WO2019103837A1

WO2019103837A1 - A power generation system and a method for operating the same

Info

Publication number: WO2019103837A1
Application number: PCT/US2018/059343
Authority: WO
Inventors: Arvind Kumar Tiwari; Yashomani Y. Kolhatkar
Original assignee: General Electric Company
Priority date: 2017-11-22
Filing date: 2018-11-06
Publication date: 2019-05-31

Abstract

A power generation system (100, 300) is presented. The power generation system (100, 300) includes a reference direct current (DC) bus (104) and a plurality of doubly-fed induction generator (DFIG) based power generation sub-systems (102-1, 102-2) electrically coupled in parallel with each other via the reference DC-bus (104). Each of the plurality of DFIG based power generation sub-systems (102-1, 102-2) includes a DFIG (204), a rotor-side converter (206) and a line-side converter (208) coupled to the DFIG (204). The line-side converter (208) and the rotor-side converter (206) are electrically coupled to each other via a local DC-bus (116-1, 116-2). The local DC-bus (116-1, 116-2) of each of the plurality of DFIG based power generation sub-systems (102-1, 102-2) is coupled to the reference DC-bus (104). Moreover, the power generation system (100, 300) includes an auxiliary power source (108) and an energy storage device (110) electrically coupled to the reference DC-bus (104).

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 power generation system having a plurality of doubly-fed induction generator (DFIG) based power generation sub-systems coupled in parallel with each other.

[0002] Some currently available 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 power generation system, the auxiliary power source is coupled to the DFIG via one or more power converter(s). 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] Typically, such power generation systems are designed for a fixed rated capacity. Therefore, if a power demand from such power generation system increases, the power generation systems may have to be operated very close to the respective fixed rated capacity leading to reliability issues. Alternatively, internal components of the traditional generation systems are required to be replaced to address the increased power demand.

BRIEF DESCRIPTION

[0004] In accordance with one embodiment of the present specification, a power generation system is presented. The power generation system includes a reference direct current (DC) bus. The power generation system further includes plurality of doubly-fed induction generator (DFIG) based power generation sub-systems coupled in parallel with each other via the reference DC-bus, where each of the plurality of DFIG based power generation sub-systems includes a DFIG, a rotor-side converter and a line-side converter coupled to the DFIG, where the line-side converter and the rotor-side converter are electrically coupled to each other via a local DC-bus, and where the local DC-bus of each of the plurality of DFIG based power generation sub-systems is coupled to the reference DC-bus. Moreover, the power generation system includes an auxiliary power source and an energy storage device coupled to the reference DC-bus.

[0005] 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 plurality of DFIG based power generation sub-systems coupled in parallel to each other via a reference DC-bus and an alternating current (AC) distribution bus. The method includes determining whether there is a mismatch between an AC power requirement of the AC distribution bus and a local AC power generated by the plurality of DFIG based power generation sub-systems. The method further includes communicating, in response to determining the mismatch, synchronization command to a local controller of corresponding one or more of the plurality of DFIG based power generation sub-systems to enable synchronization of the local AC power of the one or more of the plurality of DFIG based power generation sub-systems with the AC power requirement of the AC distribution bus, where each of the plurality of DFIG based power generation sub-systems includes a DFIG, a rotor-side converter and a line-side converter coupled to the DFIG, where the line-side converter and the rotor-side converter are electrically coupled to each other via a local DC-bus, where the local DC-bus of each of the plurality of DFIG based power generation sub-systems is coupled to the reference DC-bus, and wherein the local controller is operatively coupled to the line-side converter and the rotor-side converter.

DRAWINGS

[0006] 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:

[0007] FIG. l is a block diagram representation of a power generation system, in accordance with one embodiment of the present specification;

[0008] FIG. 2 is a block diagram representation of a doubly-fed induction generator (DFIG) based power generation sub-system employed in the power generation system of FIG. 1, in accordance with one embodiment of the present specification;

[0009] FIG. 3 is a block diagram representation of a power generation system, in accordance with one embodiment of the present specification;

[0010] FIG. 4 is a flow diagram of a method for forming a power generation system, in accordance with one embodiment of the present specification; and

[0011] FIG. 5 is a flow diagram of a method for operating a power generation system, in accordance with one embodiment of the present specification.

DETAILED DESCRIPTION

[0012] 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.

[0013] 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.

[0014] 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.

[0015] In accordance with some embodiments of the present specification, a power generation system is presented. The power generation system includes a reference direct current (DC)-bus. The power generation system further includes a plurality of doubly-fed induction generator (DFIG) based power generation sub-systems coupled in parallel with each other via the reference DC-bus, where each of the plurality of DFIG based power generation sub-systems includes a DFIG, a line-side converter and a rotor-side converter coupled to the DFIG, where the line-side converter and the rotor- side converter are electrically coupled to each other via a local DC-bus, and where the local DC-bus of each of the plurality of DFIG based power generation sub-systems is coupled to the reference DC- bus. Moreover, the power generation system includes an auxiliary power source and an energy storage device coupled to the reference DC-bus.

[0016] FIG. 1 is a block diagram representation of a power generation system 100, in accordance with one embodiment of the present specification. In some embodiments, the power generation system 100 may include one or more of a plurality of DFIG based power generation sub-systems 102-1, 102- 2, a reference DC-bus 104, an alternating current (AC) distribution bus 106, an auxiliary power source 108, and an energy storage device 110. Moreover, the power generation system 100 may also include a supervisory controller 112 coupled to the plurality of the DFIG based power generation sub-systems 102-1, 102-2.

