WO2019177748A1

WO2019177748A1 - A power generation system and a method for operating the same

Info

Publication number: WO2019177748A1
Application number: PCT/US2019/018385
Authority: WO
Inventors: Kasi Viswanadha Raju Gadiraju; Hridya ITTAMVEETTIL; Sumeet Singh Thakur
Original assignee: General Electric Company
Priority date: 2018-03-12
Filing date: 2019-02-18
Publication date: 2019-09-19

Abstract

A method for operating a power generation (100, 200) system is presented. The method includes detecting a failure associated with a line-side converter (108). The method further includes altering, in response to the detected failure, one or more of an operating speed of a rotor (136) of a doubly-fed induction generator (DFIG) (104) and an output power of a prime mover (102, 202) based on a power demand at a point of common coupling (PCC) (120) and a level of an electrical power at a direct current (DC)-link such that an electrical power to meet the power demand at the PCC (120) is supplied via a stator winding (130) of the DFIG to the PCC (120).

Description

A POWER GENERATION SYSTEM AND A METHOD FOR OPERATING THE SAME

BACKGROUND

[0001] Embodiments of the present specification generally relate to a power generation system and in particular, to a method and a control sub-system for controlling operation of the power generation system when a failure associated with a line-side converter is detected.

[0002] Some traditional hybrid power generation systems employ a DFIG, a prime mover and an auxiliary power source (e.g., photovoltaic (PV) power source). In some configurations of a traditional power generation system, the auxiliary power source is coupled to the DFIG via one or more power converter(s). Moreover, the DFIG is also coupled to electric grid or one or more electrical loads via a line-side converter. During operation of the power generation system, electrical power may be generated by one or both of the DFIG and the auxiliary power source. The electrical power thus generated may be supplied to electrical loads and/or an electric grid coupled to the power generation system.

[0003] In some traditional hybrid power generation systems operating in an islanded mode (i.e., when not connected to the electric grid), the line-side converter controls a frequency and/or voltage of electricity generated by the traditional hybrid power generation systems. During operation of such traditional hybrid power generation system, when a fault occurs with the line-side converter or protective devices associated with the line-side converter, the traditional hybrid system is typically disconnected from the electrical loads. Consequently, the supply of electrical power to the electrical loads is interrupted. Further, when the traditional hybrid system is disconnected or shutdown due to the fault associated with the line-side converter or the corresponding protective devices, the electrical power generated by the auxiliary power source is wasted. Moreover, when such traditional hybrid systems are used in remote locations and the fault occurs with the line-side converter or the protective devices associated with the line-side converter, replacing these components or addressing the fault also remains challenging and time-consuming task.

BRIEF DESCRIPTION

[0004] In accordance with one embodiment of the present specification, a method for operating a power generation system is presented. The power generation system includes a prime mover, a doubly -fed induction generator (DFIG), a generator- side converter, a line-side converter coupled to the generator-side converter via a direct current (DC)-link, an energy storage device coupled to the DC-link to supply an electrical power to the DC-link, and a point of common coupling (PCC) at which windings from a stator of the DFIG are coupled to the line-side converter. The method includes detecting a failure associated with the line-side converter. The method further includes altering, in response to the detected failure, one or more of an operating speed of a rotor of the DFIG and an output power of the prime mover based on a power demand at the PCC and a level of the electrical power at the DC-link such that an electrical power to meet the power demand at the PCC is supplied via a stator winding of the DFIG to the PCC.

[0005] In accordance with one embodiment of the present specification, a control sub- system for operating a power generation system is presented. The power generation system includes a prime mover, a DFIG, a generator-side converter, a line-side converter coupled to the generator-side converter via a DC-link, an auxiliary power source and/or an energy storage device coupled to the DC-link to supply an electrical power to the DC-link, and a PCC at which windings from a stator of the DFIG are coupled to the line-side converter. The control sub system includes one or more sensors configured to generate electrical signals. The control sub system further includes a controller operatively coupled to the prime mover, the line-side converter, the generator- side converter, and the one or more sensors. The controller is configured to detect the failure associated with the line-side converter based on the electrical signals generated by the one or more sensors. The controller is further configured to alter, in response to the detection of the failure associated with the line-side converter, one or more of an operating speed of a rotor of the DFIG and an output power of the prime mover based on a power demand at the PCC and a level of electrical power at the DC-link such that an electrical power to meet the power demand at the PCC is supplied via the stator winding to the PCC.

[0006] In accordance with one embodiment of the present specification, a power generation system is presented. The power generation system includes a variable speed engine. Further, the power generation system includes a DFIG mechanically coupled to the variable speed engine, wherein the DFIG includes a stator winding disposed on the stator and a rotor winding disposed on a rotor, wherein the stator winding is electrically coupled to a PCC. Furthermore, the power generation system includes a generator- side converter electrically coupled to the rotor winding. The power generation system also includes a line-side converter electrically coupled to the PCC, wherein the line-side converter is electrically coupled to the generator- side converter via a DC-link. Moreover, the power generation system includes an auxiliary power source and an energy storage device coupled to the DC-link to supply an electrical power to the DC-link. Additionally, the power generation system includes control sub-system operatively coupled to the variable speed engine, the line-side converter, and the generator- side converter. The control sub-system includes one or more sensors configured to generate electrical signals. The control sub-system further includes a controller operatively coupled to the prime mover, the line-side converter, the generator- side converter, and the one or more sensors. The controller is configured to detect the failure associated with the line-side converter based on the electrical signals generated by the one or more sensors. The controller is further configured to alter, in response to the detection of the failure associated with the line-side converter, one or more of an operating speed of a rotor of the DFIG and an output power of the prime mover based on a power demand at the PCC and a level of electrical power at the DC- link such that an electrical power to meet the power demand at the PCC is supplied via the stator winding to the PCC.

DRAWINGS

[0007] These and other features, aspects, and advantages of the present specification 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. l is a block diagram representation of a power generation system, in accordance with one embodiment of the present specification;

[0009] FIG. 2 is a block diagram representation of a power generation system, in accordance with one embodiment of the present specification;

[0010] FIG. 3 is a flow diagram of a method for operating the power generation system of FIG. 1 or FIG. 2, in accordance with one embodiment of the present specification;

[0011] FIGs. 4A, 4B, and 4C represent a flow diagram of a detailed method for operating the power generation system of FIG. 1 or FIG. 2, in accordance with one embodiment of the present specification; and

[0012] FIGs. 5A, 5B, and 5C depict graphical representations showing various power levels and operating speed of a rotor of a DFIG in the power generation systems of FIGs. 1-2, in accordance with one embodiment of the present specification.

DETAILED DESCRIPTION

[0013] In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions may be made to achieve the developer’s specific goals such as compliance with system-related and business-related constraints. [0014] When describing elements of the various embodiments of the present specification, the articles“a”,“an”, and“the” are intended to mean that there are one or more of the elements. The terms“comprising”,“including” and“having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0015] 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.

