DESC:FIELD OF THE INVENTION
[001] The present invention relates generally to an electric power supply system. More particularly it relates to an electric power supply system for enhancing efficiency of internal combustion engine driven electric generator and a method thereof.

DESCRIPTION OF THE BACKGROUND OF THE INVENTION
[002] An electric power supply system comprising of multiple power sources is often used as a power source for critical/sensitive applications that require uninterrupted power supply. The existing electric power supply system is described schematically in figure 1 wherein the same numerals indicate the same parts. The electric power supply system 100 comprises multiple input power sources such as an electrical grid 102, an internal combustion engine driven electric generator 104, and a power source monitoring and selection system 106. Generally, electric generators driven by internal combustion engines have long been used as a source of electricity for backup power as well as for primary power applications. The generator converts the mechanical energy supplied by internal combustion engine into electricity, which is used to power electrical loads such as lighting equipment, electric motors and heating coils. Depending on availability and quality of different power sources, and required output power, the power monitoring and selection system 106 selects one of the input power sources for powering the electric load 108/110.

[003] In many applications of such power supply system, the electric load 108/110 consists of two components. One component i.e. the electric load 108 which is sensitive to power quality attributes such as frequency and voltage, and requires these attributes to be within a tight tolerance band for correct operation. An example of such component is an air-conditioner. The other component i.e. the electric load 110 which can tolerate variation of the power quality attributes to a larger extent compared to the first component. An example of such component is a battery charging system. In many practical applications, the load component sensitive to power quality attributes operates in an intermittent fashion.

[004] Generally the electrical grid 102 is the main power supply to the load 108/110. When the electrical grid 102 is not healthy or voltage is less, then another available power supply source such as the generator 104 may be used. Depending on availability and quality of grid power supply, and requirement of output power, the power monitoring and selection system 106 gives command to start/stop the internal combustion engine driven electric generator 104.

[005] In most applications of the power supply systems, the internal combustion engine is operated in a narrow speed range. Since in the commonly used configuration of internal combustion engine driven electric generator, the power attributes such as electric frequency and voltage are directly proportional to engine speed, regulating engine speed in a narrow operating range ensures that power attributes are regulated within a narrow tolerance. Further, the power monitoring and selection system closely monitors the power quality attributes, and raises fault alarms if the attributes fall outside permissible limits. While this configuration ensures that the electrical load component which is sensitive to power quality attributes is operated in a correct manner, it also results in overall inefficient operation of internal combustion engine, as the engine operates in a narrow speed range irrespective of load on the engine.

[006] It is well known that efficiency of an internal combustion engine can be improved if the operating speed of the engine is varied over a wide range in response to load imposed on the engine. Operating the engine in such a manner in the existing power supply configuration will result in inappropriate working of electrical load component which is sensitive to power quality attributes. It will also result in fault alarms being raised by power monitoring and selection system.

[007] While it is possible to use a power converter to convert variable frequency, variable voltage output power of the internal combustion engine driven electric generator operated over a wide speed range into a fixed frequency, fixed voltage power, which can subsequently provide as an input to power monitoring and selection system. Addition of such power converter substantially increases cost of the system and introduces inefficiencies due to power conversion process.

[008] Considering the above there is need to provide a cost effective electric power supply system and a method for enhancing efficiency of internal combustion engine driven electric generator, while ensuring correct operation of the load component sensitive to power quality attributes and also not causing fault alarms.

SUMMARY OF THE INVENTION
[009] Disclosed herein an electric power supply system for enhancing efficiency of internal combustion engine driven electric generator comprising: an electrical grid coupled to a power source monitoring and selection system which selectively connects said electrical grid to a two-way switch; an engine driven electric generator coupled to said two-way switch and operated according to commands received from said power source monitoring and selection system; a power converter coupled to said power source monitoring and selection system for maintaining the power quality attributes of the output power within a narrow tolerance limit irrespective of corresponding power quality attributes of the input power; a load measurement module coupled to engine driven electric generator for measuring electrical load on said electric generator; and a speed governor unit in communication with said load measurement module and said electric generator; wherein when said power source monitoring and selection system selects engine driven electric generator as power source, said speed governor unit adjusts the speed of said engine driven electric generator to an optimum value based on the electrical load measured by load measurement module thereby providing desired electrical power to electrical load connected to two-way switch.

