BACKGROUND

[0001] Embodiments of the present specification generally relate to a power generation system and a method of operation of the power generation system, and more particularly, to optimization of energy storage devices in a power generation system.

[0002] In a power generation system having a solar power source and energy storage devices, excess energy generated by the solar power source may be stored in the energy storage devices. Conversely, when an energy demand is high, in addition to the energy provided by the solar power source, the energy storage devices may discharge stored energy to meet the excess demand of energy. It may be noted that during initial design stage of the power generation system, capacities of the energy storage devices may be selected based on a calculation of a load and solar irradiance. However, over a period of time, the energy storage devices degrade resulting in a lower capacity. Further, solar charge controller may no longer be operating in Maximum Peak Power Tracking mode. Therefore, any excess energy from the solar power source cannot be stored in the energy storage devices. Hence, the amount of power fed into the energy storage device is reduced and as a result considerable solar power is spilled.

[0003] In order to circumvent the solar power spill, traditionally energy storage devices are replaced after certain percentage (for example, 50 % to 60%) of degradation. However, if the energy storage devices are replaced after a certain percentage of degradation, the remaining energy storage capacity of the energy storage devices is not entirely harvested.

[0004] Therefore, there is a need for optimizing life of the energy storage devices and thereby ensure maximum utilization of the energy storage devices.

BRIEF DESCRIPTION

[0005] In accordance with one aspect of the present specification, a power generation system is presented. The power generation system includes a direct current (DC) link, a solar power source coupled to the DC link, a first energy storage device, a second energy storage device, a controller coupled to the first and second energy storage devices and configured to determine at least one of a load demand, an input power, and operating parameters of at least one of the first and second energy storage devices, and at least one DC to DC converter configured to operate in at least one of a voltage control mode and a current control mode and selectively couple the first and second energy storage devices to the DC link when operating in the at least one of the voltage control mode and the current control mode.

[0006] In accordance with another aspect of the present specification, a method of operation of a power generation system is presented. The method includes determining, by a controller, at least one of a load demand, an input power, and operating parameters of at least one of first and second energy storage devices, operating at least one DC to DC converter in at least one of a voltage control mode and a current control mode, and selectively coupling at least one of the first and second energy storage devices to a DC link via the at least one DC to DC converter when operating the at least one DC to DC converter in at least one of the voltage control mode and the current control mode.

DRAWINGS

[0007] These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

[0008] FIG. 1 is a schematic representation of a power generation system, according to aspects of the present specification;

[0009] FIG. 2 is a schematic representation of one embodiment of the power generation system of FIG.1 , according to aspects of the present specification;

[0010] FIG. 2(a) is a flow chart representing a method for operation of power generation system of FIG. 2, according to aspects of the present specification;

[0011] FIGs. 2(b), 2(c), and 2(d) are schematic representations of different timelines of different embodiments of operation of the power generation system of FIG. 2; [0012] FIG. 3 is a schematic representation of another embodiment of the power generation system of FIG.1 , according to aspects of the present specification; and

[0013] FIG. 3(a) is a schematic representation of a timeline of one embodiment of operation of the power generation system of FIG. 3.

DETAILED DESCRIPTION

[0014] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terms“first,”“second,” and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Also, the terms“a” and“an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. The use of “including,”“comprising” or“having” and variations thereof herein are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “connected” and “coupled” are not restricted to physical or mechanical connections or couplings, and can include electrical connections or couplings, whether direct or indirect. The term“operatively coupled,” as used herein, refers to direct and indirect coupling. Furthermore, the terms“circuit” and“circuitry” and“controller” may include either a single component or a plurality of components, which are either active and/or passive and are connected or otherwise coupled together to provide the described function.

[0015] As will be described in detail hereinafter, various embodiments of a power generation system and a method for operating the power generation system are disclosed. The exemplary power generation system may be employed in doubly fed induction generator-based power generation applications, micro-power generation applications, small-scale energy generation applications, hybrid power generation applications, and/or larger-scale applications, such as power plants or power stations, and the like.

[0016] The power generation system includes at least two energy storage devices, a controller, at least one direct current (DC) to DC converter, a DC link, a pow er source, and DC to alternating current (AC) converters. The power generation system is configured to provide power to a grid, such as a utility grid or a micro grid, and/or a load. Further, the power generation system may be configured to receive power from a utility grid or micro grid. The exemplary method of operating the power generation system ensures optimal usage of the at least two energy storage devices, thereby prolonging life of the at least two energy storage devices. Further, the exemplary method of operating the power generation system enables maximum utilization of the at least two energy storage devices. Further, the exemplary method enables to efficiently couple the at least two energy storage devices to the DC link without changing circuit configuration/architecture of an existing power generation system.

