FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
AND
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION:
A system and method for online estimation of speed-load characteristics for integrated power electronics and variable speed generator.
APPLICANT :
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR (S):
Hassan Hafiz Imtiaz; Saha Raja and Wachasundar Shripad of Crompton Greaves Limited, Electronic Design Centre, Aryabhatta building, CG Global R&D Centre, Kanjurmarg (East), Mumbai - 400042, Maharashtra, India; all Indian nationals.
PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF THE INVENTION:
This invention relates to the field of power electronics and their control systems.
Particularly, this invention relates to a system and method for online estimation of speed-load characteristics for integrated power electronics and variable speed generator.
BACKGROUND OF THE INVENTION:
Electrical components, devices, equipment require a continuous feed of electric power for their working. One such example of a system which requires continuous electric power is a telecommunication tower. A failure to power such a tower is catastrophic to the telecommunication network.
Hence, back-up power supply is provided to such electrical components. Back-up power supply may be provided by a diesel generator. A diesel generator is the combination of a diesel engine with an electrical generator (often called an alternator) to generate electrical energy. Diesel generating sets are used in places without connection to the power grid, as emergency power-supply if the grid fails. Sizing of diesel generators is critical to avoid low-load or a shortage of power and is complicated by modern electronics, specifically non-linear loads.
During the switching from a main supply to a back-up supply, the speed of the diesel engine of the generator needs to be set in accordance with the load that is to be served. Hence, according to the prior art system and method, a speed load characteristic monitor and adjustment is provided so that the diesel generator speed can be set in accordance with the load. If this same system and method is followed

for a variable speed integrating generator, the engine has to cater to losses of generator and power electronics converter connected to the system, thereof. Many a times, the manufacturer of alternators, power electronics, diesel generator; all components of a back-up power system are different. Hence, there is no common platform for accurate detection of optimum speed at which generator should operate at a given load, because losses occurring at the alternator and power electronics which are further in line after the generator cannot be accounted for. This leads to a non-optimum generator operation, resulting in fuel losses. Eventually, this may result in depreciation of life or health of components of the back-up power supply system.
Hence, there is a need for finding out an integrated speed load characteristic for efficient operating of the back-up power supply system.
OBJECTS OF THE INVENTION:
An object of the invention is to provide a system which provides an optimum speed load curve and employs the optimum speed load curve to vary the speed of a generator.
Another object of the invention is to provide a system which reduces fuel consumption of a generator.
Yet another object of the invention is to provide a system which provides optimum speed for a generator for any load serviced by the generator.
Still another object of the invention is to account for losses occurring in the backup power supply system.

Another object of the invention is to provide a system which calculates an optimum speed load curve using total harmonic distortion (THD) of a signal.
SUMMARY OF THE INVENTION:
According to this invention, there is provided a system for online estimation of speed-load characteristics for integrated power electronics and variable speed generator, said system comprises:
a) initialisation means adapted to provide initial readings for maximum speed and corresponding total harmonic distortion value of said generator;
b) step defining means adapted to define steps of incremental speed values for said generator;
c) tolerance band defining means adapted to define a tolerance band for percentage change in total harmonic distortion value per unit increment step of speed of said generator in order to provide a defined value;
d) monitoring means adapted to monitor total harmonic distortion value in a real-time manner;
e) computation means adapted to compute change in total harmonic distortion value per unit increment step of speed of said generator in order to provide a computed value;
f) comparator means adapted to compare said computed value with said defined value; and
g) speed changing means adapted to change speed of said generator in relation to output of comparator to obtain an optimum speed of said generator such that corresponding computed value is less than said defined value.
Typically, said initialisation means includes maximum speed reading means adapted to adjust said generator to its maximum rated speed and to read said maximum rated speed.

Typically, said initialisation means includes minimum total harmonic distortion value reading means adapted to adjust said generator to its maximum rated speed and to read corresponding minimum total harmonic distortion value.
Typically, said step defining means is a pre-determined step defining means adapted to define steps considering the maximum rated speed and in accordance with pre-determined formulae.
Typically, said tolerance band defining means is a pre-determined tolerance band defining means adapted to define a percentage change band for THD can be defined using pre-determined formulae depending upon the minimum value of THD and incremental steps, which percentage change is the tolerance band.
Typically, said system includes monitoring means adapted to monitor total
harmonic distortion value for every step change in the speed of operation of said
generator.
Typically, said computation means includes means to read previous total harmonic
distortion value and changed total harmonic distortion value to achieve a computed
percentage of change, thereby providing a computed value (THD-vin).
Typically, said system includes a look-up database adapted to store total harmonic distortion values at discrete speed values for a given generator.
Typically, said system includes an updating means adapted to update a look-up database adapted to store total harmonic distortion values at discrete speed values for a given generator, said updating occurring when said computed value is less than said defined value.

