being used only as e battery charger so that the battery approaches a full state of charge. An output filter 9 is a typical L-C filter used with conventional forward converters. Inductor L is sufficiently large to maintain continuous current mode during the switching cycle. Inductor (L) provides high AC impedance at the switching frequency across each converter output. The high AC impedance of the inductor isolates each converter. This permits the converter to operate independently of others at any switching phase or switching frequency with minimal interaction problems. Therefore the average AC input current drawn by a converter is proportional to current in inductor L multiplied by an "on percent" or duty (D) of that converter.

Figure 3 is a circuit diagram of power factor and charger control 8. It shows details of typical control hardware used to implement unity power factor and output voltage regulation. The control circuit is physically not very large and complex because it consists of two standard integrated circuits. Integrated controller is more cost efficient than designing the control circuit with multiple discrete versions. It is also possible to integrate a single version of the control circuit that will work with all output voltage regulation. Average current controlled mode is used for power factor correction and peak current control is used for charging. The power factor control circuit generates the PWM signal by sensing rectifier output, average inductor current and output DC voltage. PWM signal have a fixed frequency and variable duty cycle which keeps the input current from 3-phase mains in-phase with their respective voltage and thus improves the power factor. If individual converter duty is controlled to be proportional to its AC input voltage, its resulting AC input current will be proportional to its AC input voltage. This represents unity power factor for that converter. Each converter is controlled in this manner, producing 3-phase unity-power factor. There present a typical L-C filter. This eliminates switching spikes and input ripples of the charger. There is one driver in between the PWM signal and IGBT which increases current capability of PWM signal so it can drive IGBT properly.
In case of charging control, sensing signals are charging current and battery voltage. Maximum charging voltage is set in comparison of a reference signal. When charger starts, first charging current is kept constant by sensing it. When set voltage is achieved, the voltage is kept constant by decreasing charging current.
Figure 4 is the circuit diagram of power supply 12 for control and drive circuits. It is a small switch mode power supply (SMPS) having 3 to 4 isolated power supplies required for control action and drive action. This is basically a DC/DC converter. It can be controlled by some switching mechanism having internal/external MOSFET. It provides regulated output even in a wide range of input. It also provides isolated power supply that can be used for different drive action. The electronic switches effectively connect and disconnect energy storing inductor(s) to and from the input source or the output. By varying duty cycle: frequency or phase shift of these commutations, an output parameter (such as output voltage) is.controlled. The SMPS rapidly switches a power transistor between saturation (full on) and cutoff (completely off) with a variable duty cycle whose average is the desired output voltage. The resulting rectangular waveform is low-pass filtered with an inductor and capacitor. The main advantage of this method is greater efficiency because the switching transistor (IGBT) dissipates little power in the saturated state and the off state compared
to the semi conducting state (active region). Other advantages include smaller size and lighter weight (from the elimination of low frequency transformers which have a high weight) and lower heat generation from the higher efficiency.
Output filters 9 are "averaging" energy transfer rate and assure continuous power flow into the load.
Fig 5 is constant current constant voltage (CGCV) characteristic curve. Initially charging current is kept constant and voltage is varied until specified voltage is achieved. Once the specified voltage is achieved, the voltage is kept constant and charging current is decreased till the charging is complete. So in one region current is kept constant and in other region voltage is kept constant. The charging voltage is kept at its peak in the "constant voltage" region for maintaining electrolyte levels, specific gravity and charge.

WE CLAIM
1. An improved transformer less three-phase battery charger, having a converter unit for charging through a charging filter, a secondary battery with DC power obtained by rectifying and smoothing of generated power; characterized in that said converter unit comprises: a current detection circuit for generating a current control signal corresponding to a charging current to the battery bank; a voltage detection circuit for generating a voltage control signal corresponding to the battery voltage; a current detection circuit for generating a current detection signal corresponding to the current passing through the impedance of said charging filter; a voltage .detection circuit for generating a voltage control signal corresponding to the battery voltage; and a control circuit for peak current control of charger, thereby controlling the switching operation so that charging current follows the selected control signal.
2. The battery charger as claimed in claim 1, wherein a switch mode power supply (SMPS) is provided haying multiple isolated power supplies required for control and drive actions.

3. The battery charger as claimed in the preceding claims, wherein said converter unit is provided with a power factor correction module with a average current control means for improving the power factor and providing high DC voltage for charging secondary battery.
4. The battery charger as claimed in the preceding claims, wherein the converter unit is provided with a charger power module for receiving high DC bus, said peak current control means provided for chopping said high DC bus to a constant current charging.
5. The battery charger as claimed in claim 1, wherein said charger is a high capacity charger of 8KW, 20A-100A/12V-420V.
6. The battery charger as claimed in claim 1, wherein said converter unit is designed to operate at high frequency of 20 to 200 kHz for reducing ripples in charging current and voltage, reducing the temperature rise in battery.
7. The battery charger as claimed in claim 1, wherein said charger can be operated using three-phase supply from the three-phase input.

-22-The battery charger as claimed in claim 1, wherein there is a provision for multiple outputs from the converter unit.
The battery charger as claimed in claim 1, wherein the overall efficiency of the charger is greater than 90 %.
An improved transformer less three-phase battery charger, having a converter unit for charging through a filter, substantially as herein described and illustrated in the figures of the accompanying drawings.