BACKGROUND

[0001] One or more embodiments of the present application relates generally to a power generation system and more particularly relates to a charging sub-system for charging an energy storage device employed in the power generation system.

[0002] Typically, power generation systems such as generators use fuels such as diesel, petrol, and the like to generate an electrical power that can be supplied to local electrical loads. Reducing consumption of the fuels is an ongoing effort in achieving low cost and environment friendly power generation systems. To that end, various hybrid power generation systems are available that use a generator operated by a constant speed engine and some form of renewable energy source. In such hybrid power generation systems, as an amount of power generated by the renewable energy source increases, the power generated by the generators operated by the constant speed engine needs to be reduced. Moreover, certain stand-alone renewable energy source based power generation systems, such as, solar farm or wind farm, are also functional.

[0003] In some configurations, an energy storage device such as a battery is employed in such hybrid or stand-alone renewable energy source based power generation systems to power electronic components of the hybrid power generation system and to store excess electrical power generated by the renewable energy source. Sometimes, one or more electronic components are configured to facilitate the charging of the energy storage device. However, in certain instances, if the energy storage device gets completely discharged due to some fault, the electronic components within the power generation systems may stop functioning.

Consequently, charging of the energy storage device cannot be initiated or continued via the one or more electronic components that are configured to facilitate the charging of the energy storage device.

[0004] In light of the above, there exist a need for an improved system for charging the energy storage device in situations when the energy storage device is completely discharged or unable to power the electronic components of the power generation system. BRIEF DESCRIPTION

[0005] In accordance with an embodiment of the present specification, a charging sub-system is presented. The charging sub-system includes a switch directly connected between the renewable energy based power source and the energy storage device, wherein the switch is configured to electrically couple the renewable energy based power source with the energy storage device to charge the energy storage device.

[0006] In accordance with an embodiment of the present specification, a power generation system is presented. The power generation system includes a back-to-back converter coupled to a generator. The power generation system further includes a renewable energy based power source electrically coupled to the back-to-back converter. Moreover, the power generation system includes a charging sub-system having a switch directly connected between the renewable energy based power source and an energy storage device, wherein the switch is configured to electrically couple the renewable energy based power source with the energy storage device to charge the energy storage device, and wherein the energy storage device is electrically coupled to the back-to-back converter.

[0007] In accordance with an embodiment of the present specification, a power generation system is presented. The power generation system includes a doubly-fed induction generator (DFIG) having a rotor winding and a stator winding. The power generation system further includes a back-to-back converter configured to be coupled to the DFIG. The back-to-back converter includes a rotor-side converter electrically coupled to the rotor winding and a line-side converter electrically coupled to the stator winding, and wherein the rotor-side converter and the line-side converter are electrically coupled to each other via a direct current (DC) link.

Furthermore, the power generation system includes renewable energy based power source electrically coupled to the DC-link of the back-to-back converter. Moreover, the power generation system also includes an energy storage device electrically coupled to the DC-link of the back-to-back converter. Additionally, the power generation system includes a charging subsystem including a switch electrically disposed between the renewable energy based power source and the energy storage device, wherein the switch is configured to electrically couple the renewable energy based power source with the energy storage device to charge the energy storage device.

[0008] In accordance with an embodiment of the present specification, a method for charging an energy storage device is presented. The method includes determining if an energy storage level of the energy storage device is zero or lower than a first predetermined level, wherein the energy storage device is electrically coupled to a back-to-back converter. The method further includes charging the energy storage device using a current from a renewable energy based power source via a charging sub-system if the energy storage level of the energy storage device is zero or lower than the first predetermined level, wherein the charging sub-system includes a switch disposed between the energy storage device and the renewable energy based power source, and wherein the renewable energy based power source is further coupled to the back-to- back converter.

DRAWINGS

[0009] These and other features, aspects, and advantages of the present invention 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:

[0010] FIG. 1 is a block diagram of a power generation system having a charging subsystem, in accordance with one or more embodiments of the present specification;

[0011] FIG. 2 is a block diagram of another power generation system having a charging subsystem, in accordance with one or more embodiments of the present specification;

[0012] FIG. 3 is a block diagram of another power generation system having a charging subsystem, in accordance with one or more embodiments of the present specification;

[0013] FIG. 4 is a block diagram of another power generation system having a charging subsystem, in accordance with one or more embodiments of the present specification;

[0014] FIG. 5 is a block diagram of a doubly-fed induction generator based power generation system having a charging sub-system, in accordance with one or more embodiments of the present specification;

[0015] FIG. 6 is a flowchart of an example method for facilitating charging of an energy storage device, in accordance with one or more embodiments of the present specification;

[0016] FIG. 7 is a flowchart of another example method for facilitating charging of an energy storage device, in accordance with one or more embodiments of the present specification; and

[0017] FIG. 8 is a flowchart of yet another example method for facilitating charging of an energy storage device, in accordance with one or more embodiments of the present specification. DETAILED DESCRIPTION

[0018] The specification may be best understood with reference to the detailed figures and description set forth herein. Various embodiments are described hereinafter with reference to the figures. However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes as the method and the system may extend beyond the described embodiments.

[0019] In the following specification, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. As used herein, the term "or" is not meant to be exclusive and refers to at least one of the referenced components being present and includes instances in which a combination of the referenced components may be present, unless the context clearly dictates otherwise.