[0017] Turning now to the drawings, FIG. 1 is a schematic representation of an exemplary power generation system 100 according to aspects of the present specification. In particular, FIG. 1 depicts a power generation system 100 coupled to a grid 102. The grid 102 may include a utility grid 102a or a micro grid 102b. The term ‘micro grid,’ as used herein, refers to a small-scale power grid that can operate independently or collaboratively with other small power grids. The term‘utility grid,’ as used herein, refers to an interconnected network having generating stations that produce electric power, high voltage transmission lines that transmit power from distant sources to demand centers, and distribution lines that connect to individual customers. The micro grid 102b has a smaller power rating compared to the utility grid 102a.

[0018] The power generation system 100 includes a DC to AC converter 108, a solar power source 1 10, a first energy storage device 112, a second energy storage device 1 14, a first DC to DC converter 1 16, a second DC to DC converter 118, an optional solar DC to DC converter 120, a DC link 122, a system controller 124, a converter controller 126, and a connecting node 128.

[0019] The term‘DC-to-DC converter’ as used herein, refers to a power electronic circuit that converts a source of direct current (DC) from one voltage level to another voltage level. The term‘DC to AC converter’ as use herein, refers to a power electronic circuit which converts a DC voltage to an AC voltage. The DC to AC converter may be alternatively referred to as an inverter. In the illustrated embodiment, the DC to DC converters 1 16, 118, 120 and the DC to AC converter 108 are bidirectional converters.

[0020] Each of the first and second energy storage devices 1 12, 114 may include a plurality of cells, batteries, battery banks, or the like. In one embodiment, each of the first and second energy storage devices 112, 1 14 may comprise a lead acid battery, a lithium ion battery, or the like. In one embodiment, the first and second energy storage devices 112, 114 may have a similar operating capacity. The term‘operating capacity,’ as used herein, refers to power storage capacity of an energy storage device.

[0021] In another embodiment, the first and second energy storage devices 1 12, 114 have different operating capacities. In one embodiment, the first energy storage device 112 is a newer, less used battery. In such an embodiment, the first energy storage device 112 has a high operating capacity and longer cycle life. The term‘cycle life,’ as used herein, refers to number of complete charge/discharge cycles that an energy storage device is able to support. Further in this embodiment, the second energy storage device 114 is an older, more used battery having a lower operating capacity and a shorter cycle life. In an even more specific example, the second energy storage device 112 may comprise a battery earlier employed in healthcare power supply systems, hybrid vehicles, electric vehicle charging systems, aircraft systems, similar power generation systems (such as the power generation system 100), and the like. The second energy storage device 112 may have some remaining useful life which may be utilized optimally in the power generation system 100.

[0022] In the illustrated embodiment, the solar power source 1 10 is coupled to the DC link 122 via the optional solar DC to DC converter 120. Additionally, the power generation system 100 is coupled to the grid 102 via the DC to AC converter 108. The first energy storage device 1 12 is coupled to the DC link 122 via the first DC to DC converter 116. Further, the second energy storage device 1 14 is coupled to the DC link 122 via the second DC to DC converter 118. The first and second DC to DC converters 116, 1 18 may enabl e independent operation of the first energy storage device 1 12 from the second energy storage device 1 14. In one example, the circulating current between the first and second energy storage devices 112, 1 14 may be reduced or eliminated. [0023] As noted hereinabove, the power generation system 100 includes the system controller 124 and the converter controller 126. Although these are shown as separate boxes for purposes of illustration, one or any number of units may be used to control the operations described herein. As used herein, the term“controller” refers to integrated circuits (ICs), a computer, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit (ASIC), application-specific processors, digital signal processors (DSPs), field programmable gate arrays (FPGAs), and/or any other programmable circuits.

[0024] In the illustrated embodiment, the converter controller 126 comprises a centralized converter controller operatively coupled to the DC to DC converters 116, 118, 120 and the DC to AC converter 108. The converter controller 126 is configured to control operation of the DC to DC converters 116, 118, 120 and the DC to AC converter 108. Specifically, the converter controller 126 may be configured to control switching of switches of the DC to DC converters 116, 118, 120 and the DC to AC converters 108. In another embodiment, each of the DC to DC converters 116, 118, 120 and the DC to AC converter 108 may have a dedicated controller instead of the centralized converter controller 126.

[0025] In one example of operation, the converter controller 126 is configured to operate the first DC to DC converter 116 and the second DC to DC converter 118 in at least one of voltage and current control modes. The voltage control mode involves establishing a determined voltage at the DC link 122. The current control mode involves controlling current flowing between the DC link 122 and at least one of the first and second DC to DC converters 116, 118. In one embodiment, at a specific time instant, both the first and second DC to DC converters 116, 118 may operate in the current control mode. Further, at another time instant, the first DC to DC converter 116 may operate in the voltage control mode and the second DC to DC converter 118 may operate in the current control mode or vice versa.