[0016] In accordance with some embodiments of the present specification, a power generation system is presented. The power generation system includes a variable speed engine. Further, the power generation system includes a DFIG mechanically coupled to the variable speed engine, wherein the DFIG includes a stator winding disposed on the stator and a rotor winding disposed on a rotor, wherein the stator winding is electrically coupled to a PCC. Furthermore, the power generation system includes a generator-side converter electrically coupled to the rotor winding. The power generation system also includes a line-side converter electrically coupled to the PCC, wherein the line-side converter is electrically coupled to the generator- side converter via a DC-link. Moreover, the power generation system includes an auxiliary power source and an energy storage device coupled to the DC-link to supply an electrical power to the DC-link.

[0017] Additionally, the power generation system includes control sub-system operatively coupled to the variable speed engine, the line-side converter, and the generator- side converter. The control sub-system includes one or more sensors configured to generate electrical signals. The control sub-system further includes a controller operatively coupled to the prime mover, the line-side converter, the generator-side converter, and the one or more sensors.

[0018] The controller is configured to detect the failure associated with the line-side converter based on the electrical signals generated by the one or more sensors. The controller is further configured to alter, in response to the detection of the failure associated with the line- side converter, one or more of an operating speed of a rotor of the DFIG and an output power of the prime mover based on a power demand at the PCC and a level of electrical power at the DC-link such that an electrical power to meet the power demand at the PCC is supplied via the stator winding to the PCC. [0019] FIG. 1 is a block diagram representation of a power generation system 100, in accordance with one embodiment of the present specification. The power generation system 100 includes a prime mover 102, a doubly-fed induction generator (DFIG) 104, a generator- side converter 106, a line-side converter 108, a direct current (DC) link 110, a control sub- system 116 and one or both of an auxiliary power source 112 or an energy storage device 114. The power generation system 100 may be configured to generate an alternating current (AC) electrical power which may be accessible from an output power port 118 of the power generation system 100.

[0020] In some embodiments, the output power port 118 of the power generation system 100 may be connected to an electric grid (not shown). The power generation system 100 when connected to the electric grid is also referred to as a grid connected power generation system. The electric grid may be representative of an interconnected network of electrical power sources, electrical power processing systems, and an electrical power distribution system for delivering a grid power (e.g., electricity) from one or more power generation stations to consumers through high/medium voltage transmission lines. By way of example, the electric grid may be a utility power grid, a micro grid, or a mini grid. The term“micro-grid,” as used herein refers to a power generation and supply system that is capable of supplying electrical power of less than 10 kW. The term“mini -grid,” as used herein refers to a power generation and supply system that is capable of supplying electrical power of 10 kW and above.

[0021] In some embodiments, the power generation system 100 is an islanded power generation system, sometimes also referred to as an isolated power generation system which not connected to the electric grid. By way of example, the islanded power generation system may be deployed where connection to the electric grid is not desired or the electric grid is not available. In such a configuration, the output power port 118 of the power generation system 100 may be coupled to an electrical load (not shown). The electrical load may include one or more devices/equipment that consume electricity.

[0022] As depicted in FIG. 1, the DFIG 104 is mechanically coupled to the prime mover 102. The DFIG 104 is also electrically coupled to a point of common coupling PCC 120 via a link 122 and to the generator- side converter 106 via a link 124. The line-side converter 108 may be electrically coupled to the PCC 120 via a link 126. In some embodiments, the line-side converter 108 is electrically coupled to the PCC 120 via the link 126 through a transformer (not shown). Each of the links 122, 124, and 126 may be a multi -phase link, for example, a three- phase electrical link as shown in FIG. 1. The PCC 120 may be connected to the output power port 118 of the power generation system 100. In some embodiments, the power generation system 100 may optionally include a transformer 128 connected between the PCC 120 and the output power port 118.

[0023] The prime mover 102 is coupled to the DFIG 104 and configured to operate the DFIG 104. In particular, the prime mover 102 may be configured to aid in imparting a rotational motion to a rotary element (e.g., a rotor) of the DFIG 104. The prime mover 102 may be an internal combustion engine or an external combustion engine. Non-limiting examples of the internal combustion engine that may be used as the prime mover 102 may include a reciprocating engine such as a diesel engine or a petrol engine, or a rotary engine such as a compressor or a gas turbine. Moreover, the prime mover 102 may be operated by combustion of various fuels including, but not limited to, diesel, natural gas, petrol, liquefied petroleum gas (LPG), liquefied natural gas (LNG), biogas, producer gas, and the like. The prime mover 102 may also be operated using waste heat cycle. It is to be noted that the scope of the present specification is not limited with respect to the types of fuel and the prime mover 102 employed in the power generation system 100. In certain other embodiments, the prime mover 102 may be a wind-turbine. Another non-limiting example of the prime mover 102 may include a hydro turbine.

[0024] The DFIG 104 includes a stator winding 130 and a rotor winding 132. The stator winding 130 may be wound on a stator 134. The rotor winding 132 may be wound on a rotor 136. In some embodiments, both the stator winding 130 and the rotor winding 132 may be multi -phase windings such as a three-phase winding. The DFIG 104 is mechanically coupled to the prime mover 102 and is operable via the prime mover 102. For example, the rotor 136 of the DFIG 104 is mechanically coupled to the rotor (e.g., a crank shaft or a wind turbine rotor) of the prime mover 102 via a shaft 138 such that a rotation of the shaft 138 causes a rotation of the rotor 136 of the DFIG 104.

[0025] During an operation of the power generation system 100, the rotor 136 of the DFIG 104 is operated at a rotational speed which may be a synchronous speed, a sub-synchronous speed, or a super-synchronous speed depending on a rotational speed of the rotor 136 of the DFIG 104. The rotational speed of the rotor 136 is also hereinafter referred to as an operating speed {Nr) of the rotor 136 or the operating speed (Mr) of the DFIG 104. In one example, the synchronous speed may be defined using equation (1).

120 * F

N. = Equation (1)

P

[0026] In equation (1), N_s represents the synchronous speed of the rotor 136, p represents number poles in the rotor 136, and F represents a frequency of a stator voltage (i.e., voltage at the stator winding 130). Accordingly, a sub-synchronous speed of the rotor 136 is defined as a speed that is lower than the synchronous speed of the rotor 136. Therefore, when the operating speed (Nr) of the rotor 136 is sub- synchronous speed, the DFIG 104 is considered to be operated in a sub-synchronous mode. Similarly, a super-synchronous speed of the rotor 136 is defined as a speed that is higher than the synchronous speed of the rotor 136. Accordingly, when the operating speed (Nr) of the rotor 136 is the super-synchronous speed, the DFIG 104 is considered to be operated in a super-synchronous mode.

[0027] The DFIG 104 is configured to generate an electrical power at the stator winding 130 depending on the operating speed (Nr) of the rotor 136. The electrical power that is generated at the stator winding 130 is hereinafter also referred to as a stator power (P stator). Further, the DFIG 104 is configured to generate or absorb electrical power at the rotor winding 132 depending on the operating speed (Nr) of the rotor 136. For example, the DFIG 104 is configured to generate an electrical power at the rotor winding 132 when the rotor 136 is operated at the super-synchronous speed. The DFIG 104 is configured to absorb the electrical power at the rotor winding 132 when the rotor 136 is operated at the sub-synchronous speed. The electrical power that is generated or absorbed at the rotor winding 132 is hereinafter also referred to as a slip power (Psn_p) or a rotor power (P Rotor). The magnitude of the rotor power (P Rotor) is dependent on a slip value S of the DFIG 104. In one embodiment, the slip value S may be determined using equation (2). Equation (2)

[0028] Moreover, the rotor power (Pnotor) may be determined using equation (3).