[0020] As used herein, the terms "may" and "may be" indicate a possibility of an occurrence within a set of circumstances; a possession of a specified property, characteristic or function; and/or qualify another verb by expressing one or more of an ability, capability, or possibility associated with the qualified verb. Accordingly, usage of "may" and "may be" indicates that a modified term is apparently appropriate, capable, or suitable for an indicated capacity, function, or usage, while taking into account that in some circumstances, the modified term may sometimes not be appropriate, capable, or suitable.

[0021] FIG. 1 is a block diagram of a power generation system (100) having a charging subsystem (102), in accordance with one or more embodiments of the present specification. In some embodiments, the power generation system (100) may include one or more of the charging subsystem (102), an energy storage device (104), a renewable energy based power source (106), a back-to-back converter (108), and a generator (110). The back-to-back converter (108) may be powered by the energy storage device (104).

[0022] In some embodiments, the energy storage device (104) and the renewable energy based power source (106) are electrically coupled to the back-to-back converter (108). The back- to-back converter (108) is electrically coupled to the generator (110). In some embodiments, the charging sub-system (102) is electrically disposed between the renewable energy based power source (106) and the energy storage device (104). The charging sub-system (102) includes a switch (112) configured to electrically couple the renewable energy based power source (106) with the energy storage device (104) to charge the energy storage device (104).

[0023] The energy storage device (104) may include arrangements employing one or more batteries, capacitors, and the like. In some embodiments, the energy storage device (104) may be electrically coupled to the back-to-back converter (108) to supply an energy storage power to the back-to-back converter (108). In some embodiments, the energy storage device (104) may be electrically coupled to the back-to-back converter (108) via a DC-DC converter (not shown in FIG. 1).

[0024] In some embodiments, one or more renewable energy based power sources, such as, the renewable energy based power source (106), for example, a photo-voltaic (PV) power source (see FIGs 4-5) may be electrically coupled to the back-to-back converter (108). The PV power source may include one or more PV arrays (not shown in FIG. 1), where each PV array may include at least one PV module (not shown in FIG. 1). A PV module may include a suitable arrangement of a plurality of PV cells (diodes and/or transistors). The PV power source may generate a DC voltage constituting a solar electrical power that depends on solar insolation, weather conditions, and/or time of the day. Accordingly, the PV power source may be configured to supply the solar electrical power to the back-to-back converter (108). Although in the ongoing description, the PV power source is described as one embodiment of the renewable energy based power source, use of other forms of renewable energy based power sources that are capable of generating and/or supplying DC current is also envisioned within the purview of the present specification. In some embodiments, the renewable energy based power source (106) may be coupled to the back-to-back converter (108) via a DC-DC converter (not shown in FIG.

1).

[0025] In some embodiments, the generator (110) may be operated via a prime mover (not shown in FIG. 1, see FIGs 4-5) and configured to generate AC electrical power, hereinafter referred to as a generator power. The generator (110) is coupled to the back-to-back converter (108) to supply the generator power to the back-to-back converter (108). Various examples of the generator (110) may include but are not limited to, a synchronous generator, an asynchronous generator, or a doubly-fed induction generator (DFIG).

[0026] The back-to-back converter (108) may include a plurality of AC -DC converters (see FIGs. 2-5). The back-to-back converter (108) is configured to receive power from one or more of the generator (110), the renewable energy based power source (106), and/or the energy storage device (104) and generate an output power at an output (114). The output power of the back-to- back converter (108) may be supplied to electrical load (not shown in FIG. 1) coupled to the output (114). In some embodiments, the back-to-back converter (108) may be powered by the energy storage device (104). [0027] In some embodiments, the charging sub-system (102) includes the switch (112) that is capable of electrically connecting or disconnecting one or more electrical systems/ devices coupled to the switch (112) with each other. In the configuration of FIG. 1, the switch (112) is coupled to the energy storage device (104) and the renewable energy based power source (106), and configured to electrically connect or disconnect the renewable energy based power source (106) and the energy storage device (104). In some embodiments, the switch (112) is directly connected between the renewable energy based power source (106) and the energy storage device (104). In some embodiments, the switch (112) is operable electronically. In certain

embodiments, the switch (112) may be operable without using power from the energy storage device (104). In such configurations, the charging sub-system (102) may employ a separate power source, such as, a battery (not shown in FIG. 1) to power the switch (112). In some embodiments, the switch (112) is manually operable. In certain other embodiments, the switch (112) is capable of being operated both manually and electronically.

[0028] In certain embodiments, it may be desirable to charge the energy storage device (104) when a charge stored in the energy storage device is zero or substantially close to zero. Such situation may arise when an uncharged energy storage device (104) is installed in the power generation system (100), or when the energy storage device (104) is discharged below a determined charge level. By way of example, during operation of the system 100, the energy storage device (104) may inadvertently get discharged due to a fault that may result in energy leakage from the energy storage device (104). In certain embodiments, it may be desirable to charge the energy storage device (104) when the charge stored in the energy storage device (104) drops below a first predetermined level. In some embodiments, the first predetermined level may be in a range from 0% to 5% of a maximum charge storage capacity of the energy storage device (104). In some embodiments, the first predetermined level may be in a range from 5% to 10% of a maximum charge storage capacity of the energy storage device (104).

[0029] In certain embodiments, a need to charge the energy storage device (104) may be manually determined. For example, the need to charge the energy storage device (104) may be determined by measuring voltage across positive and negative terminals of the energy storage device (104). In certain embodiments, an energy level of the energy storage device (104) may be determined electronically (see FIGs 2, 3, and 5) using one or more sensors.