[0017] The plurality of DFIG based power generation sub-systems 102-1, 102-2 is coupled to the reference DC-bus 104. In some embodiments, the DFIG based power generation sub-systems 102-1, 102-2 are connected in parallel with each other via the reference DC-bus 104 and/or the AC distribution bus 106. For ease of illustration and representation in FIG. 1, only few elements, such as a local DC- bus 116-1, 116-2, a local AC -bus 118-1, 118-2, and a local controller 120-1, 120-2, of the DFIG based power generation sub-system 102-1, 102-2 are shown. Detailed block diagram and description of one such DFIG based power generation sub-system 102-1 is provided in conjunction with FIG. 2. Moreover, details of the local DC-bus 1 16-1, 116-2, a local AC -bus 118-1, 118-2, and a local controller 120-1, 120-2 are also described in conjunction with FIG. 2. The DFIG based power generation sub systems 102-1, 102-2 may be configured to generate an AC electrical power which may be available at the respective local AC -bus 118-1, 118-2. The AC electrical power generated by each of the DFIG based power generation sub-systems 102-1, l02-2is hereinafter referred to as a local AC power.

[0018] As depicted in FIG. 1, the DFIG based power generation sub-systems 102-1, 102-2 are connected in parallel with each other such that the respective local DC-bus 116-1, 116-2 of the DFIG based power generation sub-systems 102-1, 102-2 is electrically coupled to the reference DC-bus 104. Moreover, in certain embodiments, the respective local AC -buses 118-1, 118-2 of the DFIG based power generation sub-systems 102-1, 102-2 are electrically coupled to the AC distribution bus 106. In the embodiment of FIG. 1, although only two DFIG based power generation sub-systems 102-1, 102- 2 are depicted, the power generation system 100 with more than two such DFIG based power generation sub-systems is also envisioned within the purview of the present patent application.

[0019] In certain embodiments, the DFIG based power generation sub-systems 102-1, 102-2 may be coupled to the reference DC-bus 104 and the AC distribution bus 106 via respective switches 126- 1, 126-2, 128-1, 128-2 as shown in FIG. 1. More particularly, the local DC-bus 116-1, 116-2 of the DFIG based power generation sub-systems 102-1, 102-2 may be coupled to the reference DC-bus 104 respectively via the switch 126-1, 126-2, as depicted in FIG. 1. Similarly, the local AC -bus 118-1, 118-2 of the DFIG based power generation sub-system 102-1, 102-2 may be coupled to the AC distribution bus 106 respectively via the switch 128-1, 128-2, as depicted in FIG. 1. The switches 128- 1, 128-2 may be a multi-phase switch, for example, a three-phase switch. The non-limiting examples of the switches 126-1, 126-2, 128-1, 128-2 include field effect transistors such as metal-oxide- semiconductor field-effect transistors (MOSFETs), gate commutated thyristors, insulated gate bipolar transistors (IGBT), gate turn-off thyristors, static induction transistors, static induction thyristors, or combinations thereof. Furthermore, materials used to form the switches 126-1, 126-2, 128-1, 128-2 may include, but are not limited to, silicon (Si), germanium (Ge), silicon carbide (SiC), gallium nitride (GaN), or combinations thereof.

[0020] In some embodiments, the reference DC-bus 104 may include a plurality of conductors/terminals (not shown in FIG. 1) and one or more capacitors (not shown in FIG. 1) connected between the plurality of conductors/terminals. By way of example, the reference DC-bus 104 may include two conductors/terminals. In such a configuration, while one terminal of the reference DC-bus 104 may be maintained at a positive potential, another terminal of the reference DC- bus 104 may be maintained at a negative potential. In some embodiments, the reference DC-bus 104 may include three conductors/terminals. In such a configuration, while one terminal of the reference DC-bus 104 may be maintained at a positive potential, another terminal may be maintained at a negative potential, and yet another terminal may be maintained at a neutral, for example, zero potential.

[0021] In some embodiments, one or more DC loads may be connected to the reference DC-bus 104 to receive electrical power from the reference DC-bus 104. The DC-load may be any device that operates using a DC power.

[0022] The AC distribution bus 106 may be a single-phase AC -bus or a multi-phase AC -bus, for example, three-phase, AC-bus. The AC distribution bus 106 is coupled to the respective local AC -bus 118-1, 118-2 of the plurality of DFIG based power generation sub-systems 102-1, 102-2. In some embodiments, the AC distribution bus 106 of the power generation system 100 may be connected to an electric grid (not shown in FIG. 1). Such a power generation system 100 sometimes 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 systems for delivering a grid power (e.g., electricity) from one or more power generation stations to consumers through high/medium voltage transmission lines. 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 AC distribution bus 106 of the power generation system 100 may be coupled to an electrical load such as an AC load. The AC load may include one or more devices/equipment that consumes AC power when operated. In certain embodiments, the AC distribution bus 106 may be coupled to both the AC load and the electric grid.

[0023] Moreover, in some embodiments, the auxiliary power source 108 and the energy storage device 110 are coupled to the reference DC-bus 104. The energy storage device 110 may include one or more batteries, capacitors, or a combination thereof. In some embodiments, the auxiliary power source 108 may include a photovoltaic (PV) power source, a fuel cell, a renewable energy based power source, a non-renewable energy based power source, or combinations thereof. The PV power source may include one or more PV arrays, where each PV array may include at least one PV module. A PV module may include a suitable arrangement of a plurality of PV cells. The auxiliary power source 108 may generate a DC power that depends on solar insolation, weather conditions, and/or time of the day. Accordingly, the DC power generated by the auxiliary power source 108 may be supplied to the reference DC-bus 104. In some embodiments, the auxiliary power source 108 and/or the energy storage device 110 are configured to maintain a voltage level of the reference DC-bus 104 above a predetermined threshold value.

[0024] In certain embodiments, the auxiliary power source 108 and the energy storage device 110 may be coupled to the reference DC-bus 104 via respective DC-DC converters 130, 132 to control supply of the electrical power to reference DC-bus 104 and/or to control supply of the electrical power to the energy storage device 110 from the reference DC-bus 104. The DC-DC converter 130, 132 may be operated as a buck converter, a boost converter, or a buck-boost converter, and may be controlled by the supervisory controller 112. Moreover, in the embodiment of FIG. 1, although the power generation system 100 is shown to include one auxiliary power source 108 and one energy storage device 110, the power generation system 100 including more than one auxiliary power sources and energy storage devices is also envisioned.

