TECHNICAL FIELD
The subject matter described herein, in general, relates to an electrical power system of an automobile, and in particular, relates to an alternator.
BACKGROUND
Typically, an automobile is equipped with an electrical power supply system for supplying electrical power to various electric load requirements of the vehicle. The system generally includes a battery, which is charged by an alternator. Modem alternators have a voltage regulator, either inbuih or associated, to regulate the charging voltage supplied to the battery. The voltage regulator controls field current in order to produce a constant voltage at the stator output. Further, a set of rectifiers is provided in the alternator for converting AC signal to DC signal prior to supplying it to the battery.
Contemporary vehicles have varying power requirements; therefore, more than one system for providing voltage is utilized to satisfy the varying power needs. Vehicles, for example, use a 12V system to meet specific load requirements of electronic control unit (ECU) in addition to a 24V/42V system to meet requirements of other loads such as starter motor, accessory motors, actuators etc. As the sophistication of vehicle electrical system is increasing enormously, it is desirable to provide dual voltage systems in the vehicle that meets the varied requirements of various loads in the vehicle.
In order to meet the above-mentioned objective, many vehicle electrical systems could employ more than one alternator for generating dual voltage in the vehicle. However, this arrangement is costly and occupies more space. Further, the engine compartments of the modem vehicles are so crowded that it is difficult to install an additional altemator. It is fiirther possible to employ DC/DC converters, in some applications, to derive lower voltage. However, DC/DC converter is a costly technology and difficult to be located within engine cabin due to high levels of vibration and temperature seen within engine compartment.
There is, therefore, a need to provide a cost effective dual voltage altemator that generates electrical power at different voltages.
SUMMARY
The subject matter described herein is directed to an electrical supply system that supplies voltage to various loads, having varied voltage requirements, in an automobile.

The electrical supply system herein comprises a high voltage bus, a low voltage bus and an alternator. The high voltage bus comprises at least one high voltage battery and high voltage load. The low voltage bus comprises at least one voltage smoothening device, such as a low voltage battery or a capacitor, and a low voltage load. The alternator includes polyphase stator windings having a terminating end. The stator windings are further provided with tappings. The terminating ends of the windings are connected to a rectifying means. The rectifying means rectifies stator voltage and supplies the rectified voltage to a high voltage battery and the high voltage load. Further, the tappings from stator windings are connected to an electronic controller, which controls the voltage supply to the voltage smoothening device on the low voltage bus.
The electronic controller performs functions such as, deriving AC voltage from the alternator, rectifying the same and regulating the voltage across voltage smoothening device. The electronic controller further includes a plurality of switching elements connected to a control unit. The control unit comprises a voltage detecting means for detecting the voltage being supplied to the voltage smoothening device and the low voltage load. The voltage detecting means compares the voltage to a predetermined voltage thereby generating a first signal. A current detecting means for detecting output current flowing through the electronic controller is further implemented in the control unit. The current detecting means compares the output current to a predetermined current value thereby generating a second signal. The first signal and the second signal are fed to a triggering means further included in the control unit. The triggering means determines the instance at which the switching elements become conductive. Thus, the triggering means controls the switching elements based on the first and second signals.
The advantage of the present subject matter is that dual voltage system is realized in a cost effective manner. This approach eliminates the need for electrical systems implementing more than one alternator or use of DC/DC converter to meet the requirements of various loads. Further, the present electrical system is compact and cost effective. Moreover, the proposed system is free from EMI/EMC concerns due to use of low frequency switching of power devices.
These and other features, aspects, and advantages of the present subject matter will be better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts in a simplified

form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. BRIEF DESCRIPTION OF DRAWINGS
The above and other features, aspects, and advantages of the subject matter will be better understood with regard to the following description, appended claims, and accompanying drawings where:
Fig.l illustrates a sectional view of a dual voltage alternator in accordance with the present subject matter.
Fig.2 illustrates an electrical diagram of a dual voltage alternator according to one embodiment of the present subject matter.
Fig.3 illustrates the electrical diagram of a dual voltage alternator of Fig. 1 illustrating the details of the electronic controller.
Fig.4 illustrates the block diagram of a control unit present within the electronic controller of Fig. 3.
Fig.Sa, 5b and 5c illustrate the electrical diagram indicating the current path corresponding to conducting phase winding, according to one embodiment of the present subject matter.
Fig.6 illustrates the electrical diagram indicating the current path corresponding to conducting phase winding according to second embodiment of the present subject matter.
Fig.7 illustrates the electrical diagram of the dual voltage ahemator according to the third embodiment of the present subject matter.
Fig. 7a illustrates the electrical diagram indicating the current path corresponding to a conducting phase winding according to the third embodiment of the present subject matter. DETAILED DESCRIPTION
The present subject matter herein describes an electrical supply system for an automobile. The electrical supply system herein comprises a high voltage bus, a low voltage bus and an alternator for generating dual voltages, one corresponding to low voltage bus and the other corresponding to the high voltage bus. The high voltage bus comprises at least one high voltage battery and high voltage load. In one embodiment, the high voltage battery is a battery pack including a plurality of low voltage batteries.