[0026] Additionally, the system controller 124 may be operatively coupled to the first energy storage device 112 and the second energy storage device 114 via corresponding battery management units (not shown in FIG. 1). The battery management units are battery control units integrated in the first and second energy storage devices 112, 114. In addition, the system controller 124 may be coupled to the converter controller 126, a load, the solar power source 110, and the DC link 122.

[0027] The system controller 124 may be configured to determine a load demand, an input power, and/or operating parameters of at least one of the first and second energy storage devices 1 12, 1 14. For example, the system controller 124 may be configured to receive operating parameters of at least one of the first and second energy storage devices 112, 114 from the converter controller 126 and the DC link 122 parameters. The term‘load demand’ as used herein, refers to amount of energy requirement of a load (not shown in FIG. 1) coupled to the power generation system 100. The term‘input power,’ as used herein, refers to power supplied by the solar power source 110 or any other power source to the DC link 122. In one example shown in FIG. 2, the input power is alternatively supplied by a variable speed diesel generator coupled to the DC link 122 via a corresponding converter.

[0028] The operating parameters of the first and second energy storage devices 1 12, 114 may include a state of charge, a rate of charging, a rate of discharging, a state of health, a voltage level, current, or combinations thereof. The term‘state of charge,’ as used herein, refers to a capacity of an energy storage device as a percentage of a maximum capacity. The state of charge is generally calculated using current integration to determine a change in capacity of an energy storage device over time. Additionally, the rate of charging and the rate of discharging of an energy storage device may be governed by C-rate. The C-rate is a measure of a rate at which an energy storage device is discharged relative to a maximum capacity. For example, 1 C-rate means that an energy storage device will fully discharge in 1 hour. Further, the term‘voltage level,’ as used herein, refers to a terminal voltage or an open-circuit voltage of an energy storage device. The terminal voltage is a voltage generated between energy storage device tenninals when a load is applied. The terminal voltage varies with respect to the state of charge and discharge/charge current. Furthermore, the open-circuit voltage (V) is a voltage generated between energy storage device terminals when no load is applied. The open-circuit voltage is dependent on the state of charge. In one embodiment, depending of chemistry of the energy storage device, the open-circuit voltage increases with increase in the state of charge.

[0029] Additionally, the system controller 124 may be configured to determine a first operating condition of the first energy storage device 112 and a second operating condition of the second energy storage device 114. The first operating condition includes a lower threshold of a capacity of the first energy storage device 112 and an upper threshold of the capacity of the first energy storage device 112. Similarly, the second operating condition includes a lower threshold of a capacity of the second energy storage device 114 and an upper threshold of the capacity of the second energy storage device 114.

[0030] The upper threshold of the capacity of the first energy storage device 112 may be different from the upper threshold of the capacity of the second energy storage device 1 14. For example, the lower threshold of the capacity of the first energy storage device may be 20% and the upper threshold of the capacity of the first energy storage device may be 80%. The lower threshold of the capacity being 20% refers to a condition when the energy storage device has 20% of available battery capacity to store charge. Similarly, the upper threshold of the capacity being 80% refers to a condition when the energy storage device has 80% of available battery capacity to store charge.

[0031] In certain embodiments and sequences, the first energy storage device 112 may be dischar ged till the upper threshold of the capacity of the first energy storage device 112 or the lower threshold of the capacity of the first energy storage device 1 12. In a similar manner, the second energy storage device 1 14 may be discharged till the upper threshold of the capacity of the second energy storage device 114 or the lower threshold of the capacity of the second energy storage device 1 14. In certain other embodiments, the first energy storage device 1 12 and the second energy storage device 114 may be fully discharged irrespective of set values of threshold to meet a load demand.

[0032] As noted hereinabove, the controller 124 is configured to determine the first and second operating conditions of the first and second energy storage devices 1 12, 1 14 based at least in part on the operating parameters of the first and second energy storage devices 1 12, 1 14. In one embodiment, the operating parameters of the first energy storage device 1 12 and the second energy storage device 1 14 are determined in real time. In one embodiment, the operating parameters of the first energy storage device 112 and the second energy storage device 114 are learnt periodically during a period of time employing artificial intelligence techniques, machine learning algorithms, neural networks, and the like. Further, in one embodiment, the first operating condition of the first energy storage device 112 and the second operating condition of the second energy storage device 1 14 are dynamically modified based on the periodically learnt operating parameters of the first and second energy storage devices 1 12, 1 14.

[0033] For example, if the state of health of the first energy storage device 1 12 has deteriorated over a period of time, the operating condition of the first energy storage device 1 12 may be modified. Specifically, in one example, the upper and lower thresholds of capacity of the first energy storage device 112 may be modified compared to an initial set value of the upper and lower thresholds of capacity of the first energy storage device 1 12.