According to this invention, there is provided a method for online estimation of speed-load characteristics for integrated power electronics and variable speed generator, said method comprises the steps of: i. providing initial readings for maximum speed and corresponding total
harmonic distortion value of said generator; ii. defining steps of incremental speed values for said generator; iii, defining a tolerance band for percentage change in total harmonic distortion
value per unit increment step of speed of said generator in order to provide a
defined value; iv. monitoring total harmonic distortion value in a real-time manner; v. computation means adapted to compute change in total harmonic distortion
value per unit increment step of speed of said generator in order to provide a
computed value; vi. comparing said computed value with said defined value; and vii. changing speed of said generator in relation to output of comparator to
obtain an optimum speed of said generator such that corresponding
computed value is less than said defined value.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
This invention will now be described in relation to the accompanying drawings, in which:
Figure 1 illustrates a schematic of a system used for supplying electric power to a load.
Figure 2 illustrates a schematic of a system used for supplying electric power to a load with the location for measuring total harmonic distortion;

Figure 3 illustrates a schematic of a system for online estimation of speed-load characteristics for integrated power electronics and variable speed generator; and
Figure 4 illustrates a flowchart of a method for online estimation of speed-load characteristics for integrated power electronics and variable speed generator.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
According to this invention, there is provided a system for online estimation of speed-load characteristics for integrated power electronics and variable speed generator.
Figure 1 illustrates a schematic of a system used for supplying electric power to a load.
A diesel generator (DG), an alternator (A), and power electronics (PE) are connected to a load (L) which requires the back-up electric power supply.
Figure 2 illustrates a schematic of a system used for supplying electric power to a
load with the location for measuring total harmonic distortion.
Total harmonic distortion can be measured at the point THD shown in Figure 2.
Figure 3 illustrates a schematic of a system for online estimation of speed-load characteristics for integrated power electronics and variable speed generator; and
In accordance with an embodiment of this invention, there is provided an initialisation means (IM) adapted to provide initial readings for total harmonic distortion of the generator. The initial readings include maximum speed (SP-max) of the generator and total harmonic distortion (THD-min) at maximum operating

speed of the generator. The generator is operated to its maximum rated speed. The system of this invention monitors and notes down the maximum rated speed. At this maximum rated speed (SP-max), the total harmonic distortion, or THE), of the back-up power supply is monitored and noted by the system of this invention. This is the minimum value of THD (THD-min).
The total harmonic distortion, or THD, of a signal is a measurement of the harmonic distortion present and is defined as the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency.
In accordance with another embodiment of this invention, there is provided a step defining means (SDM) adapted to define steps for incrementing speed of the generator. These steps are taken into account considering the maximum rated speed above. Definition of steps can be in accordance with pre-determined formulae.
In accordance with yet another embodiment of this invention there is provided a tolerance band defining means (TBM) adapted to define a tolerance band for change in THD per unit increment step of speed of the generator in order to provide a defined value. Depending upon the minimum value of THD and incremental steps, a percentage change band for THD can be defined using predetermined formulae, which percentage change is the tolerance band.
In accordance with still another embodiment of this invention, there is provided a monitoring means (MTM) adapted to monitor THD in a real-time manner. At the location shown in Figure 2 of the accompanying drawings, THD is continuously monitored. For every step change in the speed of operation of the motor, the TF£D at that instance is noted by the monitoring means.

In accordance with an additional embodiment of this invention, there is provided a computation means (CMP) adapted to compute change in THD per unit increment step of speed of the generator in order to provide a computed value. Previous THD value and changed THD value are used by the computation means to achieve a computed percentage of change, thereby providing a computed value (THD-vin).
In accordance with still an additional embodiment of this invention, there is provided a look-up database (DB) adapted to store THD values at discrete speed values for a given generator. The database is a relational database which adapted to store values of THD in a relation to tolerance band defined by speed of generator, for a specific generator.
In accordance with yet an additional embodiment of this invention, there is provided a comparator means (CP) adapted to compare the computed value with a stored value. If the computed value falls below the stored value, the optimum speed of generator is achieved. Else, the speed of the generator needs to be changed. This is an iterative mechanism of altering the speed, monitoring the THD value, comparing the THD value with a defined or stored THD value, and obtaining optimum speed of generator correlating to the THD value.
In accordance with another additional embodiment of this invention, there is provided a speed changing means (SCM) adapted to change speed of the generator in relation to output of comparator. If the compared value if positive, speed of generator is optimum, and these readings are updated in the database for further
use.
Figure 4 illustrates a flowchart of a method for online estimation of speed-load characteristics for integrated power electronics and variable speed generator.