connected in series to produce high voltage. The low voltage bus comprises at least one voltage smoothening device and a low voltage load. In one embodiment, the voltage smoothening device is a capacitor, preferably a super capacitor. In another embodiment, the voltage smoothening device is a battery. In one implementation, the lowest battery of the low voltage batteries of the high voltage battery pack, acts as the voltage smoothening device.
The alternator includes polyphase stator windings with a terminating end. The stator windings of the alternator are provided with tappings. The polyphase stator windings have a terminating end, connected to a rectifying means. The rectifying means, which includes diodes, rectifies stator voltage and supplies the rectified voltage to the high voltage bus and the high voltage load. Further, the tappings are connected to an electronic controller, which controls the voltage supply to the voltage smoothening device.
The electronic controller further includes a plurality of switching elements connected to a control unit. The number of the switching elements is equal to the number of the stator windings. Each of the polyphase stator winding is connected to the switching element. The switching element can be any one from the group of rectifiers, silicon control rectifiers (SCR), field effect transistors (FET) or insulated-gate bipolar transistors (IGBT).
Further, the control unit comprises a voltage detecting means for detecting the voltage being supplied to the voltage smoothening device and the low voltage load. The voltage detecting means compares the voltage to a predetermined voltage thereby generating a first signal. A current detecting means for detecting output current flowing through the electronic controller is further implemented in the control unit. The current detecting means compares the output current to a predetermined current value thereby generating a second signal. The first signal and the second signal are fed to a triggering means further included in the control unit. The control unit controls the switching elements based on the first and second signals.
The advantage of the present subject matter is that a dual voltage system for an electrical power system of an automobile is realized in a cost effective manner.
Fig.l exemplarily refers to a sectional view of a dual voltage alternator 100, hereinafter referred to as DVA 100, used for powering electric system of an automobile.

220A, 220B and 220C are connected to the switching devices 305A, 305B and 305C
respectively. The second AC output via the tappings 220 are rectified by a second rectifier bridge 307 formed by the switching elements 305 consisting of 305A, 305B, 305C and the diodes 230D, 230E, 230F. It may be noted that the diodes 230D, 230E, 230F take part in rectification of both first and second AC output voltages. The switching elements 305 are switched "ON" or "OFF" appropriately to maintain the voltage for low voltage bus. The voltage of the low voltage bus is sensed at a low voltage supply point 310.
The electronic controller 235 further includes a control unit 315, which controls the triggering of the switching elements 305. Referring to Fig. 4, which shows the block diagram of the control unit 315, a triggering means 405 is employed to turn on/off the switching elements 305A, 305B, 305C based on the voltage VL sensed at low voltage supply point 310. One of the ways of operation of triggering means for the case of SCR devices is explained as follows. The triggering means 405, used herein, is preferably a hysteresis controller or a PWM controller. A voltage detecting means 410 included in the control unit 315 senses the voltage VL. The voltage detecting means 410 is set to a predetermined voltage, which is a threshold voltage VT. The voltage detecting means 410 senses the voltage Vs at point 415 and compares the voltage Vs with the voltage VT. If the voltage Vs is greater than VT, the triggering means 405 do not provide the triggering pulse to the switching elements 305A, 305B, and 305C. Therefore, the switching elements 305 are switched "OFF". Alternatively, if the voltage Vsis smaller than VT, the triggering means 405 provides the triggering pulse to the switching elements 305.
The triggering means 405 is further coupled to a current detecting means 420, which is employed in the control unit 315. The current detecting means 420 detects the output current Cs flowing through the electronic controller 235. The current detecting means 420 is set to predetermined current value, called the threshold current Cy. The current CT is set to limit the maximum current flowing through the electronic controller 235. The current detecting means 420 compares the output current Cs with the current CT. If the current Cs is greater than the current Cj, the triggering means 405 do not provide the triggering pulse to the switching elements 305A, 305B, and 305C. Alternatively, if the current Cs is smaller than the current CT, depending on the voltage sensed at 310, the triggering means 405 provides the triggering pulse to the switching