P Rotor⁼S * P stator Equation (3)

[0029] The generator-side converter 106 is electrically coupled to the rotor winding 132 of the DFIG 104 via the link 124. The generator-side converter 106 may be an AC -DC converter and configured to convert an AC power into a DC power and vice-versa. The line-side converter 108 may be a DC- AC converter and configured to convert the DC power into an AC power and vice-versa. In some embodiments, each of the generator- side converter 106 and the line-side converter 108 may include one or more switches, for example, semiconductor switches, configured to facilitate power conversion from AC to DC or vice-versa.

[0030] The generator-side converter 106 is electrically coupled to the line-side converter 108 via the DC-link 110. The DC-link 110 includes a plurality of electrical conductors/terminals and at least one DC-bus capacitor 111 electrically coupled between two conductors/terminals of the DC-link 110. Further, the line-side converter 108 may be electrically coupled to the PCC 120 via a circuit breaker 125. The circuit breaker 125 may be a three-phase circuit breaker, a fuse, a contactor, any other electrical protective device, or combinations thereof.

[0031] Furthermore, in some embodiments, the power generation system 100 may also include the auxiliary power source 112 coupled to the DC-link 110. The auxiliary power source 112 is capable of supplying a DC power (Paux) to the DC-link 110. Non-limiting examples of the auxiliary power source 112 may include a photovoltaic (PV) power source, a battery, a fuel cell, a renewable energy based power generator, a non-renewable energy based power generator, or combinations thereof. In certain embodiments, the auxiliary power source 112 may be coupled to the DC-link 110 via a DC-DC converter 140. The DC-DC converter 140 may be operated as a buck converter, a boost converter, or a buck-boost converter.

[0032] Moreover, the energy storage device 114 may include one or more batteries, capacitors, or a combination thereof. The energy storage device 114 may be configured to supply a DC power (PES) to the DC-link 110 or absorb the DC-power (P/ s) from the DC-link 110. In certain embodiments, the energy storage device 114 may be coupled to the DC-link 110 via a DC-DC converter 142. The DC-DC converter 142 may be operated as a buck converter, a boost converter, or a buck-boost converter.

[0033] The power generation system 100 further includes a control sub-system 116 configured to control operation of the power generation system 100. The control sub-system 116 may be operatively coupled to one or more of the prime mover 102, the generator- side converter 106, the line-side converter 108, the circuit breaker 125, the DC-DC converter 140, and the DC-DC converter 142. In some embodiments, the controller sub-system 116 may include one or more sensors such as a sensor 144 and a controller 146.

[0034] In the embodiment of FIG. 1, the sensor 144 is shown as electrically connected to the line-side converter 108. Although, one sensor 144 is shown in FIG. 1, use of more than one sensors is also contemplated within the scope of the present specification. In some other embodiments, the one or more sensors 144 may be electrically coupled to the line-side converter 108, the DC-link 110, the PCC 120, one or more links 122, 124, 126, the circuit breaker 125, or combinations thereof. The sensor 144 may be a current sensor, a voltage sensor, or a combination thereof. The sensor 144 may be configured to generate electrical signals indicative of voltage and/or current at their respective point of connection in the power generation system 100.

[0035] The controller 146 may include a specially programmed general-purpose computer, an electronic processor such as a microprocessor, a digital signal processor, and/or a microcontroller. Further, the controller 146 may 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 controller 146 may be implemented as hardware elements such as circuit boards with processors or as software running on a processor such as a personal computer (PC), or a microcontroller.

[0036] In some embodiments, the controller 146 may be operatively coupled to one or more of the sensor(s) 144, the prime mover 102, the generator- side converter 106, and the line-side converter 108, the circuit breaker 125, the DC-DC converter 140, and the DC-DC converter 142, as depicted in FIG. 1. In the embodiment of FIG. 1, the controller 146 is shown as coupled to one or more of the sensor(s) 144, the prime mover 102, the generator- side converter 106, and the line-side converter 108, the circuit breaker 125, the DC-DC converter 140, and the DC- DC converter 142 via wired control lines (depicted via dashed lines). In some other embodiments, the controller 146 may be operatively coupled to one or more of the sensor(s) 144, the prime mover 102, the generator-side converter 106, and the line-side converter 108, the DC-DC converter 140, and the DC-DC converter 142 over a wireless communication medium. The wireless communication medium may be effected by wireless communication techniques based on Bluetooth^®, Wi-Fi^® (IEEE 802.11), WiMAX^® (IEEE 802.16), Wi-Bro^®, cellular communication techniques, such as, but not limited to global system for mobile (GSM) communications or code division multiple access (CDMA), data communication techniques, including, but not limited to, broadband, 2G, 3G, 4G, or 5G.

[0037] Further, the controller 146 may be configured to detect a failure associated with the line-side converter 108 based on the electrical signals generated by the one or more sensors 144. The controller 146 is further configured to alter, in response to the detection of the failure associated with the line-side converter 108, one or more of the operating speed (Nr) of the rotor 136 of the DFIG 104 and an output power (P Prime mover) of the prime mover 102 based on a power demand (P Demand) at the PCC 120 and a level of electrical power at the DC-link 110 such that an electrical power to meet the power demand (PDemand) at the PCC 120 is supplied via the stator winding 130 to the PCC 120. The electrical power ( PDC-imk ) at the DC-link 110 is hereinafter referred to as a DC-link power (. PDC-IM ). Moreover, the generator- side converter 106 may be configured to control a frequency of a rotor current supplied or absorbed by the generator-side converter 106 to control a frequency of the electrical power at the stator winding 130. Additional details of the control operations performed by the controller 146 are described in conjunction with FIGs. 3 and 4A-4C.

[0038] Advantageously, these operations performed by the controller 146 of the control sub- system 116 in an event of the failure associated with the line-side converter 108, facilitate continued operation of the power generation system 100. Consequently, a supply of the electrical power to the electric grid and/or the electrical loads may not be interrupted leading to improved and reliable power generation system 100.

[0039] FIG. 2 is a block diagram representation of a power generation system 200, in accordance with one embodiment of the present invention. The power generation system 200 of FIG. 2 may be representative of one embodiment of the power generation system 100 of FIG. 1 and includes certain components similar to the components used in FIG. 1. For example, the power generation system 200 includes the DFIG 104, the generator- side converter 106, the line-side converter 108, the DC-link 110, the energy storage device 114, the control sub-system 116, the output power port 118, the PCC 120, the links 122-126, the circuit breaker 125, the transformer 128, and the DC-DC converter 142 connected as shown in FIG. 2. In comparison to FIG. 1, in the embodiment of FIG. 2, a variable speed engine 202 is used as a prime mover and a photovoltaic (PV) power source 204 is used as an auxiliary power source.