[0025] The supervisory controller 112 may be operatively coupled to the DFIG based power generation sub-systems 102-1, 102-2, the switches 126-1, 126-2, 128-1, 128-2, and the DC-DC converters 130, 132. In some embodiments, the supervisory controller 112 may be operatively coupled to the local controller 120-1, 120-2 of the DFIG based power generation sub-systems 102-1, 102-2. In the embodiment of FIG. 1, the supervisory controller 112 is shown as operatively coupled to the local controllers 120-1, 120-2, the switches 126-1, 126-2, 128-1, 128-2, and the DC-DC converters 130, 132 via wired control lines (depicted via dashed lines). In some other embodiments, the supervisory controller 112 may be operatively coupled to the local controllers 120-1, 120-2, the switches 126-1, 126-2, 128-1, 128-2, and the DC-DC converters 130, 132 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.

[0026] The supervisory controller 112 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 supervisory controller 112 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 supervisory controller 112 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. [0027] In some embodiments, the supervisory controller 112 may be configured to determine whether there is a mismatch between an AC power requirement of the AC distribution bus 106 and the local AC power available at the local AC -bus 118-1, 118-2 of the plurality of DFIG based power generation sub-systems 102-1, 102-2. The term“AC power requirement” is used to refer to a power demand of the AC load and/or the electric grid coupled to the AC distribution bus 106. The AC power requirement may represent one or more of a magnitude of power (i.e., magnitude/level of voltage and/or current), frequency and phase of the AC power on the AC distribution bus 106. If there is a mismatch between the AC power requirement of the AC distribution bus 106 and the local AC power for given one or more of the DFIG based power generation sub-systems 102-1, 102-2, the supervisory controller 112 may be configured to communicate a synchronization command to the local controller 120-1, 120-2 of the given one or more of the plurality of DFIG based power generation sub-systems 102-1, 102-2. The synchronization command is issued to facilitate synchronization of the local AC power with the AC power requirement of the AC distribution bus 106.

[0028] The synchronization of the local AC power with the AC power requirement of the AC distribution bus 106 may include synchronizing one or more of a frequency and a phase of the local AC power with the frequency and the phase of the AC power on the AC distribution bus 106. Once the local AC power of the DFIG based power generation sub-system 102-1, 102-2 is synchronized with the AC power requirement of the AC distribution bus 106, the supervisory controller 112 may be configured to send control signals to the corresponding switch 128-1, 128-2 to selectively couple the DFIG based power generation sub-system 102-1, 102-2 with the AC distribution bus 106. Further details of the synchronization of the local AC power is described in conjunction with a method described in FIG. 5.

[0029] The power generation system 100 in accordance with some embodiments, facilitate a parallel architecture in which the DFIG based power generation sub-systems 102-1, 102-2 are connected in parallel with each other. By connecting a desired number of the DFIG based power generation sub-systems in parallel, a power generation system 100 with increased rated capacity may be formed. Availability of the reference DC-bus 104 and/or the AC distribution bus 106 provides an easy coupling of DC loads, AC loads, and/or any number of additional power generation sub-systems (see FIG. 3) with the reference DC-bus 104 and/or the AC distribution bus 106. Also, the availability of electrical power at the reference DC-bus results in fast synchronization of the local AC power with the AC power requirement of the AC distribution bus 106.

[0030] Referring now to FIG. 2, a block diagram representation of the DFIG based power generation sub-system 102-1 of FIG. 1 is presented, in accordance with one embodiment of the present specification. As noted earlier, the DFIG based power generation sub-system 102-1 may be configured to generate the local AC power. The DFIG based power generation sub-system 102-1, when coupled to the AC distribution bus 106, provides the local AC power to the AC distribution bus 106 via the local AC -bus 118-1. The local AC power at the local AC -bus 118-1 may be a single phase or multi phase, for example, a three-phase AC power. In some embodiments, the DFIG based power generation sub-system 102-2 may also have a configuration similar to the configuration of the DFIG based power generation sub-system 102-1.

[0031] The DFIG based power generation sub-system 102-1 includes one or more of an engine 202, a DFIG 204, a rotor-side converter 206, a line-side converter 208, the local DC-bus 116-1, the local AC -bus 118-1, the local controller 120-1, and a PCC 210. In some embodiments, the power generation system 100 may optionally include a switching unit 212 disposed between the DFIG 204 and the PCC 210 to selectively couple the DFIG 204 to the PCC 210.

[0032] The local controller 120-1 is operatively coupled to one or more of the engine 202, the rotor- side converter 206, the line-side converter 208, and the switching unit 212 to control operations thereof by communicating appropriate control signals. In the embodiment of FIG. 2, the local controller 120- 1 is operatively coupled to one or more of the engine 202, the rotor-side converter 206, the line-side converter 208, and the switching unit 212 via wired control lines (depicted via dashed lines). In some other embodiments, the local controller 120-1 may be operatively coupled to one or more of the engine 202, the rotor-side converter 206, the line-side converter 208, and the switching unit 212 over the wireless communication medium described earlier. In certain embodiments, the local controller 120- 1 may be configured to control the rotor-side converter 206, the line-side converter 208, an operating speed of the engine 202 based on the synchronization command received from the supervisory controller 112.

[0033] The local controller 120-1 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 local controller 120-1 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 local controller 120-1 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. In some embodiments, the local controller 120-2 of the DFIG based power generation sub-system 102-2 may be similar to the local controller 120-1 of the DFIG based power generation sub-system 102-1. [0034] As depicted in FIG. 2, the DFIG 204 is mechanically coupled to the engine 202. The DFIG 204 is also electrically coupled to the PCC 210 via a link 214 and to the rotor-side converter 206 via a link 216, as depicted in FIG. 2. The line-side converter 208 may be electrically coupled to the PCC 210 via a link 218 as shown in FIG. 2. In some embodiments, the line-side converter 208 is electrically coupled to the PCC 210 via the link 218 through a transformer (not shown in FIG. 2). Each of the links 214, 216, and 218 may be a multi -phase link, for example, a three-phase electrical link as shown in FIG. 2. The PCC 210 may be connected to the local AC -bus 118-1 of the DFIG based power generation sub-system 102-1. In some embodiments, the DFIG based power generation sub-system 102-1 may optionally include a transformer 220. The transformer 220 may be connected between the PCC 210 and the local AC -bus 118-1.