The DVA 100 has a rotor 105, which is driven at a variable speed by an engine on a motor vehicle (not shown). The alternator may use any salient pole construction including claw pole rotor.
Fig.2 illustrates an electrical diagram 200 of DVA 100 including polyphase stator windings 205. As the rotor 105 rotates, alternating voltages VA, VB and Vc are induced in each of the corresponding phase windings 205A, 205B and 205C of the polyphase stator windings 205. The frequency of the alternating voltage generated in the polyphase stator windings 205 is directly proportional to the angular velocity of the rotor 105. The magnitude or amplitude of the voltage is also a function of rotor speed. A voltage regulator 210 controls the field current of the rotor 105, in order to regulate the voltage at a high voltage bus.
The phase windings 205A, 205B and 205C of the output winding have a neutral point 215 and respective terminating ends. Further, tappings 220A, 220B and 220C are employed on each of the corresponding phase windings 205A, 205B and 205C. The terminating ends of the polyphase stator windings 205 are connected to a conventional first rectifier bridge 225 in order to rectify the first AC output of the polyphase stator windings 205. The first rectifier bridge 225 consists of six diodes 230A, 230B, 230C, 230D, 230E and 230F, collectively called as 230. The first AC output herein is converted into DC output, which is fed to a high voltage battery pack 233 and a high voltage load 234. The negative terminal of the high voltage battery pack 233 is grounded. The high voltage battery supports starters, accessory motors, actuators etc. in the automobile.
Further, the tappings 220A, 220B and 220C are connected to an electronic controller 235. The electronic controller 235 senses and regulates voltage of a low voltage bus. The voltage, thereafter, is supplied to a voltage smoothening device 240 of say 12V and to a load 245 that is connected in parallel. The negative terminal of the voltage smoothening device 240 is grounded.
Fig.3 illustrates the electrical diagram 300 of a dual voltage alternator, which elaborates the details of the electronic controller 235 according to an embodiment of the present subject matter. The electronic controller 235 herein includes three switching elements 305A, 305B and 305C corresponding to the three phase windings 205A, 205B and 205C. In this example, silicon control rectifier (SCR) is used as the switching device while other devices such as MOSFET, IGBT etc could also be considered. The tappings

elements 305. Thus the triggering means 405 acts according to the trigger signals received from the voltage detecting means 410 and the current detecting means 420 and gives appropriate trigger signal to the switching elements 305. The triggering means 405 provides trigger signal to points 425, 430, and 435 that are connected to the gate terminals of the switching elements 305, in this case SCRs.
While simultaneously triggering all the switching elements in case of SCRs, only the appropriate SCRs would conduct depending on the voltage bias across its anode and cathode. It is also possible to realize triggering strategy individually for specific SCRs at appropriate instants within positive half cycle of corresponding phases and the strategy for switching other types of devices are also well known to a person skilled in the art.
Fig.Sa illustrates the electrical diagram 500 indicating the current path of low voltage system when the switching element 305A corresponding to the phase winding 205A is conducting according to one embodiment of the present subject matter. During the conduction of the switching element 305A, the current flows through the corresponding phase winding 205A till the tapping 220A. Through the tapping 220A, the current is passed to the switching element 305A for rectifying the second AC output. A smoothening inductor 505 receives the rectified output, which smoothens the current ripples, if any, present in the rectified output, while the voltage at the low voltage bus is smoothened by the voltage smoothening device 240. The current is then passed through the negative diode 230E of the first rectifier bridge 225. The current through the diode 230E is received by the phase winding 205C thereby completing the circuit. Thus, during the rectification process for the low voltage system, all turns of one of the windings and a portion of turns of another winding, till the tapping point, conducts the current.
A free wheeling diode 510 is connected across the negative terminal and ahead of inductor 505. Such a freewheeling diode 510 is to provide current path for the inductor 505 when all the switching elements are turned off
Similarly, Fig.5b illustrates the electrical diagram indicating the current path of low voltage system when the switching element 305B corresponding to the phase winding 205B is conducting according to the embodiment of Fig. 5a.
Similarly, Fig.Sc illustrates the electrical diagram indicating the current path of low voltage system when the switching element 305C corresponding to the phase winding 205C is conducting according to the embodiment of Fig. 5a.

Further, Fig.6 illustrates the electrical diagram 600 indicating the current path of low voltage system when the switching element 305A corresponding to the phase winding 205A is conducting according to second embodiment of the present subject matter. According to this embodiment, the second AC output via the tappings 220 are rectified by the second rectifier bridge 307 which consists of the switching elements 305A, 305B, 305C and the negative diodes 605A, 605B, 605C. During the conduction of the switching element 305A corresponding to the phase winding 205A, the current flows from the neutral point 215 to the switching element 305A via the tapping 220A. The rectified signal from the switching element 305A is passed to the voltage smoothening device 240 and the load 245, via the inductor 505. The current path is completed by passing the current to the phase winding 205C via the negative diode 605C. During the rectification process for low voltage system herein, a portion of the phase winding 205A i.e. until the tapping 220A and a portion of the phase winding 205C i.e. from tapping 220C to the neutral point conducts the current.
Fig.7 illustrates the electrical diagram of the dual voltage alternator according to the third embodiment of the present subject matter corresponding to dual voltage electrical system for automobile. In the present example, the dual voltage system is a 24V & 12V system. According to this example, the high voltage battery pack 233 comprises two low voltage batteries of 12V each. The voltage smoothening device 240 herein is the lower battery of high voltage battery pack 233. In other words, the voltage smoothening device 240, that acts as a low voltage battery in this example and another 12V battery together constitute 24V battery pack 233. The high voltage load 234 is connected across the high voltage bus and the ground. Similarly, the low voltage load 245 is connected across the lower battery of the high voltage battery pack 233. The lower battery herein, acts as the voltage smoothening device 240. In other embodiments, wherein the high voltage battery pack 233 is provided with more than two low voltage batteries, the lowest battery acts as the voltage smoothening device 240.
In this embodiment, where the high voltage system corresponds to 24 V, the potential difference between 240A and ground is regulated at a value equal to half of the potential difference between 233A and ground.
With respect to another embodiment, where the high voltage battery pack 233 corresponds to 36V, the potential difference between 240A and ground is regulated at