[0030] In certain embodiments, if it is determined (manually or electronically) that energy storage device (104) is discharged or the charge stored in the energy storage device (104) is below the first predetermined level, it may be desirable to charge the energy storage device (104). To that end, in some embodiments, the switch (112) may be operated, manually or electronically, to initiate charging of the energy storage device (104). The switch (112) is operated such that the renewable energy based power source (106) is electrically connected to the energy storage device (104). In some embodiments, the switch (112) is operated such that the renewable energy based power source (106) is directly connected to the energy storage device (104) to charge the energy storage device (104) by supplying the auxiliary electrical power to the energy storage device (104).

[0031] Moreover, when the energy storage device (104) is charged at least upto a second predetermined level, charging of the energy storage device (104) may be discontinued via the switch (112). The second predetermined level may be same or different from the first predetermined level. To discontinue the charging of the energy storage device (104), the switch may be operated manually or electronically such the renewable energy based power source (106) is electrically disconnected from the energy storage device (104).

[0032] FIG. 2 is a block diagram of a power generation system (200) having a charging subsystem (202), in accordance with one or more embodiments of the present specification. The power generation system (200) may include a charging sub-system (202), the energy storage device (104), the renewable energy based power source (106), the generator (110), and a back-to- back converter (204). FIG. 2 includes one or more elements as described in FIG. 1.

[0033] The back-to-back converter (204) may be coupled to the generator (110). The back- to-back converter (204) may be representative of one embodiment of the back-to-back converter (108) of FIG. 1. In the configuration of FIG. 2, the back-to-back converter (204) includes a first AC -DC converter (206) and a second AC -DC converter (208). The second AC-DC converter (208) is electrically coupled to the first AC -DC converter (206) via a direct current (DC) link (207). In some embodiments, the renewable energy based power source (106) is electrically coupled to DC-link (207) and supplies auxiliary electrical power to the DC-link (207). The energy storage device (104) is also electrically coupled to the DC-link (207) and configured to supply energy storage power to the DC-link (207). The second AC -DC converter (208) is further electrically coupled to at least one electrical load (not shown) via an output port (209).

[0034] In some embodiments, the first AC -DC converter (206) and/or the second AC -DC converter (208) are configured to convert AC power into DC power. In some embodiments, the first AC -DC converter (206) and/or the second AC -DC converter (208) are configured to convert DC power into AC power. In one embodiment, the first AC -DC converter (206) receives the generator power from the generator (110) and converts the generator power into DC power. The first AC -DC converter (206) supplies the DC power to the DC-link (207). Additionally, in some embodiments, the DC-link (207) also receives DC power from one or both of the renewable energy based power source (106) and the energy storage device (104). The second AC -DC converter (208) converts the DC power from the DC-link (207) into an AC output power which may be supplied to the electrical load (not shown).

[0035] In some embodiments, the renewable energy based power source (106) may be directly connected to the DC-link (207) of the back-to-back converter (204) and configured to supply the auxiliary electrical power to the DC-link (207). In some embodiments, as depicted in FIG. 2, the renewable energy based power source (106) may be electrically coupled to the DC- link (207) via a first DC-DC converter (220). In such embodiments, the auxiliary electrical power may be supplied from the renewable energy based power source (106) to the DC-link (207) via the first DC-DC converter (220). The first DC-DC converter (220) may be operated as a buck converter, a boost converter, or a buck-boost converter.

[0036] The energy storage device (104) may be electrically coupled to the back-to-back converter (204) via a second DC-DC converter (222). The second DC-DC converter (222) may be electrically coupled between the energy storage device (104) and the DC-link (207). The second DC-DC converter (222) may be operated as a buck converter, a boost converter, or a buck-boost converter. In such embodiments, the energy storage power may be supplied from the energy storage device (104) to the DC-link (207) via the second DC-DC converter (222). In certain embodiments, the energy storage device (104) may also be charged via the second DC- DC converter (222) using DC-power from the DC-link (207).

[0037] Additionally, in certain embodiments, the power generation system may also include a third DC-DC converter (not shown in FIG. 2) electrically coupled between the renewable energy based power source (106) and the energy storage device (104). The third DC-DC converter may be configured to charge the third DC-DC converter when desired.

[0038] In some embodiments, the power generation system may also include a central controller (224). The central controller (224) may be electrically coupled to one or more of the first AC -DC converter (206), the second AC-DC converter (208), the first DC-DC converter (220), and the second DC-DC converter (222) to control operations performed by these converters (206, 208, 220, and 222). In some embodiments, the central controller (224) may include a specially programmed general purpose computer, a microprocessor, a digital signal processor, and/or a microcontroller. The central controller (224) may also include input/output ports, and a storage medium, such as, an electronic memory. Various examples of the microprocessor include, but are not limited to, a reduced instruction set computing (RISC) architecture type microprocessor or a complex instruction set computing (CISC) architecture type microprocessor. Further, the microprocessor may be a single-core type or multi-core type.

Alternatively, the central controller (224) may be implemented as hardware elements such as circuit boards with processors or as software running on a processor such as a commercial, off- the-shelf personal computer (PC), or a microcontroller. In certain embodiments, the first AC -DC converter (206), the second AC-DC converters (208), the first DC-DC converter (220), and the second DC-DC converter (222) may include controllers / control units / electronics to control their respective operations under a supervisory control of the central controller (224).