[0040] In some embodiments, at a given power level, the variable speed engine 202 may be operated at different speeds. In particular, the variable speed engine 202 may be configured to aid in imparting a rotational motion to the rotor 136 of the DFIG 104. The variable speed engine 202 may be an internal combustion engine or an external combustion engine. Non limiting examples of the internal combustion engine may include a reciprocating engine such as a diesel engine or a petrol engine, or a rotary engine such as a compressor or a gas turbine. Moreover, the variable speed engine 202 may be operated by combustion of various fuels including, but not limited to, diesel, natural gas, petrol, liquefied petroleum gas (LPG), liquefied natural gas (LNG), biogas, producer gas, and the like. The variable speed engine 202 may also be operated using waste heat cycle. It is to be noted that the scope of the present specification is not limited with respect to the types of fuel and the variable speed engine 202 employed in the power generation system 200.

[0041] Moreover, in some embodiments, the PV power source 204 may include one or more PV arrays 206, where each PV array 206 may include at least one PV module 208. A PV module 208 may include a suitable arrangement of a plurality of PV cells (diodes and/or transistors, not shown). The PV power source 204 may generate a DC power depending on solar insolation, weather conditions, and/or time of the day. Accordingly, the PV power source 204 may be configured to supply the DC power (P_aUx) to the DC-link 110.

[0042] In some embodiments, the PV power source 204 may be electrically coupled to the DC-link 110 via the DC-DC converter 210. The DC-DC converter 210 may be electrically coupled between the PV power source 204 and the DC-link 110. The DC power may be supplied from the PV power source 204 to the DC-link 110 via the DC-DC converter 210. The DC-DC converter 210 may be operated as a buck converter, a boost converter, or a buck-boost converter, and may be controlled by the controller 146.

[0043] FIG. 3 is a flow diagram 300 of a method for operating the power generation system of FIG. 1 or FIG. 2, in accordance with one embodiment of the present specification. In the description below, the flow diagram 300 is described with reference to the power generation system 100 of FIG. 1. It may be noted that the method of FIG. 3 may also be applicable to the power generation system 200 of FIG. 2.

[0044] At step 302, the controller 146 is configured to receive an electrical signal from the sensor 144. As noted earlier, the electrical signal received from the sensor 144 is indicative of the voltage and/or the current at a point where the sensor 144 is connected in the power generation system 100. In some embodiments, the electrical signal received from the sensor 144 is indicative of a failure, if any, associated with the line-side converter 108.

[0045] At step 304, the controller 146 may be configured to detect the failure associated with the line-side converter 108. The controller 146 may detect the failure associated with the line-side converter 108 based on the electrical signal received from the sensor 144. By way of example, the controller 146 may detect the failure associated with the line-side converter 108 based on one or more properties such as a magnitude, a frequency, or a phase of the electrical signal. Additional details of the detection of the failure are described with reference to FIG. 4A. At step 304, if no failure associated with the line-side converter 108 is detected, the control may be passed to step 302. However, at step 304, if a failure associated with the line-side converter 108 is detected, the controller 146 may perform step 306.

[0046] At step 306, the controller 146 may alter the operating speed (Nr) of the rotor 136 of the DFIG 104 and/or the output power (P Prime mover) of the prime mover 102 (alternatively, an output power (P Engine) of the variable speed engine 202 in case of FIG. 2) based on the power demand (P Demand) at the PCC 120 and the level of the DC-link power (PDC-imk). In some embodiments, the operating speed (Nr) and the output power (Pprime mover) may be altered such that an electrical power to meet the power demand (PDemand) at the PCC 120 is supplied via the stator winding 130 of the DFIG 104 to the PCC 120. Details of altering the operating speed (Nr) of the rotor 136 are described with reference to FIGs 4B-4C.

[0047] Moreover, in certain embodiments, at step 308, the controller 146 may be configured to control at least one of a magnitude of the stator voltage and a frequency of the stator power via the generator- side converter 106. In particular, the controller 146 is configured to control at least one of a frequency of a rotor current supplied from or absorbed by the generator-side converter 106 to the rotor winding 132 and a magnitude of a rotor voltage to control the frequency of the stator power or the magnitude of the stator voltage, respectively. The term “rotor current” refers to a current being supplied from or absorbed by the rotor winding 132. Similarly, term“rotor voltage” refers to a voltage between two phases of the rotor winding 132.

[0048] FIGs. 4A, 4B, and 4C represent a flow diagram 400 of a detailed method for operating the power generation system 100 of FIG. 1 or FIG. 2, in accordance with one embodiment of the present specification. In the description below, the flow diagram 400 is described with reference to the power generation system 100 of FIG. 1. It may be noted that the method 400 of FIG. 4 may also be applicable to the power generation system 200 of FIG. 2

[0049] At step 402, the controller 146 is configured to receive the electrical signal from the sensor 144, as previously described with reference to step 302 of FIG. 3. Further, at step 404, the controller 146 may be configured to perform a check to determine whether at least one of the line-side converter 108 or the circuit breaker 125 has malfunctioned. The controller 146 may determine the malfunctioning of one or both of the line-side converter 108 and the circuit breaker 125 based on the electrical signal received at step 402. The malfunctioning associated with the line-side converter 108 may include failure of all three phase-legs of the line-side converter 108. The failure of the phase-legs of the line-side converter 108 may be caused due to failures such as short-circuit, overheating, any physical damage, and/or burning, of one or more of switches contained in the phase-legs. Similarly, the failure of the circuit breaker 125 may be caused due to failures such as short-circuit, overheating, any physical damage, and/or burning, of the circuit breaker 125.

[0050] At step 404, if it is determined that at least one of the circuit breaker 125 or all phase- legs of the line-side converter 108 have malfunctioned, the controller 146 may proceed to perform step 410 (described later). However, at step 404, if it is determined that at least one of the circuit breaker 125 or all phase-legs of the line-side converter 108 have not malfunctioned, the controller 146 may perform another check at step 406. At step 406, the controller 146 may determine whether only one phase-leg of the line-side converter 108 has malfunctioned based on the electrical signal received at step 402. At step 406, if it is determined that only one phase-leg of the line-side converter 108 has malfunctioned, the controller 146 may proceed to perform step 412 (described later in conjunction with FIG. 4C). However, at step 406, if it is determined that only one phase-leg of the line-side converter 108 has not malfunctioned, the controller 146 may perform another check at step 408. At step 408, the controller 146 may determine, based on the electrical signal received at step 402, whether only two phase-legs of the line-side converter 108 have malfunctioned. At step 408, if it is determined that only two phase-legs of the line-side converter 108 have malfunctioned, the controller 146 may proceed to perform step 414 (described later in conjunction with FIG. 4C). However, at step 408, if it is determined that only two phase-legs of the line-side converter 108 have not malfunctioned, the controller 146 may determine that there exists no failure associated with the line-side converter 108 and performs step 402 again.