[0035] The engine 202 is coupled to the DFIG 204 and configured to operate the DFIG 204. In particular, the engine 202 may be configured to aid in imparting a rotational motion to a rotary element (e.g., a rotor) of the DFIG 204. The engine 202 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 engine 202 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 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 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 engine 202 employed in the DFIG based power generation sub-system 102-1. Moreover, the engine 202 may be operable at variable speeds, and is also referred to as a“variable speed engine.” In certain embodiments, the engine 202 may be a fixed speed engine.

[0036] The DFIG 204 includes a stator winding 222 and a rotor winding 224. The stator winding 222 may be wound on a stator 226. The rotor winding 224 may be wound on a rotor 228. In some embodiments, both the stator winding 222 and the rotor winding 224 may be multi-phase windings such as a three-phase winding. The DFIG 204 is mechanically coupled to the engine 202 and is operable via the engine 202. For example, the rotor 228 of the DFIG 204 is mechanically coupled to the rotor 228 of the engine 202 via a shaft 230 such that a rotation of the shaft 230 causes a rotation of the rotor 228 of the DFIG 204.

[0037] During an operation of the DFIG based power generation sub-system 102-1, the rotor 228 of the DFIG 204 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 rotary element (e.g., a crankshaft) of the engine 202. The rotational speed of the rotary element of the engine 202 is also hereinafter referred to as an operating speed of the engine 202. In one example, the synchronous speed of the rotor 228 may be defined using equation (1).

r 120 * . ,

N_s = - Equation (1)

P

[0038] In equation (1), N _s represents the synchronous speed of the rotor 228, p represents poles in the rotor 228, and F represents a frequency of a stator voltage. Accordingly, a sub-synchronous speed of the rotor 228 is defined as a speed that is lower than the synchronous speed of the rotor 228. Similarly, a super-synchronous speed of the rotor 228 is defined as a speed that is higher than the synchronous speed of the rotor 228.

[0039] The DFIG 204 is configured to generate an electrical power at the stator winding 222 depending on the rotational speed of the rotor 228. The electrical power that is generated at the stator winding 222 is hereinafter also referred to as a“stator power.” Further, the DFIG 204 is configured to generate or absorb electrical power at the rotor winding 224 depending on the rotational speed of the rotor 228. For example, the DFIG 204 is configured to generate an electrical power at the rotor winding 224 when the rotor 228 is operated at a super-synchronous speed. The DFIG 204 is configured to absorb the electrical power at the rotor winding 224 when the rotor 228 is operated at a sub- synchronous speed. The electrical power that is generated or absorbed at the rotor winding 224 is hereinafter also referred to as a“slip power.” The magnitude of the slip power is dependent on a slip value of the DFIG 204. In one embodiment, the slip value S may be determined using equation (2). Equation (2)

where N_s represents the synchronous speed of the rotor 228 and N_r represents revolutions per minute (rpm) of the rotor 228.

[0040] The rotor-side converter 206 is electrically coupled to the rotor winding 224 of the DFIG 204 via the link 216. The rotor-side converter 206 may be an AC -DC converter and configured to convert an AC power into a DC power and vice-versa. The line-side converter 208 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 rotor-side converter 206 and the line-side converter 208 may include one or more switches, for example, semiconductor switches, configured to facilitate power conversion from AC to DC or vice-versa.

[0041] The rotor-side converter 206 is electrically coupled to the line-side converter 208 via the local DC-bus 116-1. The local DC-bus 116-1 includes a plurality of electrical conductors/terminals and at least one DC-bus capacitor electrically coupled between two conductors/terminals of the local DC-bus 116-1. As previously noted, the reference DC-bus 104 of the power generation system 100 is coupled to the local DC-bus 116-1 of the DFIG based power generation sub-system 102-1.

[0042] In some embodiments, the DFIG based power generation sub-system 102-1 may also include sensors 232. The sensors 232 are disposed at the local AC -bus 118-1. More particularly, each of the sensors 232 may be coupled to one phase line of the local AC -bus 118-1, as depicted in FIG. 2. The sensors 232 may be current sensors, voltage sensor, or combinations thereof. The sensors 232 may be configured to generate electrical signals indicative of voltage and/or current at the respective phase line of the local AC -bus 118-1. The local controller 120-1 may also be operatively coupled to the sensors 232. In the embodiment of FIG. 2, the local controller 120-1 is shown as coupled to the sensors 232 via wired control line (depicted via a dashed line). In some other embodiments, the sensors 232 may be communicatively coupled to the local controller 120-1 over the wireless communication medium described earlier.

[0043] The local controller 120-1 may be configured to receive the electrical signals generated by the sensors 232. Moreover, the local controller 120-1 may determine values of one or more of a voltage and/or current levels of the local AC power at the local AC -bus 118-1, a frequency of the local AC power at the local AC -bus 118-1, and a phase of the local AC power at the local AC -bus 118-1. The local controller 120-1 may communicate the values of the determined one or more of the voltage and/or current levels of the local AC power at the local AC -bus 118-1, the frequency of the local AC power at the local AC -bus 118-1, and the phase of the local AC power at the local AC -bus 118-1 to the supervisory controller 112.

[0044] In certain embodiments, the local controller 120-1 may function under a supervisory control of the supervisory controller 112. For example, the local controller 120-1 is configured to receive the synchronization command from the supervisory controller 112 if the local AC power of the DFIG based power generation sub-system 102-1 is not matching with the AC power requirements of the AC distribution bus 106. Accordingly, the local controller 120-1 may be configured to control at least one of the rotor-side converter 206, the line-side converter 208, and the operating speed of the engine 202 such that an electrical power is drawn by the DFIG 204 from the reference DC-bus 104 or the electrical power is supplied by the DFIG 204 to the reference DC-bus 104.