[0039] In some embodiments, the central controller (224) may receive a power supply from the energy storage device (104). Further, in one embodiment, the central controller (224) may receive the power supply from the energy storage device (104) via the second DC-DC converter (222). In another embodiment, the power generation system (200) may include an additional DC-DC converter (not shown in FIG. 2), hereinafter referred to as a "power supply converter," electrically coupled between the central controller (224) and the energy storage device (104). In certain embodiments, the power supply converter is electrically coupled to biasing / power input terminals of the central controller (224). The power supply converter may be operated as buck converter to provide power supply to the central controller (224).

[0040] In certain embodiments, when the energy storage device (104) is discharged below a determined threshold (such as, zero charge) or when the energy storage device (104) does not have sufficient charge to power the central controller (224), the central controller (224) may not function. In some such embodiments, one or more of the first AC -DC converter (206), the second AC -DC converter (208), the first DC-DC converter (220), the second DC-DC converter (222), and/or the third DC-DC converter may stop functioning or may malfunction since the central controller (224) is non-functional. In these embodiments, the energy storage device (104) may be charged to restore functionality of the central controller (224) and devices connected thereto. In certain embodiments, when at least one of the second DC-DC converter (222) and the third DC-DC converter is non-functional, it may not the possible to charge the energy storage device (104) using the non-functional converters (222) and (224). To that end, in some embodiments, the charging sub-system (202) may be disposed between the renewable energy based power source (106) and the energy storage device (104) to facilitate charging of the energy storage device (104). The charging sub-system (202) is configured to electrically couple the renewable energy based power source (106) with the energy storage device (104) to charge the energy storage device (104). [0041] The charging sub-system (202) is coupled between the renewable energy based power source (106) and the energy storage device (104) as depicted in FIG. 2. In certain embodiments, the charging sub-system (202) is directly connected between an output of the renewable energy based power source (106) and terminals of the energy storage device (104). In some

embodiments, the charging sub-system (202) may include one or more of a switch (210), a sensor (212), and a switch controller (214). Moreover, in some embodiments, the charging sub-system (202) may include a power source, such as, a battery (216). The battery (216) may be electrically coupled to one or more of the switch (210), the sensor (212), and the switch controller (214). The battery (216) supplies power to the switch (210), the sensor (212), and the switch controller (214) to facilitate their respective functions.

[0042] The switch (210) may be representative of one embodiment of the switch (112) of FIG. 1. The switch (210) may be coupled between the renewable energy based power source (106) and the energy storage device (104). In certain embodiments, the switch (210) is directly connected between the output of the renewable energy based power source (106) and terminals of the energy storage device (104). The switch (210) is capable of being controlled electronically. In some embodiments, the switch (210) may be a semiconductor switch. Non-limiting examples of the semiconductor switch may include transistors, gate commutated thyristors, field effect transistors, insulated gate bipolar transistors, gate turn-off thyristors, static induction transistors, static induction thyristors, or combinations thereof. Moreover, materials used to form the semiconductor switch may include, but are not limited to, silicon (Si), germanium (Ge), silicon carbide (SiC), gallium nitride (GaN), gallium arsenide (GaAs) or combinations thereof.

[0043] The sensor (212) may be electrically or electromagnetically coupled to the energy storage device (104). Non-limiting examples of the sensor (212) may include a voltage sensor or a current sensor. In some embodiments, the sensor (212) is electrically coupled to one or more terminals of the energy storage device (104). The sensor (212) may be configured to generate an electrical signal indicative of an energy storage level of the energy storage device (104).

[0044] The switch controller (214) may be electrically coupled to the sensor (212). The switch controller (214) is configured to receive the electrical signal indicative of the energy storage level from the sensor (212). In some embodiments, the switch controller (214) may include a specially programmed general purpose computer, a microprocessor, a digital signal processor, and/or a microcontroller. The switch controller (214) may also include input/output ports, and a storage medium, such as, an electronic memory. Various examples of the microprocessor include, but are not limited to, a reduced instruction set computing (RISC) architecture type microprocessor or a complex instruction set computing (CISC) architecture type microprocessor. Further, the microprocessor may be a single-core type or multi-core type.

Alternatively, the switch controller (214) may be implemented as hardware elements such as circuit boards with processors or as software running on a processor such as a commercial, off- the-shelf personal computer (PC), or a microcontroller. In certain embodiments, the switch controller (214) may be implemented using logic gates, decoders, analog to digital converters, Op- Amp, or combinations thereof. In some embodiments, the switch controller (214) may be capable of executing program instructions for controlling charging of the energy storage device (104).

[0045] In some embodiments, the switch controller (214) may be configured to determine whether the energy storage level of the energy storage device (104) is zero or lower than the first predetermined level. In some embodiments, the first predetermined level may be in a range from 0% to 5% of a maximum charge storage capacity of the energy storage device (104). In some embodiments, the first predetermined level may be in a range from 5% to 10% of a maximum charge storage capacity of the energy storage device (104). In some embodiments, the first predetermined level may be similar to an energy required to supply power to the central controller (224) such that the central controller (224) is configured to control one or more devices connected thereto. The switch controller (214) may determine whether the energy storage level of the energy storage device (104) is zero or lower than the first predetermined level based on one or more parameters of the electrical signal received from the sensor (212). Such parameters of the electrical signal include a magnitude, a frequency, a phase, or combinations thereof.

[0046] In some embodiments, the switch controller (214) is also configured to determine whether the energy storage device (104) is charged to the second predetermined level based on the one or more parameters of the electrical signal received from the sensor (212). In one embodiment, the second predetermined level may be similar to a maximum charge storage capacity of the energy storage device (104). In some embodiments, the second predetermined level may be in a range of 70% to 99.99% of the maximum charge storage capacity of the energy storage device (104). In certain embodiments, the second predetermined level may be similar to the energy required to supply power to the central controller (224) such that central controller (224) is operable control one or more devices connected thereto.