[0051] Referring now to step 410 (see FIG. 4B), the controller 146 may perform a check to determine whether a state of charge (SOC) of the energy storage device 114 is greater than a threshold SOC value ( SOCm ). The SOC of the energy storage device 114 may be determined by the controller 146 based on a voltage level at an input of the DC-DC converter 142, a current supplied from the energy storage device 114 to the DC-link 110, or a combination thereof. Further, the threshold SOC value (SOCm) may be representative of a minimum value of the SOC which needs to be maintained at the energy storage device 114. In some embodiments, the threshold SOC value (SOCm) may be stored in a memory device (not shown) associated with the controller 146. The controller 146 may access the threshold SOC value (SOCm) from the memory device. In certain embodiments, the threshold SOC value (SOCm) may be customizable by an operator of the power generation system 100.

[0052] At step 410, if it is determined that the SOC of the energy storage device 114 is greater than the threshold SOC value (SOCm), the controller 146, at step 416, may be configured to operate the DFIG 104 in the sub-synchronous mode. When operated in the sub- synchronous mode, the electrical power from the DC-link 110 is supplied to the PCC 120 via the stator winding 130. The operation of the DFIG 104 in the sub-synchronous mode includes operating the DFIG 104 at a sub-synchronous speed, as described below. In some embodiments, a method for operating the DFIG 104 in the sub-synchronous mode at step 416 includes sub-steps 418, 420, and 422.

[0053] At step 418, the controller 146 may be configured to determine a sub-synchronous speed (Nsubi) of the rotor 136 based on the level of the DC-link power (PDC-imk) and the power demand (P Demand) at the PCC 120. In a non-limiting example, the controller 146 may determine the sub-synchronous speed {Nsubi) using following equation (4).

Equation (4)

where, P Demand ^~ Pstator -

[0054] Moreover, at step 418, the DC-link power ( PDC-IM ) may be calculated using following equation (5).

PDC-Unk = PRotor = Paux + \ ^PES \ Equation (5) where, Paux represents electrical power generated by the auxiliary power source 112 and IP s represents electrical power supplied from the energy storage device 114.

[0055] Further, at step 420, the controller 146 may be configured to determine a desired output power ( P Prime mover_Desired_l ) of the prime mover 102 based on the level of the DC-link power {PDC-hnk) and the power demand (PDemand) at the PCC 120. In a non-limiting example, the controller 146 may determine the desired output power (P Prime mover Desired j) of the prime mover 102 using following equation (6).

Pprime mover _Desired_ 1 ^— PDemand ^~ I P DC -link I Equation (6)

[0056] Moreover, at step 422, the controller 146 may be configured to modify the operating speed Nr) of the rotor 136 such that the rotor 136 is rotated at the determined sub-synchronous speed {Nsubi). The controller 146 may increase or decrease the operating speed (Mr) of the rotor 136 such that the operating speed {Nr) matches the sub-synchronous speed {Nsubi). In order to modify the operating speed {Nr) of the rotor 136, the controller 146 may send a speed command to the prime mover 102 to operate at a speed such that the rotor 136 is rotated at the determined sub-synchronous speed {Nsubi). Further, the controller 146 is configured to modify the output power {Pprime mover) of the prime mover 102 such that the prime mover 102 generates the desired output power {Pprime mover = Pprime mover Desiredj) as determined using the equation (6). In order to modify the output power of the prime mover 102, the controller 146 may send a power command to the prime mover 102 such that the prime mover 102 generates the desired output power (Pprime mover Desired J) as determined using the equation (6).

[0057] Referring again to step 410, if it is determined that the SOC of the energy storage device 114 is not greater than (i.e., lower than or equal to) the threshold SOC value {SOCTH), the controller 146 may perform another check at step 424. At step 424, a check is performed to determine whether the output power {Paux) of the auxiliary power source 112 is greater than an auxiliary power threshold value {POUXTH). The output power {Paux) of the auxiliary power source 112 may be determined by the controller 146 based on a voltage at an output of the DC- DC converter 140, a current supplied from the DC-DC converter 140 to the DC-link 110, or a combination thereof. Further, the auxiliary power threshold value {Pauxm) may be representative of a value of the output power {Paux) below which the output power {Paux) is not sufficient to charge the energy storage device 114. By way of a non-limiting example, the auxiliary power threshold value {Pauxm) may be equal to zero. In some embodiments, the auxiliary power threshold value {Pauxm) may be stored in the memory device associated with the controller 146. The controller 146 may access the auxiliary power threshold value {Pauxm) from the memory device. In certain embodiments, the auxiliary power threshold value {Pauxm) may be customizable by an operator of the power generation system 100.

[0058] At step 424, if it is determined that the output power {Paux) of the auxiliary power source 112 is not greater than the auxiliary power threshold value {Pauxm), the controller 146, at step 426, may be configured to operate the DFIG 104 in the super-synchronous mode. The operation of the DFIG 104 in the super-synchronous mode includes operating the DFIG 104 at a super-synchronous speed, as described below. In some embodiments, a method for operating the DFIG 104 in the super-synchronous mode at step 426 includes sub-steps 428, 430, and 432.

[0059] At step 428, the controller 146 may be configured to determine a super-synchronous speed {Nsu_P) of the rotor 136 based on the level of the DC-link power {PDC-IM) and the power demand {PDemand) at the PCC 120. In a non-limiting example, the controller 146 may determine the super-synchronous speed {Nsup) using following equation (7).

Equation (7)

Where, P_Demand = Pstator and P_DC-imk = ^PES charge - PES Charge represents a power required to charge the energy storage device 114.

[0060] Further, at step 430, the controller 146 may be configured to determine a desired output power {P Prime mover_Desired_2 ) of the prime mover 102 based on the level of the DC-link power {PDC-iink) and the power demand {PDemand) at the PCC 120. In a non-limiting example, the controller 146 may determine the desired output power {P Prime mover Desired j) of the prime mover 102 using following equation (8).

Equation (8)

[0061] Moreover, at step 432, the controller 146 may be configured to modify the operating speed {Nr) of the rotor 136 such that the rotor 136 is rotated at the determined super- synchronous speed {Nsup). The controller 146 may increase or decrease the operating speed {Nr) of the rotor 136 such that the operating speed {Nr) matches the super-synchronous speed {Nsup). In order to modify the operating speed {Nr) of the rotor 136, the controller 146 may send a speed command to the prime mover 102 to operate at a speed such that the rotor 136 is rotated at the determined super-synchronous speed {Nsu_P). Further, the controller 146 is configured to modify the output power (P Prime mover) of the prime mover 102 such that the prime mover 102 generates the desired output power (P Prime mover = P Prime mover Desired ) as determined using the equation (8). In order to modify the output power of the prime mover 102, the controller 146 may send a power command to the prime mover 102 such that the prime mover 102 generates the desired output power (P prime mover Desired ) as determined using the equation (8)·

[0062] The DFIG 104, when operated at the super-synchronous speed (Nsu_P), generates the rotor power (Pp₀tor) at the rotor winding 132. Accordingly, at step 434, the controller 146 may be configured to charge the energy storage device 114 by supplying the rotor power (P Rotor) from the rotor winding 132 to the energy storage device 114 via the generator-side converter

106.