[0034] In another example, if there is a solar forecast which estimates a higher value of input power from the solar power source 1 10 on a day 4 in comparison to an estimated value of input power on prior days, such as day 1 to day 3, the upper threshold of capacity' of the first and second energy storage devices 1 12, 114 may be modified. For example, if the upper threshold of capacity' of the first and second energy storage devices 112, 1 14 is initially set to 60%, the upper threshold of capacity of the first and second energy storage devices 1 12, 1 14 may be modified to 80% (to the extent that the battery health permits this higher threshold) by consuming the energy stored in the first and second energy storage devices 1 12, 114. The modification of the upper threshold of capacity of the first and second energy storage devices 1 12, 1 14 aids in charging the first and second energy storage devices 1 12, 1 14 to store substantially more energy. Accordingly, most of the power generated by the solar power source 110 on day 4 may be adequately stored in the first and second energy storage devices 1 12, 114. Hence, the solar spill on day 4 may be reduced significantly. Further, at a later day, such as day 6, the energy stored in the first and second energy storage devices 112, 114 may be provided to power the load, thereby reducing fuel consumption. If the upper threshold of capacity of the first and second energy storage devices 1 12, 1 14 is not modified based on the solar forecast, the excess power generated on day 4 may not be adequately stored in the first and second energy storage devices 112, 114 thereby leading to higher percentage of solar spill.

[0035] In yet another example, if the demand from the load is high, the first and second energy storage devices 1 12, 1 14 need to provide excess power to meet the higher load demand. Hence, in such scenarios, the first and second energy storage devices 1 12, 114 may need to discharge additional energy to meet the higher load demand. Accordingly, the upper threshold of capacity of the first and second energy storage devices 112, 114 may be modified. In one example, the upper threshold of capacity of the first and second energy storage devices 112, 114 may be modified from 60% to 80%. Accordingly, the first and second energy storage devices 1 12, 1 14 may be configured to provide comparatively more energy to the load, thereby enabling to meet the load demand.

[0036] Although the example of FIG. 1 depicts only two energy storage devices, use of any number of energy storage devices is envisioned. Moreover, although the embodiment of FIG. 1 depicts only the DC link 122, use of an AC link in the power generation system 100 is envisioned. Specifically, in certain such scenarios, power sources may be coupled to the AC link and AC power may be converted to DC power by power converters and provided to the DC link. 122. Further, coupling of the energy storage devices to AC side of the power generation system 100 via corresponding DC to AC converters is envisaged.

[0037] FIG. 2 is a schematic representation of a power generation system 200 according to aspects of the present specification wherein an additional power source is present. Specifically, FIG. 2 is a schematic representation of a doubly fed induction generator-based power generation system 200. The power generation system 200 is operatively couplable to the utility grid /micro grid 102. [0038] The power generation system 200 includes a variable speed engine 202, a doubly fed induction generator (DFIG) 204, a rotor-side conversion unit 206, a line- side conversion unit 208, the solar power source 1 10, the first energy storage device 112, the second energy storage device 1 14, the first DC to DC converter 116, the second DC to DC converter 1 18, the optional solar DC to DC converter 120, the DC link 122, the controller 124, and the converter controller 126.

[0039] The variable speed engine 202 is coupled to the DFIG 204 having a stator 210 and a rotor 212. Further, the rotor-side conversion unit 206 is coupled to the rotor 212 of the DFIG 204. The line-side conversion unit 208 is further coupled to the stator 210 of the DFIG 204. Further, the rotor-side conversion unit 206 is operatively coupled to the line-side conversion unit 208 via the DC link 122. The rotor-side conversion unit 206 and the line-side conversion unit 208 include an AC -DC converter, a DC- AC converter, a DC-DC converter, or combinations thereof.

[0040] Furthermore, the solar power source 110 is coupled to the DC link 122 directly or via the optional DC to DC converter 120. Moreover, the first energy storage device 112 is coupled to the DC link 122 via the first DC to DC converter 116. Additionally, the second energy storage device 1 14 is coupled to the DC link 122 via the second DC to DC converter 1 18.

[0041] In certain embodiments, the optional solar DC to DC converter 120 operates as a maximum power point tracker (MPPT) to provide maximum power from the solar power source 1 10 to the DC link 122. In certain embodiments, the optional solar DC to DC converter 120 may not be employed and the solar power source 1 10 may be coupled directly to the DC link 122. In such embodiments, one of the first DC to DC converter 116, the second DC to DC converter 1 18, and the line-side conversion unit 208 adjusts a voltage at the DC link 122 to obtain maximum power from the solar power source 110.

[0042] The converter control ler 126 is configured to control operation of the DC to DC converters 116, 118, 120. Specifically, the converter controller 126 is configured to control switching of the switches of the DC to DC converters 116, 118, 120. Further, the system controller 124 is configured to provide system control. Specifically, the controller 124 may be configured to detennine a load demand, an input power, and operating parameters of at least one of the first and second energy storage devices 1 12, 114. The system controller 124 may be configured to receive operating parameters of at least one of the first and second energy storage devices 112, 1 14 from the converter controller 126 and the DC link 122 parameters. Additionally, the system controller 124 may be configured to determine a first operating condition of the first energy storage device 1 12 and a second operating condition of the second energy storage device 114 base at least in part on the operating parameters of at least one of the first and second energy storage devices, 112, 114 and optionally based on the input power and/or the load demand.