[0047] The switch controller (214) may be electrically connected to the switch (210). In some embodiments, the switch controller (214) may be electrically connected to a control terminal (not shown in FIG. 2) of the switch (210). For example, the control terminal may be a gate terminal of the switch (210). When it is determined by the switch controller (214) that the energy storage level of the energy storage device (104) is zero or lower than the first

predetermined level, the switch controller (214) is configured to control switching of the switch (210). By way of example, when it is determined by the switch controller (214) that the energy storage level of the energy storage device is zero or substantially close to zero, the switch controller (214) may send a control signal to the switch (210) to transition the switch (210) to an activated or ON-state from a deactivated or OFF-state. When the switch (210) is in the ON-state, an electrical connection between the renewable energy based power source (106) and the energy storage device (104) is established. Consequently, a charging current flows from the renewable energy based power source (106) to the energy storage device (104) to charge the energy storage device (104). In some embodiments, when the switch (210) is in the ON-state the renewable energy based power source (106) may be directly connected to the energy storage device (104) to facilitate charging of the energy storage device (104).

[0048] In certain embodiments, when it is determined that the energy storage device (104) is charged to the second predetermined level, the switch controller (214) may send another control signal to the switch (210) to transition the switch (210) to the OFF-state. When the switch (210) is in the OFF-state, the renewable energy based power source (106) may be electrically decoupled from the energy storage device (104). Consequently, charging of the energy storage device (104) via the switch (210) may be discontinued.

[0049] FIG. 3 is a block diagram of a power generation system (300) having a charging subsystem (302), in accordance with one or more embodiments of the present specification. FIG. 3 includes one or more elements as described in FIGs. 1 and 2.

[0050] In certain embodiments, the charging sub-system (302) of FIG. 3 is configured to inform a user or an operator of the power generation system (300) about a need for initiating or discontinuing charging of the energy storage device (104). Accordingly, in some embodiments, in comparison to the charging sub-system (202) of FIG. 2, the charging sub-system (302) additionally includes one or more notification devices, such as, a notification device (304).

Moreover, the charging sub-system (302) also includes a switch (306) which is manually controllable in comparison to the electronically controllable switch (210) of FIG. 1. In some embodiments, the switch (306) is directly connected between the renewable energy based power source (106) and the energy storage device (104). The battery (216) may be electrically coupled to the sensor (212), the switch controller (214), and the notification device (304). [0051] The notification device (304) may include a hardware and/or software for issuing an alert to the user / operator of the power generation system (300). The alert may include an audio alert, a visual alert, a wireless communication alert, or combinations thereof. Non-limiting examples of the audio alert include a beep sound, a pre-selected audio message, or siren sound, and the like. Non-limiting examples of the visual alert may include glowing of a light, display of a message or a video, and the like. Non-limiting examples of the wireless communication alert may include, communicating a text message and/or a call to the user/operator of the power generation system (300).

[0052] The notification device (304) may be electrically connected to the switch controller (214). In some embodiments, the notification device (304) may be operated by the switch controller (214) to generate the alert for the user/operator of the power generation system (300) regarding operating condition of the energy storage device (104). In one embodiment, the operating condition of the energy storage device (104) may be indicative of the energy storage level of the energy storage device (104) being zero or lower than the first predetermined level. In such an instance, the switch controller (214) may control operation of the notification device (304) to generate a first alert indicative of a need to charge the energy storage device (104). Based on the first alert, the user/operator may turn-on the switch (306) to operate the switch (306) in ON-state, thereby initiating charging of the energy storage device (104).

[0053] In some embodiments, the operating condition of the energy storage device (104) may be indicative of a need to discontinue charging of the energy storage device (104). In such an instance, the switch controller (214) may control the notification device (304) to generate a second alert indicative of a need to discontinue charging of the energy storage device (104). The second alert may be different from the first alert. Based on the second alert, the user / operator may turn-off the switch (306) to operate the switch (210) in OFF-state, such that the charging of the energy storage device (104) is stopped.

[0054] FIG. 4 is a block diagram of another power generation system (400) having a charging sub-system (402), in accordance with one or more embodiments of the present specification. FIG. 4 includes one or more elements as described in FIGs. 1 and 2, description of which is not repeated herein.

[0055] The charging sub-system (402) may be representative of one embodiment of the charging sub-system (102) of FIG. 1. The charging sub-system (402) may be coupled between the renewable energy based power source (106) and the energy storage device (104) as depicted in FIG. 4. In comparison to FIG. 2, the charging sub-system (402) of FIG. 4 does not include the switch controller (214). The switch (210), the sensor (212), and the battery (216) may be coupled to the central controller (224). In certain embodiments, the central controller (224) may also be powered by the battery (216). Further, the central controller (224) may be configured to perform functionalities performed by the switch controller (214). More particularly, the central controller (224) may be configured to charge the energy storage device (104) based on the electrical signal received from the sensor (212).

[0056] The central controller (224) may be configured to determine whether the energy storage level of the energy storage device (104) is zero or lower than the first predetermined level. When it is determined by the central controller (224) that the energy storage level of the energy storage device is zero or lower than the first predetermined level, the central controller (224) may send a control signal to the switch (210) to transition the switch (210) in ON-state. When the switch (210) operates in the ON-state, an electrical connection between the renewable energy based power source (106) and the energy storage device (104) is established.