[010] In some embodiments, the speed governor unit comprises an electronic control unit and an actuator.

[011] In some embodiments, the low capacity power converter comprises a frequency converter.

[012] In some embodiments, the two-way switch comprises an electrically excited two-way power switch having two inputs and one output.

[013] Another embodiment of the invention includes a method for enhancing efficiency of internal combustion engine driven electric generator in an electric power supply system comprising the steps of: selecting engine driven electric generator as a power supply source based on the availability and required output power; measuring electrical load on the electric generator; communicating measured load to speed governor unit; and adjusting speed of the engine driven electric generator to an optimum level thereby maintaining the power quality attributes of the output within a narrow tolerance limit irrespective of corresponding power quality attributes of the input.

[014] In some embodiments, the operating speed of the engine is based on the load condition and is chosen such that the power quality attributes are maintained at the values desired by the load within an acceptable tolerance.

[015] Additional novel features shall be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following specification or may be learned by the practice of the invention. The invention may be better understood and further advantages and uses thereof more readily apparent when considered in view of the following detailed description of exemplary embodiments, taken with the accompanying drawings. These embodiments describe only a few of the various ways in which the principles of various other embodiments may be realized and the described embodiments are intended to include all such embodiments and their equivalents and the reference numerals used in the accompanying drawings correspond to the like elements throughout the description. The features and advantages of the invention may be realized and attained by means of the instrumentalities, combinations and methods pointed out in the appended claims.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[016] The above-mentioned and other features and advantages of the various embodiments of the invention, and the manner of attaining them, will become more apparent and will be better understood by reference to the accompanying drawings, wherein:
[017] Figure 1 is a schematic representation of existing electric power supply system; and
[018] Figure 2 is a schematic representation of electric power supply system according to present invention.

DESCRIPTION OF THE INVENTION
[019] In order to achieve the aforesaid and other objectives, according to the invention, a cost-effective electric power supply system and a method for enhancing efficiency of internal combustion engine driven electric generator is disclosed. The cost effective electric power supply system ensures the power monitoring system does not create fault alarms and the electric load component sensitive to power quality attributes is operated correctly.

[020] Figure 2 describes schematically a cost-effective electric power supply system 200 for enhancing efficiency of internal combustion engine driven electric generator. The system 200 comprises an electrical grid 202, an internal combustion engine driven electric generator 204, a power source monitoring and selecting system 206, a low capacity power converter 208, an electronic speed governor unit 210, a load measurement module 212 and an electrically excited two-way power switch 214. The low capacity power converter 208 may be an electric frequency converter.

[021] The electric frequency converter 208 is an electric power converter that maintains certain power quality attributes (frequency and voltage) of the output within a narrow tolerance limit irrespective of corresponding power quality attributes of the input. The electronic speed governor unit 210 comprises an electronic control unit (ECU) and an actuator. The electronic speed governor unit 210 maintains the speed of the internal combustion engine to a desired value in a closed-loop fashion by controlling quantity of fuel entering the engine. The load measurement module 212 measures the electrical load on the electric generator and communicates the same to the electronic speed governor unit 210. The electrically excited two-way power switch 214 is an electric system with two inputs and one output, in which depending on electric excitation, only one of the inputs is connected to the output.

[022] In the cost effective power supply system, the output of the electrical frequency converter 208 is fed to the power monitoring and selector unit 206, the output of which serves as one input to the electrically excited two-way power switch 214. The output of the electric generator 204 serves as the other input to the two way power switch 214. The electrical excitation to the two way switch is provided in such a manner that when the power monitoring and selector system 206 selects the engine driven electric generator 204 as the power source, the two-way switch 214 connects the input corresponding to the engine driven electric generator 204 to its output, while in all other situations, the two-way switch 214 connects the input corresponding to the power monitoring and selector unit 206 to its output.