[0045] FIG. 3 is a block diagram representation of a power generation system 300, in accordance with one embodiment of the present specification. The power generation system 300 of FIG. 3 includes certain elements that are similar to the elements of the power generation system 100 of FIG. 1, description of which is not repeated herein. In comparison to the power generation system 100 of FIG. 1, the power generation system 300 includes one or more additional power generation sub systems 302, 304. Although FIG. 3 is shown to include both the power generation sub-systems 302, 304, it may be noted that one of the power generation sub-systems 302, 304 may also be used. Moreover, more than two such power generation sub-systems 302, 304 may also be employed depending on power demand and design considerations. The supervisory controller 112 may be operatively coupled to the additional power generation sub-systems 302 and/or 304.

[0046] In some embodiments, the additional power generation sub-system such as the power generation sub-system 302 may be coupled to the reference DC-bus 104 directly or via a switch (not shown in FIG. 3). The power generation sub-system 302 may include a fixed speed engine 306, a generator 308, and an AC -DC converter 310. In some embodiments, the fixed speed engine 306 may be similar to the engine 202 of the DFIG based power generation sub-system 102-1 or 102-2 except the fact that the engine 306 may be operated at a fixed speed. The generator 308 is mechanically coupled to and operated via the fixed speed engine 306. The generator 308 may be representative of a synchronous or an asynchronous generator that is configured to generate AC power. The AC -DC converter 310 may be representative of a known power converter. The AC -DC converter 310 is coupled to the generator 308 to receive the AC power and configured to convert the AC power received from the generator 308 to a DC power. Moreover, an output of the AC -DC converter 310 is coupled to the reference DC-bus 104, as depicted in FIG. 3.

[0047] During operation of the power generation system 300, the supervisory controller 112 may be configured to determine if a voltage level of the reference DC-bus 104 is below a predetermined threshold value and the DC power supplied from the auxiliary power source 108 and the energy storage device 110 is insufficient to maintain a voltage level of the reference DC-bus 104 above the predetermined threshold value. If it is determined that the DC power supplied from the auxiliary power source 108 and the energy storage device 110 is insufficient to maintain the voltage level of the reference DC-bus 104 above the predetermined threshold value, the supervisory controller 112 may selectively operate the additional power generation sub-system 302 to generate the DC power such that the voltage level of the reference DC-bus 104 is maintained above the predetermined threshold value. More particularly, the supervisory controller 112 may be configured to selectively operate the fixed speed engine 306 of the additional power generation sub-system 302 to maintain the voltage level of the reference DC-bus 104 above the predetermined threshold value. In some embodiments, to start operating the fixed speed engine 306, the supervisory controller 112 may be configured to operate the generator 308 as a motor using the electrical power from the reference DC-bus 104. Consequently, the fixed speed engine 306 may be cranked / started by the generator 308 operating as motor. Once the fixed speed engine 306 is started, the generator 308 may not be operated as motor. In fact, once the fixed speed engine 306 is started, the fixed speed engine 306 may be configured to rotate a rotor (not shown) of the generator 308, thereby operating the generator 308 to produce electrical power. [0048] In certain embodiments, alternatively or additionally, the power generation sub-system 304 may be coupled to the AC distribution bus 106 directly or via a switch (not shown in FIG. 3). The power generation sub-system 304 may include one or more components similar to the power generation sub-system 302. In comparison to the power generation sub-system 302, the power generation sub-system 304 does not require to include the AC -DC converter 310 as the power generation sub-system 304 is electrically coupled to the AC distribution bus 106. Accordingly, the power generation sub-system 304 includes a fixed speed engine 312 similar to the fixed speed engine 306 and a generator 314 similar to the generator 308. The generator 314 is mechanically coupled to and operated via the fixed speed engine 312. An output of the generator 314 is connected to the AC distribution bus 106. When operated, the generator 314 generates an AC power.

[0049] During operation of the power generation system 300, the supervisory controller 112 may be configured to determine if a total power demand at the AC distribution bus 106 and the reference DC-bus 104 is higher than a total rated capacity of the DFIG based power generation sub-systems 102- 1, 102-2. If it is determined that the total power demand at the AC distribution bus 106 and the reference DC-bus 104 is higher than the total rated capacity of the DFIG based power generation sub systems 102-1, 102-2, the supervisory controller 112 may be configured to operate one or both the power generation sub-systems 302, 304 to supply an electrical power to meet an additional power demand. In some embodiments, to start operating the fixed speed engine 312, the supervisory controller 112 may be configured to operate the generator 314 as a motor using the electrical power from the AC distribution bus 106. Consequently, the fixed speed engine 312 may be cranked / started by the generator 314 operating as motor. Once the fixed speed engine 312 is started, the generator 314 may not be operated as motor. In fact, once the fixed speed engine 312 is started, the fixed speed engine 312 may be configured to rotate a rotor (not shown) of the generator 314, thereby operating the generator 314 to produce electrical power necessary to the meet additional power demand.

[0050] FIG. 4 is a flow diagram of a method 400 for forming a power generation system such as the power generation systems 100, 300, in accordance with one embodiment of the present specification. The method 400 is described in conjunction with FIGs. 1-3.

[0051] At step 402, a reference DC-bus, such as, the reference DC-bus 104 as shown in FIGs. 1 and 3, is provided. Further, at step 404, the plurality of DFIG based power generation sub-systems 102-1, 102-2 is electrically coupled to the reference DC-bus 104. As depicted in FIGs. 1 and 3, the plurality of DFIG based power generation sub-systems 102-1, 102-2 are coupled to the reference DC- bus 104 via respectively switches 126-1, 126-2. More particularly, the plurality of DFIG based power generation sub-systems 102-1, 102-2 may be electrically coupled to the reference DC-bus 104 such that the local DC-bus 116-1, 116-2 of the plurality of DFIG based power generation sub-systems 102- 1, 102-2 is coupled to the reference DC-bus 104 via the respective switches 126-1, 126-2.

[0052] Further, at step 406, the auxiliary power source 108 and the energy storage device 110 are electrically coupled to the reference DC-bus 104. In some embodiments, the auxiliary power source 108 and the energy storage device 110 may be coupled directly to the reference DC-bus 104. In certain other embodiments, the auxiliary power source 108 and the energy storage device 110 may be electrically coupled to the reference DC-bus 104 via DC-DC converter 130, 132, respectively.