Accordingly, a charging current flows from the renewable energy based power source (106) to the energy storage device (104) to charge the energy storage device (104).

[0057] In certain embodiments, the central controller (224) may be configured to determine whether the energy storage device (104) has charged at least up-to the second predetermined level. When it is determined that the energy storage device (104) is charged to at least up-to the second predetermined level, the central controller (224) may send another control signal to the switch (210) to transition the switch (210) in the OFF-state. When the switch (210) operates in the OFF-state, the renewable energy based power source (106) is disconnected from the energy storage device (104). Consequently, charging of the energy storage device (104) may be stopped.

[0058] FIG. 5 is a block diagram of a doubly-fed induction generator (DFIG) based power generation system (500) having a charging sub-system (502), in accordance with one or more embodiments of the present specification. In some embodiments, the power generation system (500) may include a prime mover (504), a DFIG (506), a back-to-back converter (508), a renewable energy based power source (106), the energy storage device (104), and a central controller (224).

[0059] The prime mover (504) refers to any system that may impart a rotational motion to rotary element(s) (e.g., a rotor) of the DFIG (506). Non-limiting examples of the prime mover (504) may include an engine that may be operable at variable speeds, a gas turbine, a wind turbine, a compressor, or combinations thereof. As used herein, the prime mover (504) is described as the engine capable of being operated at variable speeds. The engine (504) may be an internal combustion engine, an operating speed of which may be varied by the central controller (224). More particularly, the engine (504) may be a variable speed reciprocating engine, where the reciprocating motion of a piston is translated into a rotational speed of a crank shaft connected thereto. The engine (504) may be operated by combustion of various fuels including, but not limited to, diesel, natural gas, petrol, liquefied petroleum gas (LPG), biogas, biomass, producer gas, and the like. The engine (504) may also be operated using waste heat cycle. It is to be noted that the scope of the present specification is not limited by the types of fuel and the engine (504) employed in the power generation system (500).

[0060] The DFIG (506) may include a stator (510), a rotor (512), a stator winding (514) disposed on the stator (510), and a rotor winding (516) disposed on the rotor (512). In the DFIG (506), the stator winding (514) and the rotor winding (516) are accessible to facilitate external electrical connections. In some embodiments, both the stator winding (514) and the rotor winding (516) may be multi-phase winding, such as a three-phase winding.

[0061] The DFIG (506) may be mechanically coupled to the engine (504). In some embodiments, the rotor (512) of the DFIG (506) may be mechanically coupled to the crank shaft of the engine (504), such that during operation, rotations of the crank shaft may cause a rotary motion of the rotor (512) of the DFIG (506). In some embodiments, the crank shaft of the engine (504) may be coupled to the rotor (512) of the DFIG (506) through one or more gears. In operation, the DFIG (506) may be configured to generate electrical power, hereinafter referred to as a stator power, at the stator winding (514). Moreover, the DFIG (506) may be configured to generate or absorb additional electrical power, hereafter referred to as a rotor power, at the rotor winding (516) depending on an operating speed (co) of the engine (504).

[0062] The back-to-back converter (508) may include a rotor-side converter (518), a line-side converter (520). The rotor-side converter (518) may be representative of one embodiment of the first AC -DC converter (206) of FIG. 2. The line-side converter (520) may be representative of one embodiment of the second AC -DC converter (208) of FIG.2. The rotor-side converter (518) may be electrically coupled to the rotor winding (516) of the DFIG (506). Further, the line-side converter (520) may be electrically coupled to the stator winding (514) of the DFIG (506). In one embodiment, the rotor-side converter (518) and the line-side converter (520) are also coupled to each other. For example, the rotor-side converter (518) is coupled to the line-side converter (520) via a direct-current (DC) link (524). [0063] In some embodiments, the renewable energy based power source (106) is electrically coupled to the back-to-back converter (508) at the DC-link (524). In some embodiments, the renewable energy based power source (106) may be electrically coupled to the back-to-back converter (508) at the DC-link (524) via the first DC-DC converter (220). In some embodiments, the energy storage device (104) may be electrically coupled to the back-to-back converter (508) at the DC-link (524) to supply an energy storage power to the DC-link (524). In some embodiments, the energy storage device (104) may be electrically coupled to the back-to-back converter (508) at the DC-link (524) via the second DC-DC converter (222).

[0064] Additionally, in certain embodiments, the power generation system (500) may also include a third DC-DC converter (not shown) electrically coupled between the renewable energy based power source (106) and the energy storage device (104). The third DC-DC converter may be configured to charge the third DC-DC converter when desired.

[0065] The central controller (224) may be electrically coupled to one or more of the rotor- side converter (518), the line-side converter (520), the first DC-DC converter (220), the second DC-DC converter (222), and the third DC-DC converter to control operations performed by them. In certain embodiments, the rotor-side converter (518), the line-side converter (520), the first DC-DC converter (220), the second DC-DC converter (222), and the third DC-DC converter may include controllers / control units / electronics to control their respective operations under a supervisory control of the central controller (224).

[0066] The charging sub-system (502) may be coupled between the renewable energy based power source (106) and the energy storage device (104) as depicted in FIG. 5. In certain embodiments, the charging sub-system (502) is coupled directly between an output of the renewable energy based power source (106) and the energy storage device (104). In some embodiments, the charging sub-system (502) may include a switch electrically disposed between the renewable energy based power source (106) and the energy storage device (104), where the switch is configured to electrically couple the renewable energy based power source (106) with the energy storage device (104) to charge the energy storage device.