[0063] Moving to step 424 again, if it is determined that the output power (Paux) of the auxiliary power source 112 is greater than the auxiliary power threshold value ( POUXTH ), the controller 146 may determine that the output power (Paux) is sufficient to charge the energy storage device 114 while still supplying some power to the PCC 120 via the generator-side converter 106 and the stator winding 130. Therefore, if it is determined that the output power (Paux) of the auxiliary power source 112 is greater than the auxiliary power threshold value (POUXTH), the controller 146, at step 436, may charge the energy storage device 114 by supplying a portion (Pauxj) of Paux to the energy storage device 114. To charge the energy storage device 114, the controller 146 operates the DC-DC converter 142 such that the portion (Pauxj) from the DC-link 110 is supplied to the energy storage device 114 via the DC-DC converter 142.

[0064] Moreover, at step 438, the controller 146 may be configured to operate the DFIG 104 in the sub-synchronous mode. In some embodiments, a method for operating the DFIG 104 in the sub-synchronous mode, includes sub-steps 440, 442, and 444. At step 440, the controller 146 may be configured to determine a sub-synchronous speed (Nsubi) of the rotor 136 based on a remaining portion (Pauxj) of Paux and the power demand (P Demand) at the PCC 120. In a non-limiting example, the controller 146 may determine the remaining portion (Pauxj) using equation (9) and the sub-synchronous speed (Nsubi) using following equation (10).

1 P aux_ 2— ¹ P aux— ¹ P aux 1 Equation (9)

r aux

N S, ub 2 = N_S * ( 1 - 1 I) Equation (10)

P Demand

Where, P Demand ^~ ^Stator ¾fld Paux 2 P Rotor

[0065] Further, at step 442, the controller 146 may be configured to determine a desired output power (P prime mover Desired j) of the prime mover 102 based on the remaining portion (Pauxj) and the power demand {l* Demand) at the PCC 120. In a non-limiting example, the controller 146 may determine the desired output power (P Prime mover Desired j) of the prime mover 102 using following equation (11).

Equation (11)

[0066] Moreover, at step 444, the controller 146 may be configured to modify the operating speed (Nr) of the rotor 136 such that the rotor 136 is rotated at the determined sub-synchronous speed (Nsubi). The controller 146 may increase or decrease the operating speed (Nr) of the rotor 136 such that the operating speed (Nr) matches the sub-synchronous speed (Nsubi). In order to modify the operating speed (Nr) of the rotor 136, the controller 146 may send a speed command to the prime mover 102 to operate at a speed such that the rotor 136 is rotated at the determined sub-synchronous speed (Nsubi). Further, the controller 146 is configured to modify the output power (P prime mover) of the prime mover 102 such that the prime mover 102 generates the desired output power (Pprime mover P Prime mover_Desired_3 ) lS determined using the equation (11). In order to modify the output power of the prime mover 102, the controller 146 may send a power command to the prime mover 102 such that the prime mover 102 generates the desired output power (Pprime mover Desired j) as determined using the equation (11).

[0067] Referring to step 406 of FIG. 4A, if it is determined that only one phase-leg of the line-side converter 108 has malfunctioned and that two of three phase-legs of the line-side converter 108 are still normally functioning, the process moves to step 412 of FIG. 4C. Accordingly, at step 412, the controller 146 may discontinue operating the one malfunctioned phase-leg of the line-side converter 108 by sending one or more control commands to the line- side converter 108. Moreover, at step 446, the controller 146 may be configured to minimize electrical power unbalance between one or more phase lines at the PCC 120 via remaining one or more phase-legs other than the malfunctioned phase-leg (i.e., normally operating phase-legs) of the line-side converter 108. The electrical power unbalance may be caused due to variations in power demand at different phase lines at the PCC 120. To minimize this electrical power unbalance, the controller 146 may aid in operating the healthy / normally functioning phase- legs to supply electrical power to or absorb the electrical power from the respective phase line at the PCC 120. Subsequent to step 446, the controller 146 may move control to step 410 of FIG. 4B.

[0068] Further, referring to step 408 of FIG. 4A, if it is determined that only two phase-legs of the line-side converter 108 have malfunctioned and that one phase-legs of the line-side converter 108 is still normally functioning, the process moves to step 414 of FIG. 4C. Accordingly, at step 414, the controller 146 may discontinue operating the two-malfunctioned phase-legs of the line-side converter 108 by sending one or more control commands to the line- side converter 108. Moreover, at step 448, the controller 146 may be configured to minimize electrical power unbalance between one or more phase lines at the PCC 120 via the remaining one phase-legs other than the two-malfunctioned phase-legs (i.e., normally operating phase- leg) of the line-side converter 108. To minimize this electrical power unbalance, the controller 146 may aid in operating the healthy / normally functioning phase-leg to supply electrical power to or absorb the electrical power from the respective phase line at the PCC 120. Subsequent to step 448, the controller 146 may move control to step 410 of FIG. 4B.

[0069] FIGs. 5A, 5B, and 5C respectively depict graphical representations 500, 502, and 504 showing various power levels and operating speed of the rotor 136 of the DFIG 104 in the power generation systems 100, 200 of FIGs. 1-2, in accordance with one embodiment of the present specification. By way of example, the graphical representations 500, 502, and 504 are presented for a configuration of the power generation system 100 (or 200) where the DFIG 104 includes the rotor 136 having two poles (p= 2), Ns=3000 rpm, a frequency of the stator power (. P stator ) being 50 hertz (Hz), and the prime mover 102 (or the variable speed engine 202) of 18 kW rated power. In particular, the graphical representations 500, 502, and 504 corresponds to different values of the power demand {P Demand), for example, 10 kW, 15 kW, and 5 kW, respectively, at the PCC 120.

[0070] In each of the graphical representations 500-504, the X-axis and Y-axis are respectively represented by reference numerals 506 and 508. Further, in each of the graphical representations 500-504, a curve identified by reference numeral 510 represents a boundary curve for the stator power (. P stator ) with respect to different values of the operating speed (Mr) of the rotor 136. The boundary curve for the stator power ( Pstator ) is hereinafter referred to as a stator power boundary 510. In particular, the stator power boundary 510 may represent maximum values of the stator power ( Pstator ) with respect to different values of the operating speed (Nr) of the rotor 136 for the configuration of the power generation system 100 noted hereinabove.

[0071] Similarly, in each of the graphical representations 500-504, a curve identified by reference numeral 512 represents a boundary curve for the rotor power ( Pnotor ) with respect to different values of the operating speed (Nr) of the rotor 136 for the configuration of the power generation system 100 noted hereinabove. The boundary curve for the rotor power (Pnotor) is hereinafter referred to as a rotor power boundary 512. A portion of the rotor power boundary 512 with negative values represent limit of the rotor power (P Rotor) when the DFIG 104 is operated in the sub-synchronous mode (see steps 416, 438 of FIG. 4B). In particular, absolute values of the rotor power boundary 512, when the rotor power boundary 512 has a negative sign, represent a limit of the rotor power (. PRotor ) that can be absorbed by the rotor winding 132 from the generator- side converter 106 at the corresponding operating speed {Nr) and the stator power {P Stator).