[023] Based on the measured electrical load, the ECU of the electronic speed governor unit 210 decides the speed at which to operate the engine, and gives appropriate commands to the actuator such that engine speed is governed to the desired value. The decision regarding the speed at which to operate the engine is decided whether the electric load component 216/218 that is sensitive to power quality attributes is active or not active. If the load component 218 sensitive to the power quality attributes is active, then the engine speed is chosen such that the power quality attributes are maintained at the values desired by the load component with an acceptable tolerance. If the load component 216 sensitive to the power quality attributes is not active, then the engine speed is chosen based on electric load such that the fuel consumption of the engine is minimized.

[024] A method for enhancing efficiency of internal combustion engine driven electric generator in an electric power supply system is also disclosed. The method comprises the steps of: maintaining the power quality attributes such as frequency and voltage of the output within a narrow tolerance limit irrespective of corresponding power quality attributes of the input using the electric frequency converter, maintaining the speed of the internal combustion engine to a desired value using the electronic speed governor unit, measuring the electrical load on the electric generator using the load measurement module, communicating the measured electrical load to the electronic speed governor unit, selecting a power supply such as an electrical grid or a generator based on the availability and required output power using power monitoring and selection system. The output of the power monitoring and selection system serves as one input to the electrically excited two-way power switch, i.e. supplying one of the power supplies to the switch. Further, the output of the electrical frequency converter is connected to the power monitoring and selector system. The output of the switch is connected to a load component based on a condition. The speed at which to operate the engine is decided by the ECU of the speed governor unit based on the condition i.e. whether the electric load component that is sensitive to power quality attributes is active or not active. If the load component sensitive to the power quality attributes is active, then the engine speed is chosen such that the power quality attributes are maintained at the values desired by the load component with an acceptable tolerance. If the load component sensitive to the power quality attributes is not active, then the engine speed is chosen based on electric load such that the fuel consumption of the engine is minimized.

[025] The cost effective power supply system and method ensure that the efficiency of the engine electric generator is maximized, while ensuring correct operation of the load component sensitive to power quality attributes and also the power monitoring system does not cause fault alarms in spite of operation of internal combustion engine over a wide speed range. Since the electrical frequency converter does not need to be sized for passing full power of the electric generator, the system is cost-effective compared to the configuration where the full power of the electric generator is passed through a frequency converter.

[026] It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
,CLAIMS:We claim:
1. An electric power supply system for enhancing efficiency of internal combustion engine driven electric generator comprising:
an electrical grid coupled to a power source monitoring and selection system which selectively connects said electrical grid to a two-way switch;
an engine driven electric generator coupled to said two-way switch and operated according to commands received from said power source monitoring and selection system;
a power converter coupled to said power source monitoring and selection system for maintaining the power quality attributes of the output power within a narrow tolerance limit irrespective of corresponding power quality attributes of the input power;
a load measurement module coupled to engine driven electric generator for measuring electrical load on said electric generator; and
a speed governor unit in communication with said load measurement module and said electric generator; wherein
when said power source monitoring and selection system selects engine driven electric generator as power source, said speed governor unit adjusts the speed of said engine driven electric generator to an optimum value based on the electrical load measured by load measurement module thereby providing desired electrical power to electrical load connected to two-way switch.

2. An electric power supply system as claimed in claim 1, wherein said speed governor unit comprises an electronic control unit and an actuator.

3. An electric power supply system as claimed in claim 1, wherein said low capacity power converter comprises a frequency converter.

4. An electric power supply system as claimed in claim 1, wherein said two-way switch comprises an electrically excited two-way power switch having two inputs and one output.

5. A method for enhancing efficiency of internal combustion engine driven electric generator in an electric power supply system comprising the steps of:
selecting engine driven electric generator as a power supply source based on the availability and required output power;
measuring electrical load on the electric generator;
communicating measured load to speed governor unit; and
adjusting speed of the engine driven electric generator to an optimum level thereby maintaining the power quality attributes of the output within a narrow tolerance limit irrespective of corresponding power quality attributes of the input.

6. The method as claimed in 5, wherein operating speed of the engine is based on the load condition and is chosen such that the power quality attributes are maintained at the values desired by the load within an acceptable tolerance.