[0067] In one embodiment, the charging sub-system (502) may be similar to the charging sub-system (102) of FIG. 1 having a switch (112) coupled between the renewable energy based power source (106) and the energy storage device (104).

[0068] In another embodiment, the charging sub-system (502) may be similar to the charging sub-system (202) of FIG. 2 and disposed in the power generation system (500) in a similar fashion as shown FIG. 2. Accordingly, charging sub-system (502) may also include the switch (210), the sensor (212), the switch controller (214), and the battery (216) arranged as shown in FIG. 2. The sensor (212) generates an electrical signal indicative of an energy storage level of the energy storage device (104). Further, the switch controller (214) is configured to receive the electrical signal the sensor. The switch controller (214) is further configured to determine whether the energy storage level of the energy storage device (104) is zero or lower than the first predetermined level. In such a configuration, charging of the energy storage device (104) is electronically controlled by the switch controller (214). For example, to initiate the charging of the energy storage device (104), the switch controller (214) may be configured to send a control signal to the switch (210) such that the switch (210) is transitioned to the ON-state if it is determined by the switch controller (214) that the energy storage level is zero or lower than the first predetermined level. Moreover, in certain embodiments, to discontinue the charging of the energy storage device (104), the switch controller (214) may be configured to send another control signal to the switch (210) to facilitate transition of the switch (210) to the OFF-state, if it is determined by the switch controller (214) that the energy storage level is greater than a second predetermined level.

[0069] In another embodiment, the charging sub-system (502) may be similar to the charging sub-system (302) of FIG. 3 and disposed in the power generation system (500) in a similar fashion as shown FIG. 3. In such a configuration, the charging sub-system (502) includes the notification device (304), the switch (306), the switch controller (214), the sensor (212), and the battery (216) arranged as shown in FIG. 3. A user/operator of the power generation system (500) may be alerted using the notification device (304). The notification device (304) is electrically coupled to the switch controller (214) and configured to generate an alert if it is determined by the switch controller (214) that the energy storage level of the energy storage level of the energy storage device (104) is zero or lower than the first predetermined level. Further, the charging of the energy storage device (104) is manually controlled by a user/operator of the power generation system (500) based on an alert communicated by the notification device (304).

[0070] In yet another embodiment, the charging sub-system (502) may be similar to the charging sub-system (402) of FIG. 4 and disposed in the power generation system (500) in a similar fashion as shown FIG. 4. Accordingly, the charging sub-system (502) may also include the switch (210), the sensor (212), the battery (216) arranged as shown in FIG. 2. More particularly, the sensor (212) may be electrically coupled to the central controller (224). Also, the central controller (224) is electrically coupled to the switch (210). In such a configuration, charging of the energy storage device (104) is electronically controlled by the central controller

(224) based on the electrical signal received from the sensor (212). [0071] The sensor (212) generates an electrical signal indicative of an energy storage level of the energy storage device (104). Further, the central controller (224) is configured to receive the electrical signal the sensor (212). The central controller (224) is further configured to determine whether the energy storage level of the energy storage device (104) is zero or lower than the first predetermined level. In such a configuration, charging of the energy storage device (104) is electronically controlled by the central controller (224). For example, to initiate the charging of the energy storage device (104), the central controller (224) may be configured to send a control signal to the switch (210) such that the switch (210) is transitioned to the ON-state if it is determined by the central controller (224) that the energy storage level is zero or lower than the first predetermined level. Moreover, in certain embodiments, to discontinue the charging of the energy storage device (104), the central controller (224) may be configured to send another control signal to the switch (210) such that the switch (210) is transitioned to OFF-state if it is determined by the central controller (224) that the energy storage level is greater than the second predetermined level.

[0072] FIG. 6 is a flowchart (600) of an example method for facilitating charging of an energy storage device, such as the energy storage device (104), in accordance with one or more embodiments of the present specification. The method of FIG. 6, may be performed by one more of the power generation systems described in FIGs. 1-5. Accordingly, the method of FIG. 6 is described with reference to FIGs. 1-5.

[0073] At block (602), it is determined whether an energy storage level of the energy storage device (104) is zero or lower than a first predetermined level. In some embodiments, the energy storage level of the energy storage device (104) being zero or lower than the first predetermined level may be determined manually, as described in FIG.1. in some embodiments, the energy storage level of the energy storage device (104) being zero or lower than the first predetermined level may be electronically determined by the switch controller (214), for example, as described in FIGs. 2-3 or by the central controller (224), for example, as described in FIG. 4.

[0074] Further, at block (604), the energy storage device (104) may be charged using a current from a renewable energy based power source, such as the renewable energy based power source (106) via a charging sub-system, for example, the charging sub-system (102, 202, 302, 402, or 502), if the energy storage level of the energy storage device is zero or lower than the first predetermined level. In some embodiments, the energy storage device (104) may be charged by manually operating a switch, such as the switch (112 or 306). In certain embodiments, a switch such as the switch (112 or 210) may be electronically operated to charge the energy storage device (104).

[0075] FIG. 7 is a flowchart (700) of another example method for facilitating charging of an energy storage device, such as the energy storage device (104), in accordance with one or more embodiments of the present specification. More particularly, the flowchart (700) represents a method for facilitating charging of the energy storage device (104) via an electronic control by a charging sub-system, such as the charging sub-system (202, 402, 502) of FIGs. 2, 4, and 5.