According to this invention, there is provided a method for online estimation of
speed-load characteristics for integrated power electronics and variable speed
generator.
Step 1000-Start
Step 1001 - Set maximum speed reference for generator (SP-max)
Step 1002 - Read 3-phase AC Voltage
Step 1004 - Find THD of AC input voltage (THD-min)
Step 1006 - Reduce speed reference. Note down Current speed reference
Step 1008 - Find computed value (THD-vin)
Step 1010 - THD-vin > THD-min* 1.1 ? If Yes, Go to Step 1012. If No, Go to Step
1006
Step 1012 - Correct speed reference = current speed reference + delta speed
reference
Step 1014 - Note down load and speed. Update look-up table
Step 1016-Stop
While this detailed description has disclosed certain specific embodiments of the present invention for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We claim,
1. A system for online estimation of speed-load characteristics for integrated power electronics and variable speed generator, said system comprising:
a) initialisation means adapted to provide initial readings for maximum speed and corresponding total harmonic distortion value of said generator;
b) step defining means adapted to define steps of incremental speed values for said generator;
c) tolerance band defining means adapted to define a tolerance band for percentage change in total harmonic distortion value per unit increment step of speed of said generator in order to provide a defined value;
d) monitoring means adapted to monitor total harmonic distortion value in a real-time manner;
e) computation means adapted to compute change in total harmonic distortion value per unit increment step of speed of said generator in order to provide a computed value;
f) comparator means adapted to compare said computed value with said defined value; and
g) speed changing means adapted to change speed of said generator in relation to output of comparator to obtain an optimum speed of said generator such that corresponding computed value is less than said defined value.
2. A system as claimed in claim 1 wherein, said initialisation means includes maximum speed reading means adapted to adjust said generator to its maximum rated speed and to read said maximum rated speed.

3. A system as claimed in claim 1 wherein, said initialisation means includes minimum total harmonic distortion value reading means adapted to adjust said generator to its maximum rated speed and to read corresponding minimum total harmonic distortion value.
4. A system as claimed in claim 1 wherein, said step defining means is a predetermined step defining means adapted to define steps considering the maximum rated speed and in accordance with pre-determined formulae.
5. A system as claimed in claim 1 wherein, said tolerance band defining means is a pre-determined tolerance band defining means adapted to define a percentage change band for THD can be defined using pre-determined formulae depending upon the minimum value of THD and incremental steps, which percentage change is the tolerance band.
6. A system as claimed in claim 1 wherein, said system includes monitoring means adapted to monitor total harmonic distortion value for every step change in the speed of operation of said generator.
7. A system as claimed in claim 1 wherein, said computation means includes means to read previous total harmonic distortion value and changed total harmonic distortion value to achieve a computed percentage of change, thereby providing a computed value (THD-vin).
8. A system as claimed in claim 1 wherein, said system includes a look-up database adapted to store total harmonic distortion values at discrete speed values for a given generator.

9. A system as claimed in claim 1 wherein, said system includes an updating means adapted to update a look-up database adapted to store total harmonic distortion values at discrete speed values for a given generator, said updating occurring when said computed value is less than said defined value.
10. According to this invention, there is provided a method for online estimation of speed-load characteristics for integrated power electronics and variable speed generator, said method comprising the steps of:
i. providing initial readings for maximum speed and corresponding total
harmonic distortion value of said generator; ii. defining steps of incremental speed values for said generator; iii. defining a tolerance band for percentage change in total harmonic distortion
value per unit increment step of speed of said generator in order to provide a
defined value; iv. monitoring total harmonic distortion value in a real-time manner; v. computation means adapted to compute change in total harmonic distortion
value per unit increment step of speed of said generator in order to provide a
computed value; vi. comparing said computed value with said defined value; and vii. changing speed of said generator in relation to output of comparator to
obtain an optimum speed of said generator such that corresponding
computed value is less than said defined value.