[0053] Furthermore, at step 408, an additional power generation sub-system such as the additional power generation sub-system 302 may be electrically coupled to the reference DC-bus 104. More particularly, an output of the AC -DC converter 310 of the additional power generation sub-system 302 is electrically coupled to the reference DC-bus 104. In certain embodiments, the additional power generation sub-system 302 may be configured to maintain the voltage level of the reference DC-bus 104 above the predetermined threshold value in instances where the electrical power from the auxiliary power source 108 and the energy storage device 110 is insufficient to maintain the voltage level of the DC-bus above the predetermined threshold value.

[0054] Moreover, at step 410, the local AC -bus 118-1, 118-2 of one or more of the plurality of DFIG based power generation sub-systems 102-1, 102-2 is electrically coupled to the AC distribution bus 106. In certain embodiments, the supervisory controller 112 facilitates such electrical coupling of the plurality of DFIG based power generation sub-systems 102-1, 102-2 with the AC distribution bus 106 when the local AC power at the local AC -bus 118-1, 118-2 is synchronized with the AC power requirement of the AC distribution bus 106. Details of synchronizing the local AC power with the AC power requirement of the AC distribution bus 106 is described in conjunction with FIG. 5.

[0055] Additionally, in certain embodiments, the method 400, at step 412, includes electrically coupling an additional power generation sub-system such as the power generation sub-system 304 to the AC distribution bus 106. In certain embodiments, the power generation sub-system 304 aids in sharing a power demand on the AC distribution bus 106. In some embodiments, the power generation sub-system 304 may be selectively operated by the supervisory controller 112 to meet the power demand on the AC distribution bus 106 when the power demand increases beyond a predefined level. The predefined level, in some embodiments, may be equivalent to a sum of a rated capacity of the plurality of DFIG based power generation sub-systems 102-1, 102-2.

[0056] FIG. 5 is a flow diagram of a method 500 for operating a power generation system such as the power generation system 100, in accordance with one embodiment of the present specification. The method 500 is described in conjunction with FIGs. 1-3. [0057] The method 500, at step 502, includes receiving information regarding the local AC power generated by the plurality of DFIG based power generation sub-systems 102-1, 102-2 by the supervisory controller 112. In some embodiments, the supervisory controller 112 may periodically receive the information regarding the local AC power from the local controllers 120-1, 120-2. In certain other embodiments, the supervisory controller 112 may send a signal to the local controllers 120-1, 120-2 requesting the information regarding the respective local AC power. In response, the supervisory controller 112 receives the information regarding the respective local AC power from the local controllers 120-1, 120-2. The information regarding the respective local AC power may include values of one or more of the voltage and/or current levels, the frequency, and the phase of the local AC power at the local AC -bus 118-1, 118-2. As previously noted, the values of the voltage and/or current levels, the frequency, and the phase of the local AC power at the local AC -bus 118-1, 118-2 are determined by the respective local controller 120-1, 120-2 based on signals received from the sensors 232.

[0058] Further, at step 504, the supervisory controller 112 is configured to perform a check to determine whether there is a mismatch between the AC power requirement of the AC distribution bus 106 and the local AC power generated by the plurality of DFIG based power generation sub-systems 102-1, 102-2. To determine whether there is a mismatch between the AC power requirement of the AC distribution bus 106 and the local AC power, the supervisory controller 112 may compare the values of one or more of the voltage and/or current levels, the frequency, and the phase of the local AC power with corresponding AC power requirement of the AC distribution bus 106. If the values of the voltage and/or current levels, the frequency, and the phase of the local AC power are same as the corresponding AC power requirement of the AC distribution bus 106, or within a predefined tolerance with respect to the corresponding AC power requirement of the AC distribution bus 106, the supervisory controller 112 may conclude that there is no mismatch between the AC power requirement of the AC distribution bus 106 and the local AC power. However, if the values of the voltage and/or current levels, the frequency, and the phase of the local AC power are not same as the corresponding AC power requirement of the AC distribution bus 106 or not within a predefined tolerance from the corresponding AC power requirement of the AC distribution bus 106, the supervisory controller 112 may determine that there is a mismatch between the AC power requirement of the AC distribution bus 106 and the local AC power.

[0059] At step 504, if it is determined that there is no mismatch between the AC power requirement of the AC distribution bus 106 and the local AC power, the supervisory controller 112, an execution of the method may loop back to step 502 where the supervisory controller 112 may be configured to receive the information regarding the local AC power generated by the DFIG based power generation sub-systems 102-1, 102-2.

[0060] At step 504, if it is determined that there is a mismatch between the AC power requirement of the AC distribution bus 106 and the local AC power, the supervisory controller 112, at step 506, communicates a synchronization command to the local controller 120-1, 120-2 of one or more of the plurality of DFIG based power generation sub-systems 102-1, 102-2 for which there exists the mismatch between the AC power requirement of the AC distribution bus 106 and the local AC power. The synchronization command is issued by the supervisory controller 112 to enable synchronization of the local AC power of the one or more of the plurality of DFIG based power generation sub-systems 102-1, 102-2 with the AC power requirement of the AC distribution bus 106.

[0061] Moreover, at step 508, the local controller 120-1, 120-2 receives the synchronization command from the supervisory controller 112. In response to the synchronization command, the local controller 120-1, 120-2, at step 510, synchronizes the local AC power of the respective DFIG based power generation sub-system 102-1, 102-2 with the AC power requirement of the AC distribution bus 106. In some embodiments, the synchronization of the local AC power may include modifying the local AC power such that values of one or more of the voltage and/or current levels, the frequency, and the phase of the local AC power at the local AC -bus 118-1, 118-2 is equal to the voltage and/or current levels, a frequency, and a phase of the AC power on the AC distribution bus 106. In some embodiments, the synchronization of the local AC power may include modifying the AC power such that values of one or more of the voltage and/or current levels, the frequency, and the phase of the local AC power at the local AC -bus 118-1, 118-2 are within the predefined tolerance from the voltage and/or current levels, the frequency, and the phase of the AC power on the AC distribution bus 106.