Accordingly, the method of FIG. 7 is described with reference to FIGs. 2, 4, and 5. The method of FIG. 7 includes blocks (704-706). In the configuration of FIG. 2, the switch controller (214) facilitates execution of the method steps of blocks (702-706). In the configuration of FIG. 4, the central controller (224) facilitates execution of the method steps of blocks 704-706. In the configuration of FIG. 5, in some embodiments, the central controller (224) facilitates execution of the method steps of blocks (702-706). In the configuration of FIG. 5, in some embodiments, the switch controller (214) facilitates execution of the method steps of blocks (702-706).

[0076] At block (702), an electrical signal indicative of an energy storage level of the energy storage device (104) may be received from a sensor, such as, the sensor (212). Further, at block (704), it is determined whether an energy storage level of the energy storage device (104) is zero or lower than a first predetermined level. The energy storage level of the energy storage device (104) being zero or lower than the first predetermined level may be described by comparing the energy storage level with zero or with the first predetermined level.

[0077] Furthermore, if it is determined by the switch controller (214) or the central controller (224) that the energy storage level of the energy storage device (104) is zero or lower than the first predetermined level, at block (706), charging of the energy storage device (104) may be initiated. The energy storage device (104) may be charged using a power from the renewable energy based power source (106). In some embodiments, the charging the energy storage device (104) includes electronically controlling switching of a switch, such as the switch (210) to initiate the charging of the energy storage device (104) based on the energy storage level of the energy storage device (104). In the configuration of charging sub-system (202) the switching of the switch (210) may be controlled by the switch controller (214). In the configuration of charging sub-system (402) the switching of the switch (210) may be controlled by the central controller (224). To charge the energy storage device (104) using the power from the renewable energy based power source (106) the switch (210) may be transitioned to ON-state. [0078] FIG. 8 is a flowchart of another example method for facilitating charging of an energy storage device, such as the energy storage device (104), in accordance with one or more embodiments of the present specification. More particularly, the flowchart (800) represents a method for facilitating manual charging of the energy storage device (104) using a charging subsystem, such as the charging sub-system (302) of FIG. 3 or the charging sub-system (502) of FIG. 5, in some embodiments. Accordingly, the method of FIG. 8 is described with reference to FIGs. 3 and 5. The method of FIG. 8 includes blocks (802-808). In the configurations of FIGs. 3 and 5, in some embodiments, the switch controller (214) may facilitate execution of the method steps of blocks 802-806. The steps of block 808 may be manually performed. Method steps of the blocks (802) and (804) are similar to blocks (702) and (704), respectively, of FIG. 7.

Accordingly, the corresponding description is not repeated herein.

[0079] At block (806), an alert may be generated. For example, the alert may be generated by a notification device, such as, the notification device (304) of the charging sub-system (302). To facilitate the generation of the alert, the switch controller (214) may send a control signal to the notification device (304) if the energy storage level of the energy storage device (104) is zero or lower than the first predetermined level. The alert may include the audio alert, the visual alert, the wireless communication alert, or combinations thereof.

[0080] Moreover, at block (808), charging of the energy storage device (104) may be initiated. The charging of the energy storage device (104) may be initiated based on the alert generated by the notification device (304). The energy storage device (104) may be charged using a power from the renewable energy based power source (106). In some embodiments, the charging the energy storage device (104) includes manually controlling switching of a switch, such as the switch (306) to initiate the charging of the energy storage device (104) based on the alert. In the configuration of charging sub-system (302) the switching of the switch (306) may be controlled by an operator or user. To charge the energy storage device (104) using the power from the renewable energy based power source (106) the switch (210) may be transitioned to ON-state by the operator or user.

[0081] Any of the foregoing method blocks and/or system elements may be suitably replaced, reordered, or removed, and additional blocks and/or system elements may be inserted, depending on the needs of a particular application, and that the systems of the foregoing embodiments may be implemented using a wide variety of suitable processes and system elements and are not limited to any particular computer hardware, software, middleware, firmware, microcode, etc. [0082] Furthermore, in some embodiments, one of more of the foregoing examples, demonstrations, and method blocks may be implemented by suitable code on a processor-based system, such as a general-purpose or special-purpose computer. Different implementations of the systems and methods may perform some or all of the blocks described herein in different orders, parallel, or substantially concurrently. 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 or non-transitory computer readable media, such as on data repository chips, local or remote hard disks, optical disks (that is, 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.

[0083] Systems and methods, in accordance with one or more embodiments, facilitates charging of the energy storage device (104) even when the energy storage device (104) is completely discharged. In one embodiment, it may be achieved by controlling the charging of the energy storage device (104) by manually operating the switch (112 or 306) in a charging subsystem (102 or 302). In one embodiment, it may be achieved by controlling charging of the energy storage device (104) by electronically operating the switch (112 or 210) in the charging sub-system (102, 202, or 402) via the switch controller (214) or the central controller (224), where the switch controller (214) or the central controller (224) may be operated via a different battery (216). By facilitating charging of the energy storage device (104) in accordance with one or more embodiments, downtime of the power generation system may be reduced. In addition, reliability of the power generation system is also improved.

[0084] The present specification has been described in terms of some specific embodiments. They are intended for illustration only, and should not be construed as being limiting in any way. Thus, it should be understood that modifications can be made thereto, which are within the scope of the present specification and the appended claims.

[0085] It will be appreciated that variants of the above disclosed and other features and functions, or alternatives thereof, may be combined to create many other different systems or applications. Various unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art and are also intended to be encompassed by the following claims.