one-third of the potential difference between 233A and ground. In general, the voltage at 240A with respect to ground is maintained at appropriate proportions of the voltage at 233A with respect to ground.
According to this system, the second AC output via the tappings 220 are rectified by the rectifier 305 which consists of switching elements 305A, 305B, 305C and the negative diodes 230D, 230E, 230F.
Further, Fig.7a illustrates, the current path of the low voltage system, wherein.the switching element 305A corresponding to the phase winding 205A is conducting. The current flows from the neutral point 215 to the switching element 305A and passes to the smoothening device 240 and the load 245 via the inductor 505. The current path is completed by passing the current to the phase winding 205C via the negative diode 230E.
This type of arrangement helps to avoid the need for an additional voltage smoothening device for low voltage bus and the scheme could be extended for any dual voltage system.
The embodiments described above are only by way of examples and the present subject matter can be embodied in many other ways. The aforementioned versions of the subject matter and equivalent thereof have many advantages, including those, which are described below.
The advantage of the present subject matter is that an electrical power system is provided which generates electrical power at two different voltages. Further, the present system is compact and economic. This approach eliminates the need for electrical systems implementing more than one alternator or use of DC/DC converter to meet the requirements of various loads. Moreover, the proposed system is free from EMI/EMC concerns due to use of low frequency switching of power devices.
Although the subject matter has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternate embodiments of the subject matter, will become apparent to persons skilled in the art upon reference to the description of the subject matter. It is therefore contemplated that such modifications can be made without departing from the spirit or scope of the present subject matter as defined.

We claim:
1. An electrical supply system for supplying voltage to various loads in an automobile, said system comprising:
a high voltage bus comprising at least one high voltage battery pack 233 and a high voltage load 234; a low voltage bus comprising at least one voltage smoothening device 240 and a low voltage load 245; and an alternator 100 for charging said batteries and supplying voltage to said loads, said alternator 100 comprising,
polyphase stator windings 205 having a terminating end, wherein each of said stator windings 205 is provided with tapings 220, a rectifying means 225 for rectifying stator voltage and supplying said rectified voltage to said high voltage battery pack 233 and said high voltage load 234, and
an electronic controller 235 for controlling voltage supply to said voltage smoothening device 240 and said low voltage load 245, wherein said terminating end is connected to said rectifying means 225, and said tapings 220 are connected to said electronic controller 235.
2. The electrical supply system as claimed in claim 1, wherein said electronic controller 235 comprises:
a plurality of switching elements 305; and
a control unit 315 connected to said switching elements 305, said control
unit 315 comprises:
a voltage detecting means 410 for detecting voltage being supplied to said voltage smoothening device 240 and said low voltage load 245, wherein said voltage detecting means 410 compares said voltage to a predetermined voltage and generates a first signal, a current detecting means 420 for detecting current flowing through said electronic controller 235, wherein said current detecting means 420 compares said current to a predetermined current value and generates a second signal, and
a triggering means 405, wherein said first signal and said second signal are fed to said triggering means 405 and wherein triggering means 405 controls said switching elements 305 based on said first and second signals.

3. The electrical supply system as claimed in claim 1, wherein the number of said
switching elements 305 is equal to the number of said stator windings 205 and
wherein each of said polyphase stator windings 205 is connected to said switching
element 305.
4. The electrical supply system as claimed in claim 1, wherein said switching element 305 comprises at least one of a rectifier, a silicon control rectifier, a field effect transistor or an IGBT.
5. The electrical supply system as claimed in claim 1, wherein said voltage smoothening device 240 is a battery.

6. The electrical supply system as claimed in claim 1, wherein said voltage smoothening device 240 is a capacitor.
7. The electrical supply system as claimed in claim 1, wherein said high voltage battery pack 233 comprises a plurality of low voltage batteries, wherein the lowest of said plurality of low voltage batteries is said voltage smoothening device 240.