[0062] To effect the synchronization of the local AC power with the AC power requirement of the AC distribution bus 106, the local controller 120-1, 120-2 may be configured to control respective at least one of the line-side converter 208, the rotor-side converter 206, and the operating speed of an engine 202 such that an electrical power is drawn by the DFIG 204 from the reference DC-bus 104 or the electrical power is supplied by the DFIG 204 to the reference DC-bus 104.

[0063] In some embodiments, the electrical power is drawn by the DFIG 204 from the reference DC-bus 104 via the rotor-side converter 206 and the local DC-bus 116-1 or 116-2 effect the synchronization. In some embodiments, when the electrical power is required to be drawn by the DFIG 204 from the reference DC-bus 104, at least a portion of the electrical power is supplied to the reference DC-bus 104 by an auxiliary power source 108. If the portion of the electrical power supplied by the auxiliary power source 108 is less than a requirement of the electrical power by the DFIG 204 from the reference DC-bus 104, an additional electrical power to the reference DC-bus 104 may be supplied to the reference DC-bus 104 from the energy storage device 110 to fulfill the requirement of the electrical power by the DFIG 204. In certain embodiments, if a sum of the electrical power supplied from both the auxiliary power source 108 and the energy storage device 110 is less than the requirement of the electrical power by the DFIG 204 from the reference DC-bus 104, the supervisory controller 112 may be configured to operate an additional power generation sub-system such as the power generation sub-system 302, as shown in FIG. 3. Consequently, a desired additional electrical power may be supplied by the power generation sub-system 302 to the reference DC-bus 104 to fulfill the requirement of the electrical power by the DFIG 204 from the reference DC-bus 104.

[0064] In certain embodiments, the electrical power is supplied by the DFIG 204 to the reference DC-bus 104 via the rotor-side converter 206 and the local DC-bus 116-1 or 116-2 effect the synchronization. When the electrical power is required to be supplied from the DFIG 204 to the reference DC-bus 104, the energy storage device 110 may be configured to store at least a portion or all of the electrical power supplied to the reference DC-bus 104 from the DFIG 204. In certain embodiments, at least some portion of the electrical power supplied to the reference DC-bus 104 may also be consumed by the DC-load (not shown in FIGs. 1 and 3) connected to the reference DC-bus 104.

[0065] 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.

[0066] In accordance with some embodiments described herein, a power generation systems 100, 300 are provided. The power generation systems 100, 300 in accordance with some embodiments, facilitate a parallel architecture in which the DFIG based power generation sub-systems 102-1, 102-2 are connected in parallel with each other. By connecting a desired number of the DFIG based power generation sub-systems 102-1, 102-2 in parallel, a power generation system 100, 300 with increased rated capacity may be formed. The DFIG based power generation sub-systems 102-1, 102-2 are operated by a variable speed engine such the engine 202. Use of the variable speed engine 202 improves overall efficiency of the DFIG based power generation sub-systems 102-1, 102-2 and hence the efficiency of the power generation systems 100, 300 is also improved. Due to the improved efficiency of the power generation systems 100, 300, fuel consumption by the power generation systems 100, 300 may also be reduced.

[0067] Furthermore, the DFIG based power generation sub-systems 102-1, 102-2 are connected in parallel with each other via the reference DC-bus 104 and/or the AC distribution bus 106. Advantageously, availability of such reference DC-bus 104 and/or the AC distribution bus 106 provides an easy coupling of DC loads and AC loads respectively with the reference DC-bus 104 and/or the AC distribution bus 106. Also, the availability of electrical power at the reference DC-bus results in fast synchronization of the local AC power with the AC power requirement of the AC distribution bus 106.

[0068] Moreover, additional power generation sub-systems such as the power generation sub- systems 302, 304 may also be connected in the power generation system 300 leading to further enhancement in the rated capacity of the power generation system. The power generation sub-systems 302 may aid in maintaining voltage level of the reference DC-bus 104 when the electrical power from the auxiliary power source 108 and the energy storage device 110 is insufficient. Advantageously, a live DC-link such as the reference DC-bus 104 may be provided. Provision of such live reference DC- bus 104 may improve reliability of the power generation sub-systems 302, 304.

[0069] 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

CLAIMS WE CLAIM

1. A power generation system (100, 300), comprising:

a reference direct current (DC) bus (104);

a plurality of doubly-fed induction generator (DFIG) based power generation sub-systems (102-1, 102-2) electrically coupled in parallel with each other via the reference DC-bus (104), wherein each of the plurality of DFIG based power generation sub-systems (102-1, 102-2) comprises a DFIG (204), a rotor-side converter (206) and a line-side converter (208) coupled to the DFIG (204), wherein the line-side converter (208) and the rotor-side converter (206) are electrically coupled to each other via a local DC-bus (116-1, 116-2), and wherein the local DC-bus (116-1, 116-2) of each of the plurality of DFIG based power generation sub-systems (102-1, 102-2) is coupled to the reference DC-bus (104); and

an auxiliary power source (108) and an energy storage device (110) electrically coupled to the reference DC-bus (104).

2. The power generation system (100, 300) as claimed in claim 1, wherein one or more of the plurality of DFIG based power generation sub-systems (102-1, 102-2) comprise an engine (202) coupled to the DFIG (204) and configured to operate the DFIG (204), wherein the engine (202) is operated at a variable speed.

3. The power generation system (100, 300) as claimed in claim 2, wherein each of the plurality of DFIG based power generation sub-systems (102-1, 102-2) comprises a local controller (120-1, 120-2) operatively coupled to the engine (202), the line-side converter (208), and the rotor- side converter (206).

4. The power generation system (100, 300) as claimed in claim 3, comprising a supervisory controller (112) operatively coupled to the local controller (120-1, 120-2) of each of the plurality of DFIG based power generation sub-systems (102-1, 102-2).