[0043] Additionally, in one embodiment, the system controller 124 is configured to determine pattern of discharging or charging of the first and second energy storage devices 1 12, 114 via the respective DC to DC converters 116, 1 18. The term“pattern of discharging or charging,” as used herein, refers to the timing of discharging or charging. The first and second DC to DC converters 1 16, 1 18 are activated/deactivated by the converter controller 126 to enable discharging or charging of the first an second energy storage devices 1 12, 114 till determined thresholds via the respective DC to DC converters 116, 118. In one embodiment, a communication between the system controller 124 and the converter controller 126 enables such activation and deactivation.

[0044] With continued reference to FIG. 2, the power generation system 200 operates in two different system operating modes such as a grid-connected mode of operation and islanded mode of operation. The term 'grid-connected mode,’ as used herein, refers to a condition where the power generation system 200 is coupled to at least one of the utility' grid 102a and the micro grid 102b. During the islanded mode of operation, the power generation system 200 is in an islanded condition and is not coupled to the utility grid 102a or micro grid 102b.

[0045] FIG. 2(a) is a flow chart representing a method for operation of power generation system of FIG. 2, according to aspects of the present specification. Specifically, FIG. 2(a) represents different operating modes of the power generation system 200. At step 232, it is determined if the power generation system 200 is coupled to the grid 102. If the power generation system 200 is coupled to the grid 102, the power generation system 200 is operating in a grid-connected mode. Subsequently, a check is done to determine if voltage at the DC link 122 is set to a determined value using the line-side conversion unit 208, as depicted at step 233. If the voltage at the DC link 122 is set to the determined value using the line-side conversion unit 208 then at step 234, both the first and second DC to DC converters 1 16, 118 operate in a current control mode. Particularly, the first and second DC to DC converters 1 16, 118 are controlled by the converter controller 126 to operate in the current control mode. Hence, the current flowing between the at least one of the first and second DC to DC converters 116, 1 18 and the DC link 122 is controlled based on the operation of the first and second DC to DC converters 116, 1 18 in the current control mode, as represented at step 236.

[0046] If the power generation system 200 is not coupled to the grid 102a or 102b, the power generation system 200 is operating in the islanded mode. In this scenario, the voltage and the frequency at the DC link 122 may not be established by the grid 102a or 102b or the line-side power conversion unit 208. In this example, the control shifts from block 232 to block 238.

[0047] In another example, when the power generation system 200 is operating in a grid connected mode and if voltage at the DC link 122 is not set to the determined value using the line-side conversion unit 208, the voltage at the DC link 122 may need to be set to a determined value using one of the first and second DC to DC converters 116, 118. Hence, the control shifts from block 233 to block 238.

[0048] At step 238, one of the first and second DC to DC converters 1 16, 118 operates in a voltage control mode and other converter of the first and second DC to DC converters 116, 1 18 operates in a current control mode. In one example, the first DC to DC converter 1 16 is controlled by the converter controller 126 to operate in the voltage control mode. At this instance, the second DC to DC converter 1 18 is controlled by the converter controller 126 to operate in the current control mode. Accordingly, at step 239, the first DC to DC converter 1 16 contributes towards maintaining the determined value of voltage at the DC link 122.

[0049] When operating the first and second DC to DC converters 116, 118 in the current control mode/voltage control mode, the first and second energy storage devices 112, 114 are configured to be charged and discharged. Specifically, at steps 234 and 238 of FIG. 2(a), the first and second energy storage devices 1 12, 1 14 are configured to be charged and discharged in different patterns as described hereinafter. Different embodiments of charging and discharging of the first and second energy storage devices 1 12, 1 14 in the power generation system 200 is described with respect to following examples.

[0050] Example 1 : Operation of the pow er generation system 200 including the first energy^ storage device 1 12 and the second energy storage device 114 having same operating capacity and initially either in a more heavily charged state (FIG. 2(b)) or a more heavily discharged state (FIG. 2(c)).

[0051] With respect to FIG. 2(b), the first and second energy storage devices 1 12, 114 have the same operating capacity and are in a more heavily charged state. In this example, the first and second DC to DC converters 1 16, 118 operate in the current control mode and the first and second energy storage devices 112, 1 14 provide current to meet a load demand via the respective DC to DC converters. This current is provided from the first and second energy storage devices 1 12, 114 to the load via the DC link 122 to meet the load demand .