[0072] A portion of the rotor power boundary 512 with positive values represent limit of the rotor power ( PRotor ) when the DFIG 104 is operated in the super-synchronous mode (see steps 426 of FIG. 4B). In particular, values of the rotor power boundary 512 when the rotor power boundary 512 has a positive sign, represents a limit of the rotor power (P Rotor) that can be supplied from the rotor winding 132 to the generator- side converter 106 at the corresponding operating speed (Nr) and the stator power (P stator).

[0073] Moreover, in each of the graphical representations 500-504, a curve identified by reference numeral 514 represents a boundary curve for the output power {P Prime mover) of the prime mover 102 to ensure the stator power (P stator) and the rotor power (P Rotor) within the stator power boundary 510 and the rotor power boundary 512, respectively.

[0074] Referring now to the graphical representation 500 of FIG. 5 A, a curve 516 represents a power demand (PDemand) of 10 kW at the PCC 120. Therefore, if the failure associated with the line-side converter 108 is detected by the controller 146, the DFIG 104 may be operated such that the stator power (P stator) of 10 kW produced to meet the power demand (PDemand). Further, a curve 518 represents values of the rotor power (PRotor) corresponding to the stator power (P stator) of 10 kW with respect to different values of the operating speed (Nr) of the rotor 136. By way of example, the rotor power (PRotor) may be derived using the equation (3).

[0075] During operation, the rotor power (PRotor) may be equivalent to the DC-link power ( P DC-imk ) which may be any value on the curve 518. By way of example, at step 418, PRotor = P DC-iink = Paux+ PES. By way of another example, at step 426, PRotor = PDC-imk = PES charge. By way of yet another example, at step 438, PRotor = PDC-imk = Paux .

[0076] Furthermore, a curve 520 represents values of the desired output power of the prime mover 102 corresponding to the stator power (P stator) of 10 kW with respect to different values of the operating speed (Nr) of the rotor 136. The desired output power may be determined as described in conjunction with step 420, 430, or 442. Moreover, as indicated in the graphical representation 500, the DFIG 104 may not be operated below about 1060 rpm as at the speeds below about 1060 rpm, the rotor power (PRotor) decreases below the rotor power boundary 512.

[0077] Moving to the graphical representation 502 of FIG. 5B, a curve 522 represents a power demand (PDemand) of 15 kW at the PCC 120. Further, a curve 524 represents values of the rotor power (PRotor) corresponding to the stator power (P stator) of 15 kW with respect to different values of the operating speed (Nr) of the rotor 136. Furthermore, a curve 526 represents values of the desired output power of the prime mover 102 corresponding to the stator power (P stator) of 15 kW with respect to different values of the operating speed (Nr) of the rotor 136. As indicated in the graphical representation 502, the DFIG 104 may not be operated below about 1400 rpm as at the speeds below about 1400 rpm, the rotor power (P Rotor) decreases below the rotor power boundary 512.

[0078] Transitioning to the graphical representation 504 of FIG. 5C, a curve 528 represents a power demand (PDemand) of 5 kW at the PCC 120. Further, a curve 530 represents values of the rotor power (PRotor) corresponding to the stator power (P stator) of 5 kW with respect to different values of the operating speed (Nr) of the rotor 136. Furthermore, a curve 532 represents values of the desired output power of the prime mover 102 corresponding to the stator power (P stator) of 5 kW with respect to different values of the operating speed (Nr) of the rotor 136.

[0079] In accordance with some aspects of the present specification, configurations of the power generation systems 100, 200 exhibit certain advantages over the traditional hybrid power generation systems. When, any fault associated with the line-side converter 108 is detected, the controller 146 facilitates continued operation of the power generation system 100 via the generator- side controller 106. Consequently, a supply of the electrical power to the electric grid and/or the electrical loads may not be interrupted leading to improved and reliable power generation system 100, 200. Further, due to such continued operation of the power generation system 100, 200, use of the electrical power generated by the auxiliary power source 112 or the PV power source 204 is increased in comparison to the traditional hybrid power generation systems. Moreover, due the enhanced utilization of the electrical power generated by the auxiliary power source 112 or the PV power source 204, a cost per unit of the electricity produced by the power generation system 100, 200 is also reduced in comparison to the cost per unit of the electricity produced by the traditional hybrid power generation systems.

[0080] Any of the foregoing steps and/or system elements may be suitably replaced, reordered, or removed, and additional steps and/or system elements may be inserted, depending on the needs of a particular application.

[0081] This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. Aspects from the various embodiments described, as well as other known equivalents for each such aspects, can be mixed and matched by one of ordinary skill in the art to construct additional embodiments and techniques in accordance with principles of this application.

Claims

WE CLAIM

1. A method for controlling operation of a power generation system (100, 200) comprising a prime mover (102, 202), a doubly-fed induction generator (DFIG) (104), a generator-side converter (106), a line-side converter (108) coupled to the generator-side converter (106) via a direct current (DC)-link 110, an energy storage device (114) coupled to the DC-link (110) to supply an electrical power to the DC-link (110), and a point of common coupling (PCC) (120) at which stator winding (130) from a stator (134) of the DFIG (104) are coupled to the line-side converter (108), the method comprising:

detecting a failure associated with the line-side converter (108); and

altering, in response to the detected failure, one or more of an operating speed of a rotor (136) of the DFIG (104) and an output power of the prime mover (102, 202) based on a power demand at the PCC (120) and a level of the electrical power at the DC-link (110) such that an electrical power to meet the power demand at the PCC (120) is supplied via a stator winding (130) of the DFIG (104) to the PCC (120).

2. The method as claimed in claim 1, further comprising determining if a state of charge (SOC) of the energy storage device (114) is higher than a threshold SOC value.

3. The method as claimed in claim 2, wherein altering the one or more of the operating speed of the rotor (136) and the output power of the prime mover (102, 202) comprises operating, in response to determining that the SOC of the energy storage device (114) is higher than the threshold SOC value, the DFIG (104) in a sub-synchronous mode such that the electrical power from the DC-link (110) is supplied to the PCC (120) via the stator winding (130).

4. The method as claimed in claim 3, wherein operating the DFIG (104) in the sub- synchronous mode comprises:

determining a sub -synchronous speed of the rotor (136) based on the level of the electrical power at the DC-link (110) and the power demand at the PCC (120);

modifying the operating speed of the rotor (136) such that the rotor (136) is rotated at the determined sub-synchronous speed;

determining a desired output power of the prime mover (102, 202) based on the level of the electrical power at the DC-link (110) and the power demand at the PCC (120); and modifying the output power of the prime mover (102, 202) such that the prime mover (102, 202) generates the desired output power.

5. The method as claimed in claim 2, wherein the power generation system (100, 200) further comprises an auxiliary power source (112, 204) coupled to the DC-link (110), and further comprising determining if an output power of the auxiliary power source (112, 204) is not greater than an auxiliary power threshold value if it is determined that the SOC of the energy storage device (114) is not higher than the threshold SOC value.