5. The power generation system (100, 300) as claimed in claim 4, comprising an AC distribution bus (106) coupled to a local alternating current (AC) bus (118-1, 118-2) of each of the plurality of DFIG based power generation sub-systems (102-1, 102-2) via a switch (128-1, 128-2), wherein the DFIG (204) comprises a stator winding (222) and a rotor winding (224), wherein the stator winding (222) is electrically coupled to the line-side converter (208) and the local AC -bus (118-1, 118- 2), and wherein the rotor winding (224) is electrically coupled to the rotor-side converter (206).

6. The power generation system (300) as claimed in claim 5, comprising an additional power generation sub-system (304) electrically coupled to the AC distribution bus (106), wherein the additional power generation sub-system (304) comprises a fixed speed engine (312) and a generator (314) mechanically coupled to the fixed speed engine (312).

7. The power generation system (100, 300) as claimed in claim 5, wherein the supervisory controller (112) is configured to:

determine whether there is a mismatch between an AC power requirement of the AC distribution bus (106) and a local AC power at the local AC -bus (118-1, 118-2) of each of the plurality of DFIG based power generation sub-systems (102-1, 102-2); and

communicate, in response to determining the mismatch, a synchronization command to the local controller (120-1, 120-2) of corresponding one or more of the plurality of DFIG based power generation sub-systems (102-1, 102-2) to synchronize the local AC power with the AC power requirement of the AC distribution bus (106).

8. The power generation system (100, 300) as claimed in claim 7, wherein, to synchronize the local AC power with the AC power requirement of the AC distribution bus (106), the local controller (120-1, 120-2) of the corresponding one or more of the plurality of DFIG based power generation sub-systems (102-1, 102-2) is configured to control one or more of the line-side converter (208), the rotor-side converter (206), and an operating speed of the engine (202) such that an electrical power is drawn by the DFIG (204) from the reference DC-bus (104) or the electrical power is supplied by the DFIG (204) to the reference DC-bus (104).

9. The power generation system (100, 300) as claimed in claim 8, wherein the auxiliary power source (108) is configured to supply at least a portion of the electrical power to the reference DC-bus (104).

10. The power generation system (100, 300) as claimed in claim 8, wherein the energy storage device (110) is configured to supply at least a portion of the electrical power to the reference DC-bus (104) or store at least the portion of the electrical power from the reference DC-bus (104).

11. The power generation system (300) as claimed in claim 1, comprising an additional power generation sub-system (302) electrically coupled to the reference DC-bus (104), wherein the additional power generation sub-system (302) comprises a fixed speed engine (306), a generator (308) mechanically coupled to the fixed speed engine (306), and a DC-DC converter (310) coupled to an output of the generator (308).

12. The power generation system (100, 300) as claimed in claim 1, wherein the auxiliary power source (108) comprises a photovoltaic (PV) power source, a fuel cell, a renewable energy based power source, a non-renewable energy based power source, or combinations thereof.

13. A method (500) for operating a power generation system (100, 300) comprising a plurality of doubly-fed induction generator (DFIG) based power generation sub-systems (102-1, 102- 2) coupled in parallel to each other via a reference direct current (DC) (104) bus and an alternating current (AC) distribution bus (106), the method (500) comprising:

determining whether there is a mismatch between an AC power requirement of the AC distribution bus (106) and a local AC power generated by the plurality of DFIG based power generation sub-systems (102-1, 102-2); and

communicating, in response to determining the mismatch, synchronization command to a local controller (120-1, 120-2) of corresponding one or more of the plurality of DFIG based power generation sub-systems (102-1, 102-2) to enable synchronization of the local AC power of the one or more of the plurality of DFIG based power generation sub-systems (102-1, 102-2) with the AC power requirement of the AC distribution bus (106), wherein each of the plurality of DFIG based power generation sub-systems (102-1, 102-2) comprises a DFIG (204), a rotor-side converter (206) and a line-side converter (208) coupled to the DFIG (204), wherein the line-side converter (208) and the rotor-side converter (206) are electrically coupled to each other via a local DC-bus (116-1, 116-2), wherein the local DC-bus (116-1, 116-2) of each of the plurality of DFIG based power generation sub systems (102-1, 102-2) is coupled to the reference DC-bus (104), and wherein the local controller (120- 1, 120-2) is operatively coupled to the line-side converter (208) and the rotor-side converter (206).

14. The method (500) as claimed in claim 13, comprising synchronizing the local AC power of one or more of the plurality of DFIG based power generation sub-systems (102-1, 102-2) with the AC power requirement of the AC distribution bus (106).

15. The method (500) as claimed in claim 14, wherein synchronizing the respective local AC power comprises controlling at least one of the line-side converter (208), the rotor-side converter (206), and an operating speed of an engine (202) such that an electrical power is drawn by the DFIG (204) from the reference DC-bus (104) or the electrical power is supplied by the DFIG (204) to the reference DC-bus (104), wherein the engine (202) is mechanically coupled to the DFIG (204).

16. The method (500) as claimed in claim 15, further comprising supplying at least a portion of the electrical power to the reference DC-bus (104) by an auxiliary power source (108) if the electrical power is required to be drawn by the DFIG (204) from the reference DC-bus (104), wherein the auxiliary power source (108) is electrically coupled to the reference DC-bus (104).

17. The method (500) as claimed in claim 16, further comprising supplying an additional electrical power to the reference DC-bus (104) by an energy storage device (110) if electrical power supplied from the auxiliary power source (108) is less than a requirement of the electrical power by the DFIG (204) from the reference DC-bus (104), wherein the energy storage device (110) is electrically coupled to the reference DC-bus (104).

18. The method (500) as claimed in claim 17, further comprising supplying a desired additional electrical power to the reference DC-bus (104) by an additional power generation sub- system (302) electrically coupled to the reference DC-bus (104) if a sum of the electrical power supplied from the auxiliary power source (108) and the energy storage device (110) is less than the requirement of the electrical power by the DFIG (204) from the reference DC-bus (104).

19. The method (500) as claimed in claim 15, further comprising storing at least a portion of the electrical power from the reference DC-bus (104) by an energy storage device (110) if the electrical power is required to be supplied from the DFIG (204) to the reference DC-bus (104), wherein the energy storage device (110) is electrically coupled to the reference DC-bus (104).