[0052] Specifically, FIG. 2(b) represents the timeline 240 of discharge of the first and second energy storage devices 112, 1 14 to meet the load demand during operation of the power generation system 200. Initially, such as at time ta=0, the first DC to DC converter 116 is activated and the second DC to DC converter 118 is in a deactivated state, as depicted at block 242. Further, during a time period, 0 to to, where to>0, the first energy storage device 112 is discharged till a lower threshold of capacity of the first energy storage device 1 12 via the first DC to DC converter 1 16, as represented at block 244. Accordingly, current is transmitted to the load via the first DC to DC converter 1 16. When the first energy storage device 112 is discharged till the lower threshold of capacity of the first energy storage device 112, the first DC to DC converter 1 16 is deactivated by the converter controller 126, as represented at block 246. Accordingly, the first energy storage device 1 12 is disconnected from the DC link 122.

[0053] Further, the second DC to DC converter 118 is activated, as depicted at block 246, by the converter controller 126 and is operational during a time period to to ti, where ti , to>0 and ti>to. During the time period to to ti , the second energy storage device 114 discharges till the lower threshold of capacity of the second energy storage device 1 14, as depicted at block 248. Accordingly, current is transmitted to the load via the second DC to DC converter 118. When the second energy storage device 114 is discharged till the lower threshold of the capacity of the second energy storage device 1 14, the second DC to DC converter 118 is deactivated by the converter controller 126, as represented at block 250. Accordingly, the second energy storage device 114 is disconnected from the DC link 122.

[0054] Again, the first DC to DC converter 1 16 is activated, as depicted at block 250, by the converter controller 126 and is operational for a time period ti to ti, where ti, t2>0 and t2>ti. During the time period ti to t2, the first DC to DC converter 1 16 is operational and the first energy storage device 112 is discharged till the upper threshold of capacity of the first energy storage device 1 12, as represented at block 252. When the first energy storage device 112 is discharged till the upper threshold of capacity of the first energy storage device 1 12, the first DC to DC converter 1 16 is deactivated by the converter controller 126, as depicted at block 254.

[0055] Further, the second DC to DC converter 118 is activated, as represented at block 254, by the converter controller 126 and is operational for a time period t2 to ts, where t.y t2>0 and ts>t2. During the time period t2 to t3, tire second energy storage device 114 is discharged till the upper threshold of capacity of the second energy storage device 1 14, as represented at block 256. When tire second energy storage device 114 is discharged till the upper threshold of capacity of the second energy storage device 1 14, the second DC to DC converter 118 is deactivated by the converter controller 126, as depicted at block 258. Accordingly, the required current that needs to be provided via the DC link 122 to meet the load demand is cumulatively provided by the first and second energy storage devices 112, 114 during a time period 0 to t3. The step by step discharge of the first and second energy storage devices 1 12, 1 14 aids in prolonging life of the first and second energy storage devices 112, 1 14 due to lesser depth of discharge during each discharge cycle.

[0056] Although the above-mentioned example refers to discharging of the first and second energy storage devices 112, 1 14 to specified thresholds, in certain scenarios, the first and second energy storage devices 112, 1 14 may be fully discharged. Hence, in this scenario, the life of the first and second energy storage devices 112, 114 is compromised in order to provide required power to a critical load. Although the example of FIG. 2(b) describes the discharge of the first and second energy storage devices 112, 114 to meet the load demand, in another embodiment, the first and second energy storage devices 112, 114 may be discharged to establish a certain voltage at the DC link 122. In this embodiment, one of the first and second DC to DC converters 1 16, 118 may be operating in the voltage control mode.

[0057] FIG. 2(c) represents timeline 260 of another embodiment of operation of the power generation system, wherein the first and second energy storage devices have the same operating capacities. Specifically, FIG. 2(c) represents the timeline 260 of charging of the first and second energy storage devices 1 12, 1 14 of the power generation system 200 when charging is needed and where excess input power available. In one example, the first and second energy storage devices 1 12, 1 14 are initially either at upper thresholds of the capacity of the respective energy storage devices or are fully discharged. In this embodiment, excess power is needed to be stored in the first and second energy storage devices 112, 114. The power may be provided from the utility grid 102a or the solar power source 110 or any other equivalent power source to the first and second energy storage devices 112, 1 14. As a result, current flows via the DC link 122 to the first and second energy storage devices 112, 1 14. As a result, the first and second energy storage devices 112, 1 14 are charged.

[0058] At time td=0, the first DC to DC converter 1 16 is activated and the second DC to DC converter is deactivated, as represented at block 262. Specifically, during a charging time period 0 to ta where t _a >0, the first DC to DC converter 116 is operational and allows flow of current to the first energy storage device 112. Accordingly, the first energy storage device 112 is charged till the lower threshold of capacity of the first energy storage device 112, as depicted at block 264.

[0059] When the first energy storage device 112 is charged till the lower threshold of capacity of the first energy storage device 112, the first DC to DC converter 116 is deactivated by the converter controller 126, as depicted at block 266. Further, the second DC to DC converter 118 is activated by the converter controller 126, as depicted at block 266. The second DC to DC converter 1 18 is operational for a time period tch= ta to tb where tb, ta>0 and tb>t _a . During the time period ta to tb, the second energy storage device 1 14 is charged till the lower threshold of capacity of the second energy storage device 114, as depicted at block 268. When the second energy storage device 1 14 is charged till the lower threshold of capacity of the second energy storage device 114, the second DC to DC converter 118 is deactivated by the converter controller 126, as represented at block 270.