6. The method as claimed in claim 5, wherein altering the one or more of the operating speed of the rotor (136) and the output power of the prime mover (102, 202) comprises operating, in response to determining that the output power of the auxiliary power source (112, 204) is not greater than the auxiliary power threshold value, the DFIG (104) in a super-synchronous mode.

7. The method as claimed in claim 6, wherein operating the DFIG (104) in the super-synchronous mode comprises:

determining a super-synchronous speed of the rotor (136) based on the level of the electrical power at the DC-link (110) and the power demand at the PCC (120);

modifying the operating speed of the rotor (136) such that the rotor (136) is rotated at the determined super-synchronous speed;

8. The method as claimed in claim 6, further comprising charging the energy storage device (114) by supplying an electrical power from the rotor winding (132) via the generator-side converter (106).

9. The method as claimed in claim 5, further comprising, in response to determining that the output power of the auxiliary power source (112, 204) is greater than the auxiliary power threshold value, charging the energy storage device (114) by supplying a portion of the output power of the auxiliary power source (112, 204) to the energy storage device (114).

10. The method as claimed in claim 9, wherein altering the one or more of the operating speed of the rotor (136) and the output power of the prime mover (102, 202) comprises operating the DFIG (104) in a sub-synchronous mode such that a remaining portion of the output power of the auxiliary power source (112, 204) is supplied to the PCC (120) via the stator winding (130).

11. The method as claimed in claim 10, wherein operating the DFIG (104) in the sub-synchronous mode comprises: determining a sub-synchronous speed of the rotor (136) based on the remaining portion of the output power of the auxiliary power source (112, 204) and the power demand at the PCC (120);

determining a desired output power of the prime mover (102, 202) based on the remaining portion of the output power of the auxiliary power source (112, 204) and the power demand at the PCC (120); and

modifying the output power of the prime mover (102, 202) such that the prime mover (102, 202) generates the desired output power.

12. The method as claimed in claim 1, further comprising controlling at least one of a magnitude of a stator voltage and a frequency of the electrical power at the stator winding (130) via the generator- side converter (106).

13. The method as claimed in claim 1 , wherein detecting the failure associated with the line-side converter (108) comprises determining that at least one of the line-side converter (108) or a circuit breaker (125) has malfunctioned, wherein the circuit breaker (125) is coupled between the line-side converter (108) and the PCC (120).

14. The method as claimed in claim 1, wherein detecting the failure associated with the line-side converter (108) comprises determining that one or more phase-legs of the line- side converter (108) has malfunctioned.

15. The method as claimed in claim 14, further comprising minimizing, if one or more phase-legs of the line-side converter (108) has malfunctioned, electrical power unbalance between one or more phase lines at the PCC (120) via one or more phase-legs other than the malfunctioned phase legs.

16. A control sub-system (116) for controlling an operation of a power generation system (100, 200) comprising a prime mover (102, 202), a doubly-fed induction generator (DFIG) (104), a generator-side converter (106), a line-side converter (108) coupled to the generator- side converter (106) via a direct current (DC)-link 110, an auxiliary power source (112, 204) and/or an energy storage device (114) coupled to the DC-link (110) to supply an electrical power to the DC-link (110), and a point of common coupling (PCC) (120) at which stator winding (130) from a stator (134) of the DFIG (104) are coupled to the line-side converter (108), the control sub-system (116) comprising: one or more sensors (144) coupled to the line-side converter (108) and configured to generate electrical signals; and

a controller (146) operatively coupled to the prime mover (102, 202), the line-side converter (108), the generator- side converter (106), and the one or more sensors (144), wherein the controller (146) is configured to:

detect the failure associated with the line-side converter (108) based on the electrical signals generated by the one or more sensors (144); and

alter, in response to the detection of the failure associated with the line-side converter (108), one or more of an operating speed of a rotor (136) of the DFIG (104) and an output power of the prime mover (102, 202) based on a power demand at the PCC (120) and a level of electrical power at the DC-link (110) such that an electrical power to meet the power demand at the PCC (120) is supplied via the stator winding (130) to the PCC (120).

17. The control sub-system (116) as claimed in claim 16, wherein the prime mover (102, 202) comprises a variable speed engine (202), and wherein the auxiliary power source (112, 204) comprises a photovoltaic power source (204).

18. The control sub-system (116) as claimed in claim 16, wherein the controller (146) is further configured to determine if a state of charge (SOC) of the energy storage device (114) is higher than a threshold SOC value.

19. The control sub-system (116) as claimed in claim 18, wherein the controller (146) is further configured to operate the DFIG (104) in a sub-synchronous mode such that the electrical power from the DC-link (110) is supplied to the PCC (120) via the stator winding (130) if it is determined that the SOC of the energy storage device (114) is higher than the threshold SOC value.

20. The control sub-system (116) as claimed in claim 18, wherein the controller (146) is further configured to:

operate the DFIG (104) in a super-synchronous mode if it is determined that the output power of the auxiliary power source (112, 204) is lower than an auxiliary power threshold value and the SOC of the energy storage device (114) is not higher than the threshold SOC value; and

charge the energy storage device (114) by supplying a portion of the output power of the auxiliary power source (112, 204) to the energy storage device (114).

21. The control sub-system (116) as claimed in claim 16, wherein to detect the failure associated with the line-side converter (108) the controller (146) is configured to determine:

that the line-side converter (108) as malfunctioned;

that a circuit breaker (125) has malfunctioned, wherein the circuit breaker (125) is coupled between the line-side converter (108) and the PCC (120);

that one phase-leg of the line-side converter (108) has malfunctioned; or

that two phase-legs of the line-side converter (108) have malfunctioned.

22. A power generation system (100, 200), comprising:

a variable speed engine (202);

a doubly-fed induction generator (DFIG) (104) mechanically coupled to the variable speed engine (202), wherein the DFIG (104) comprises a stator winding (130) disposed on a stator (134) and a rotor winding (132) disposed on a rotor (136), wherein the stator winding (130) is electrically coupled to a point of common coupling (PCC) (120);

a generator-side converter (106) electrically coupled to the rotor winding (132);

a line-side converter (108) electrically coupled to the PCC (120), wherein the line-side converter (108) is electrically coupled to the generator- side converter (106) via a direct current (DC) link;

an auxiliary power source (112, 204) and an energy storage device (114) coupled to the DC-link (110) to supply an electrical power to the DC-link (110); and

a control sub-system (116) operatively coupled to the variable speed engine (202), the line-side converter (108), and the generator- side converter (106), the control sub-system (116) comprising:

one or more sensors (144);

a controller (146) operatively coupled to the variable speed engine (202), the line-side converter (108), the generator- side converter (106), and the one or more sensors (144), wherein the controller (146) is configured to:

detect the failure associated with the line-side converter (108); and in response to the detection of the failure, alter one or more of an operating speed of a rotor (136) of the DFIG (104) and an output power of the variable speed engine (202) based on a power demand at the PCC (120) and a level of electrical power at the DC-link (110) such that an electrical power to meet the power demand at the PCC (120) is supplied via the stator winding (130) to the PCC (120).