[0060] Further, the first DC to DC converter 1 16 is again activated by the converter controller 126, as represented at block 270 and is operational for a time period tb to tc, where tb, t _c >0 and tc>tb. During the time period tb to tc, the first DC to DC converter 116 is operational and the first energy storage device 112 is fully charged as depicted at block 272. When the first energy storage device 112 is fully charged, the first DC to DC converter 116 is deactivated by the converter controller 126, as represented at block 274.

[0061] Furthermore, the second DC to DC converter 118 is activated by the converter controller 126, as represented at block 274, and is operational for a time period tc to ta, where td, tc>0 and td>tc. During the time period tc to td, the second energy storage device 1 14 is fully charged as depicted at block 276. When the second energy storage device 114 is fully charged, the second DC to DC converter 1 18 is deactivated by the converter controller 126, as depicted at block 278. Accordingly, the power provided by the utility grid 102a or the solar power source 110 is cumulatively stored in the first and second energy storage devices 1 12, 114 during the time period 0 to td. [0062] Example-2: Operation of the power generation system 200 having the first energy storage device 112 and the second energy storage device 1 14 having different operating capacities. In such an embodiment, at an initial stage rather than fully charging both energy storage devices, the energy storage device with the lower operating capacity may not be fully charged. In a specific embodiment, the first energy storage device 112 is initially in a frilly charged state and the second energy storage device 1 14 is in a partially charged state, for example, till the lower threshold of capacity of the second energy storage device 114.

[0063] Additionally, with respect to discharging in the Example-2, FIG. 2(d) is schematic representation of a timeline 280 of discharge of the first and second energy storage devices 1 12, 114 to meet load demand. At time t i=0 the first DC to DC converter 116 is activated and the second DC to DC converter 118 is deactivated, as represented at block 282. During a discharge time period 0 to tx, where t _x >0, the first DC to DC converter 116 is operational and the first energy storage device 112 is discharged till an upper threshold of the capacity of the first energy storage device 1 12, as represented at block 284. When the first energy storage device 1 12 is discharged till the upper threshold of capacity of the first energy storage device 112, the first DC to DC converter 116 is deactivated by the converter controller 126, as represented at block 286. Further, as represented at block 286, the second DC to DC converter 1 18 is activated by the converter controller 126 and is operational for time period tx to t _y , where tx, ty>0 and t _y >tx. During the time period tx to t _y , the second energy storage device 1 14 is discharged till the upper threshold of capacity of the second energy storage device 114, as represented at block 288. When the second energy storage device 114 is discharged till the upper threshold of capacity of the second energy storage device 114, the second DC to DC converter 118 is deactivated by the converter controller 126, as depicted at block 290. Accordingly, the required current that needs to be provided via the DC link 122 to meet a load demand, is provided mainly by the first energy storage device 112 and partially by the second energy storage device 114. Thus, the second energy storage device 1 14 is not unduly cycled and the life of the second energy storage device 1 14 is prolonged. [0064] In an alternative embodiment, when current needs to be provided via the DC link 122 to meet a load demand, the required current is provided mainly by fully discharging the second energy storage device 114 and partially discharging the first energy storage device 112, for example, till the lower threshold of capacity of the first energy^ storage device 112. Thus, the life of the second energy storage device 1 14 is compromised. However, the life of the first energy storage device 112 is prolonged due to partial discharging. In some other embodiments, operation may alternate with periods of more heavily using the first energy storage device and periods of more heavily using the second energy storage device.

[0065] In yet another embodiment of operation where energy storage devices have different operating capacities, selection of energy storage device for discharging is based on required ramp rate of power required to meet the load demand. For example, when an instantaneous current is required for powering a step change in a critical load, the converter controller 126 may activate the first DC to DC converter 116 and the first energy' storage device 1 12 is discharged. It may be noted that since the first energy·' storage device 1 12 has enhanced operating capacity' than the second energy storage device 1 14, the first energy storage device 112 has a higher rate of discharge capability' compared to a rate of discharge capability of the second energy storage device 1 14. The higher rate of discharge of the first energy storage device 1 12 enables the first energy storage device 112 to supply the instantaneous current to the critical load hi such a scenario, the second DC to DC converter 118 is maintained in a deactivated state.

[0066] In accordance with an exemplary method of operation of the power generation system 200 aids in prolonging life of the first and second energy storage devices 112 and 1 14. Further, both the first and second energy storage devices 1 12, 114 are optimally utilized. The operation of the power generation system 200 in other scenarios is also envisaged. Also, different initial conditions of the first and second energy storage devices 1 12, 114 in the different scenarios is anticipated. Further, although the example of FIGs. 2(b), 2(c), and 2(d) represent certain pattern of activation and deactivation of the first and second DC to DC converters 1 16, 1 18, other patterns of ac tivation/deacti vation of the first and second DC to DC converters 116, 1 18 is envisaged. Further, different patterns of discharging and charging of the first and second energy storage devices 112, 114 is envisaged.

[0067] Referring now to FIG. 3, a schematic representation of a power generation system 300 according to aspects of the present specification is presented hi the embodiment of FIG. 3, unlike the embodiment of FIG. 2, a single DC to DC converter 302 and a switching unit 304 are present between the first and second energy storage devices 112, 114 and the DC link 122. The switching unit 304 controls which of first and second energy storage devices 112, 114 is coupled to the DC to DC converter 302. The DC to DC converter 302 may be alternatively referred to as energy storage DC to DC converter.

[0068] The switching unit 304 may include a double pole switch, for example. In one example, the switching unit 304 is a manual switch or an automatic switch. In another embodiment, the switching unit 304 includes a mechanical contact or a semiconductor switch.

[0069] FIG. 3 also illustrates a controlled power source 104 coupled to the connecting node 128 of the DC link 122 via the AC to DC converter 106. Although in the example of FIG. 3, the controlled power source 104 is coupled to the DC link 122 via the AC to DC converter 106, in one embodiment, the power generation system 300 may not have the controlled power source 104 and the AC to DC converter 106.

[0070] In one embodiment, the converter controller 126 is configured to control operation of the switching unit 304. More specifically, the converter controller 126 aids in switching the switching unit 304 to selectively couple the first energy storage device 112 and the second energy storage device 114 to the DC link 122 via the energy storage DC to DC converter 302 at different instances of time and ^; or for different time durations. The term‘switching of the switching unit,’ as used herein, refers to activation and/or deactivation of the switching unit.

[0071] One example of operation of the power generation system 300 is explained herein in greater detail with respect to FIG. 3(a). Specifically, FIG. 3(a) is a schematic representation of a timeline 350 of one embodiment of operation of the power generation system of FIG. 3. In one specific example, when the power generation system 300 operates in the islanded mode, the voltage at the DC link 122 may not be maintained at a determined value of voltage by the DC to AC converter 108. Initially (for example, at time t _P =0) the switching unit 304 is activated to couple the second energy storage device 114 to the DC link 122 via the energy storage DC to DC converter 302, as represented at block 352. During a time period 0 to t _q , the second energy storage device 114 is discharged to maintain the voltage at the DC link 122 to a determined value of voltage as depicted at block 354. Further, during the time period 0 to tq, the energy storage DC to DC converter 302 operates in a voltage control mode.

[0072] By the time tq, the second energy storage device 114 may have discharged to a certain threshold and the switching unit 304 may decouple the second energy storage device 114. Subsequently, the switching unit 304 may couple the first energy storage device 1 12 to the DC link 122 via the energy storage DC to DC converter 302, as represented at block 356.

[0073] Additionally, during time period tq to ts, the first energy storage device 112 discharges to provide current to the DC link 122 and to maintain the determined value of voltage at the DC link 122 via the energy storage DC to DC converter, as depicted at block 358. During the time period tq to t _s , the energy storage DC to DC converter 302 continues to operate in the voltage control mode, as represented at block 358. Further, at time ts, the switching unit 304 may decouple the first energy storage device 112, as represented at block 360. During the time period 0 to ts, the first and second energy storage devices 1 12, 114 are configured to efficiently discharge per the requirement to prolong the life of the energy storage devices 1 12, 1 14 in order to maintain the determined value of voltage at the DC link 122.

[0074] Furthermore, the foregoing examples, demonstrations, and process steps such as those that may be performed by the system may be implemented by suitable code on a processor-based system, such as a general-purpose or special-purpose computer. It should also be noted that different implementations of the present technique may perform some or all of the steps described herein in different orders or substantially concurrently, that is, in parallel. Furthermore, the functions may be implemented in a variety of programming languages, including but not limited to C++ or Java. Such code may be stored or adapted for storage on one or more tangible, machine readable media, such as on data repository chips, local or remote hard disks, optical disks (/.<?., CDs or DVDs), memory or other media, which may be accessed by a processor-based system to execute the stored code. Note that the tangible media may include paper or another suitable medium upon which the instructions are printed. For instance, the instructions may be electronically captured via optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in the data repository or memory.

[0075] Various embodiments of a power generation system and a method of operating the power generation system are presented. The systems and methods presented herein facilitates to optimize use of energy storage devices, thereby prolonging life of the energy storage devices. Further, the exemplary method entails extracting maximum energy from each energy storage device. Furthermore, the exemplary method aids in efficiently coupling the energy storage devices to the DC link without changing configuration of an existing power generation system.

[0076] While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention . In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof.