1. An inverter used for Direct Current (DC) bus utilization, comprising: a first inverter and a second inverter, electrically coupled back to back through primary winding of an electric transformer and a DC link capacitor connected to a power source in parallel with the inverter for adjusting waveform of signal output through the power source, wherein the inverter is electrically coupled to a grid through secondary winding of the electric transformer.

2. The inverter as claimed in claim 1, wherein arms of same phase of the first inverter and the second inverter are connected to each ends of the primary winding of the electric transformer.

3. A system used for Direct Current (DC) bus utilization, comprising: a power source to provide a DC; and an inverter comprising, a first inverter and a second inverter, electrically coupled back to back through primary winding of an electric transformer and a DC link capacitor connected to the power source in parallel with the inverter for adjusting waveform of signal output through the power source, wherein the inverter is electrically coupled to a grid through secondary winding of the electric transformer.

4. The system as claimed in claim 3, wherein the power source is a wind turbine with a Doubly Fed Induction Generator (DFIG) coupled to a converter to provide the DC.

5. The system as claimed in claim 4, wherein a rotor of the DFIG is electrically connected to the converter and a stator of the DFIG is electrically connected to a grid.

6. The system as claimed in claim 3, wherein the power source is a wind turbine coupled with an asynchronous machine and electrically connected to a converter to provide the DC.

7. The system as claimed in claim 3, wherein the power source is a wind turbine coupled with a synchronous machine and electrically connected to a converter to provide the DC.

8. The system as claimed in claim 3, wherein the power source is solar photo voltaic electrically coupled to a converter to provide the DC.

9. A wind power generation system, comprising the system used for DC bus utilization according to claim 3.

10. A solar power generation system, comprising the system used for DC bus utilization according to claim 3.

11. A method for Direct Current (DC) bus utilization, comprising acts of: providing a DC from a power source; converting the DC to a fixed AC by an inverter comprising, a first inverter and a second inverter, electrically coupled back to back through a primary winding of an electric transformer; and supplying the fixed AC to a grid, electrically coupled to a secondary winding of the electric transformer.

12. The method as claimed in claim 9, wherein the inverter comprises of switches whose operation can be controlled in at least one of the first inverter and the second inverter to suppress a circulating current while supplying the fixed AC to the grid.

13. The method as claimed in claim 10, wherein the operation of the switches in the first inverter is controlled to supress the circulating current by maintaining a predefined position of the switches in the second inverter.

14. A method for wind power generation system, comprising the method for DC bus utilization according to claim 9.

15. A method for solar power generation system, comprising the method for DC bus utilization according to claim 9. ,TagSPECI:TECHNICAL FIELD The present disclosure generally relates to an area of power electronics. The disclosure discloses embodiments of a device, system and method for an improved Direct Current (DC) bus utilization. BACKGROUND Presently, a renewable power generation system consists of a power source including a converter which converts variable frequency into DC, a DC link capacitor, an inverter electrically coupled to a grid via a transformer. The inverter, electrically coupled with the grid, converts the DC which is provided by the power source to a fixed alternate current (AC). The DC link capacitor is electrically coupled in parallel between the power source and the inverter. The inverter along with the DC link capacitor provides a real power and a reactive power according to the demands of the grid. Control of the reactive power of the inverter is more crucial in order to balance a voltage stability of the power generation system. Also, the power generation system should be in synchronization with the grid during fault condition according to a defined requirement of a low voltage ride through (LVRT) grid code standard. However for a given DC bus voltage; there exist a limitation in the existing power generation system because of constraints with respect to topology of the inverter and variations in the power source. Figure 1 shows an exemplary prior art embodiment of a wind power generation system (100). The system (100) consists of a power source (101), a DC link capacitor (108) and an inverter (109) which is electrically coupled with a grid (111) via an electric transformer and a filter (110). Further, the power source (101) consists of a wind turbine (102), a gear box (103), a generator (104) and an AC to DC converter (107). The generator (104) is a synchronous machine or an asynchronous machine and only stator (106) of the generator (104) is connected to the converter (107). Further, the wind turbine (101), the gear box (102) and the generator (103) are mechanically coupled and convert wind energy to electrical energy which is in form of a variable AC which is further converted to DC by the converter (107). . Further, the inverter in the system (100) converts the DC into a fixed AC and feds to the grid. Figure 2 shows another exemplary prior art embodiment of a wind power generation system (200). The system (200) consists of a power source (101), a DC link capacitor (108) and a grid side converter (205) which is electrically coupled with a grid (111) via an electric transformer and a filter (110). Further, the power source (101) consists of a wind turbine (102), a gear box (103), a doubly fed induction generator (DFIG) (201) and a rotor side converter (204). The wind turbine (102), the gear box (103) and the DFIG (201) are mechanically coupled and convert wind energy to electrical energy which is in form of a variable AC. A rotor (202) of the DFIG (201) is connected to the rotor side converter (204) wherein a stator (203) of the DFIG is connected to the grid (111) directly. Further as illustrated with respect to Figure 1, at super synchronous speed the variable AC is converted to DC by the rotor side converter (204) and the DC is converted to a fixed AC by the grid side converter which is fed to the grid (111). But at sub synchronous speed the fixed AC is converted to DC by the grid side converter (205) and the DC is converted to a variable AC by the rotor side converter (204). Further, Figure 3 shows an exemplary prior art embodiment of a solar power generation system (300). The system (300) consists of a power source (101), a DC link capacitor (108) and an inverter (109) which is electrically coupled with a grid (111) via an electric transformer and a filter (110). Further, the power source (101) consists of photo voltaic cells (301) and a DC to DC converter (302). The photo voltaic cells (301) together with the DC to DC converter that is the power source (101) convert solar energy to electrical energy which is in form of a DC. The inverter (109) converts the DC to a fixed AC which is further fed to the grid (111). However, in order to feed a power into the grid (111) by the inverter (109) as illustrated in the exemplary embodiments in Figure 1, Figure 2 and Figure 3, the inverter (109) must always be maintained at a fixed frequency of 50 Hz and at a defined grid voltage. But voltages from the power source (101) is of variable frequencies which depends upon wind speed in the wind power generation system and depends on voltage drop across the photo voltaic cells in the solar power generation system. Therefore, in order to get the fixed frequency of 50 Hz and required voltages at the inverter (109), voltages with variable frequencies from the power source (101) are converted to DC using converters and then to fixed AC by the inverter (109). In this conventional process of converting the variable AC to DC and DC to a fixed AC, DC bus voltage (Vdc) has to be maintained at a defined value to feed energy into grid (111) with improved power quality. The available DC link capacitor (107) voltage mainly depends upon the availability of the power at power source and power source configuration. Whereas the maintenance is tough when the DC bus voltage is lesser than the defined value and thereby the power fed to the grid will be affected which is a limitation with regard to conventional systems. Further, for the existing inverter (109) implemented in any power generation system, the maximum of phase voltage occurs in the inverter that is the DC bus utilization happens only for 2/3 (Vdc) and also zero sequence voltage (ZSV) occurs only for a single switching state of the inverter (109). Further to this, there arises circulating current in the inverter of the system which is impractical to suppress with the existing inverter (109) switching which is another limitation of the conventional systems. Accordingly, a need exists for a system to improve the DC bus utilization and to overcome one or more limitations stated above. SUMMARY One or more shortcomings of the prior art are overcome and additional advantages are provided through the present disclosure. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure. The present disclosure proposes a new topology for an inverter for DC bus utilization. The inverter comprises of a first inverter and a second inverter which are electrically coupled back to back through primary winding of an electric transformer and a DC link capacitor is connected to a power source in parallel with the inverter for adjusting waveform of signal output through the power source. The inverter is electrically coupled to a grid through secondary winding of the electric transformer. Further, the present disclosure proposes a system for DC bus utilization, comprising of a power source to provide a DC to the proposed new topology of the inverter. The DC is converted to a fixed AC by the inverter and supplies the fixed AC to the grid. Also, the present disclosure proposes a method in the system used for DC bus utilization, which involves in providing the DC by the power source to the inverter through a DC link capacitor. The inverter converts the DC to fixed AC and feeds it the grid through the electric transformer. The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects and features described above, further aspects, and features will become apparent by reference to the drawings and the following detailed description. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate exemplary embodiments and, together with the description, serve to explain the disclosed principles. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system and/or methods in accordance with embodiments of the present subject matter are now described, by way of example only, and with reference to the accompanying figures, in which: Figure 1 illustrates an embodiment of a conventional wind power generation system; Figure 2 illustrates another embodiment of a conventional wind power generation system; Figure 3 illustrates an embodiment of a conventional solar power generation system; Figure 4 illustrates an exemplary embodiment of a wind application with a synchronous machine in accordance with the present disclosure; Figure 5 illustrates an exemplary embodiment of a wind application with a doubly fed induction generator (DFIG) in accordance with the present disclosure; Figure 6 illustrates an exemplary embodiment of a solar application in accordance with the present disclosure; Figure 7 illustrates a plot representing a space vector representation of PWM, in accordance with the present disclosure; It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative systems embodying the principles of the present subject matter. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and executed by a computer or processor, whether or not such computer or processor is explicitly shown. DETAILED DESCRIPTION The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the claims of the disclosure. It should be appreciated by those skilled in the art that the conception and specific aspect disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. In the present document, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the disclosure. The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a system or apparatus proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or apparatus. Embodiments of the present disclosure relates to a new topology of an inverter used for DC bus utilization. The inverter comprises of a first inverter and a second inverter which are electrically coupled back to back through primary winding of an electric transformer and a DC link capacitor connected to a power source in parallel with the inverter for adjusting waveform of signal output through the power source. Further, the inverter is electrically coupled to a grid through secondary winding of the electric transformer. Also, the present disclosure relates to a system used for DC bus utilization which consists of a power source to provide a DC, said new topology of the inventor and a DC link capacitor connected to the power source in parallel with the inverter. Also, the present disclosure relates to a method for DC bus utilization which involves in providing a DC from a power source to the inverter which converts the DC to a fixed AC and supplying the fixed AC to a grid, electrically coupled to a secondary winding of the electric transformer. In the following detailed description of the embodiments of the disclosure, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, not to be taken in a limiting sense. Figure 4 illustrates an exemplary embodiment of a wind application with a generator in accordance with the present disclosure. As shown in Figure 4, the wind power generation system (400) converts wind energy to an electrical energy. The wind power generation system (400) consists of a power source (401), a DC link capacitor (408) and an inverter (409). The inverter (409) has a modified topology with respect to an inverter existing in any conventional systems. Further, the power source (401) consists of a wind turbine (402), a gear box (403), a generator (404) and a converter (407). The generator in the system (400) may be a synchronous machine. Stator (406) of the generator (404) is connected to the converter (407). Further, the DC link capacitor (408) is connected in parallel between the converter (407) and the inverter (409) in the power generation system (400). The inverter unit (409) consist of two inverters, a first inverter (410) and a second inverter (411), connected via a transformer (412). In the power generation system (400), configuration of the first inverter with a–phase, b-phase and c-phase arms is represented with a, b and c respectively and corresponding switching states represented as Sa, Sb and Sc respectively. Similarly, configuration of the second inverter with a-phase, b-phase and c-phase arms is represented with a’, b’ and c’ respectively and corresponding switching states are represented with Sa’, Sb’ and Sc’ respectively. An upper switch and a lower switch of each arm (a, b, c, a’, b’ and c’) of the inverter, are complementary to each other. Each side of primary winding of the transformer (611) is connected to each arm of the inverter of same phase and the secondary winding of the transformer (611) is connected to the grid (614) via a filter (413). The filter (413) is used to process the waveform and separate the unwanted frequencies from the desired waveform. This connection between the inverter (409) and the grid (414) via the transformer (412) and the filter (413) is illustrated in Figure 4. Further, the power source provides electrical energy in the form of a DC. The inverter (409) converts the DC which is one of a fixed DC or a variable DC into a fixed AC and is fed to the grid (414) via a filter (413). Figure 5 illustrates a wind application system with a doubly fed induction generator (DFIG) in accordance with one embodiment of the present disclosure. As shown in Figure 5, the wind power generation system (500) comprises a power source (401), a DC link capacitor (408) and a grid side converter (505) connected to a grid (414) via a filter (413). Further, the power source (401) consists of a wind turbine (402), electrically coupled with a DFIG (501) and a rotor side converter (504). Further, rotor (502) of the DFIG (501) is connected to the rotor side converter (504) and stator (503) of the DFIG (301) is connected directly to the grid (414). The stator (503) generates the fixed AC source fed directly to grid (414). Whereas the rotor (502) at the super synchronous speed feed AC to rotor side converter (504) and convert to DC. At sub synchronous speed the rotor side converter (504) convert DC to variable AC and feed to rotor (502). The DC link capacitor (408) is connected parallel between the rotor side converter (504) and the grid side inverter (505). The grid side inverter (505) configuration in the wind power generation system (500) is in the same manner as that of the inverter (409) as explained in Figure 4. At super synchronous speed, the DC from the power source (401) is converted to a fixed AC by the grid side converter (505), which is fed to the grid (414). Figure 6 illustrates a solar application system in accordance with the present disclosure. As shown in the Figure 6, the solar power generation system (600) consists of a power source (401), a DC link capacitor (408) and an inverter (409) connected to a grid (414) via a transformer (412) and a filter (43). Further, the power source (401) consists of photo voltaic cells (601) and a DC to DC converter (602) to converts solar energy to electrical energy which is in form of a DC. The DC link capacitor is connected parallel between the power source (401) and the inverter (409). The inverter (409) as illustrated in Figure 4 is configured in the solar power generation system (600). The DC from the power source (401) is converted to a fixed AC by the inverter (609) which is fed to the grid (414) via the transformer (412) and the filter (413). In one embodiment, the upper switches and the lower switches of the first inverter (410) and the second inverter (411) are operated in one of the phases (a-phase, b- phase and c-phase), and a DC bus voltage (Vdc) may appear across the primary winding of the transformer (412) of the predefine phase which is phase voltage for that corresponding phase. For example, when operating at a-phase, if the upper switch of the a-phase arm of the first inverter (410) is ON and the lower switch of the a-phase arm of the second inverter (411) is ON, then the complete Vdc will appear as the a-phase voltage across the primary winding of the transformer which connects the a-phase arms of the inverters. Similarly, if the lower switch of a-phase arm of the first inverter (410) is ON and the upper switch of the a-phase arm of the second inverter (411) is ON, then the DC bus voltage in opposite direction (-Vdc) will appear as the a-phase voltage across the corresponding primary winding of the transformer (412) which connects the a-phase arms of the inverters. With this defined operations of the switches, the complete Vdc may appear as the phase voltage across the primary windings unlike in conventional topology of the inverter. The inverter (409), which directly controls operation of the switches of the arms of the inverters (410 and 411), improves the DC bus utilization as the complete Vdc will appear as the phase voltage. Even though the complete Vdc appears as the phase voltage across the windings with selection of switching pattern, since the inverters (410 and 411) are connected to common DC link, a strong circulating current flows through the transformer (412). In order to eliminate circulating current, Zero Sequence Voltages (ZSV) has to be eliminated which is performed using a pulse width modulation (PWM) technique. This PWM technique may completely eliminate the ZSV in the inverter (409). The PWM technique is to completely suppress the circulating current and at same time to maintain the Vdc across the windings of the transformer (412). One embodiment of the present disclosure is using PWM technique. The suppression of the circulating currents provides flexibility to connect the first inventor and the second inverter to common DC bus as shown in Figure 4. Phase connected arms are denoted as aa’ (for a-phase), bb’ (for b-phase) and cc’ (for c phase). In each arm, the upper switch is in complementary with the lower switch that is, if the upper switch is ON then the lower switch is OFF and vice versa. Using each arm, two switching states may be exhibited. Therefore, the six arms (a, b, c, a’, b’ and c’) in the circuit can exhibit 26 i.e. 64 switching states. The ZSV for this circuit is calculated using the equation: V_ZSV=(V_dc [(S_a-S_(a^' ) )+(S_b-S_(b^' ) )+(S_c-S_(c^' ) )])/6………….. (3) Here, Sa, Sb and Sc represent switching states of the upper switches of the first inverter (410) and Sa’, Sb’ and Sc’ represent switching states of the upper switches of the second inverter (411) as shown in Figure 4. The switching states are one of 1 (ON) and 0 (OFF). The ZSV for all switching combinations are calculated using the equation 3 is tabulated in Table-2. Table-2 Table 2 shows the phase vector space vector for all the 64 switching states of the new topology. As shown in the Table 1, 1 to 8 (first column) columns represents the switching combinations of the first inverter and 1’to 8’ (first row) represents the switching combinations of the second inverter. The resulting common mode voltage is shown in Table 2 for the corresponding switching combinations. From Table 2, it is clear that some switching combinations of the first inverter and the second inverter results in ZSVs. Hence, the switching combinations which are 11’, 13’, 15’, 22’, 24’, 26’, 31’, 33’, 35’, 42’, 44’, 46’, 51’, 53’, 55’, 62’, 64’, and 66’ are used to nullify ZSVs completely. For the above switching combinations which are used to nullify ZSV, the phase voltage vector is calculated using: V_ref=V_dc [(S_a-S_(a^' ) )+(S_b-S_(b^' ) ) e^(j2p/s)+(S_c-S_(c^' ) ) e^(j4p/s) ]………. (4) and corresponding phase voltage vectors are tabulated in Table 3. Table 3 Table 3 shows the phase voltage vector for switching combinations which give ZSV. The magnitudes of the phase voltages for the null zero-sequence combinations are either (v3)/2 or 0 as shown in Table 3, which indicates that the phase voltage varies between (v3)/2 and 0 and maximum of the phase voltage that can be derived using these switching state is (v3)/2 i.e. 0.866 whereas in the conventional topology as shown in Figure 1, maximum magnitude of the phase voltage is 2/3 i.e. 0.666 which is illustrated in Table 1. Figure 7 illustrates a plot representing the space vector representation of the PWM, in accordance with the present disclosure; The Figure 7 shows the difference between convention PWM (702) and conventional Sine triangle PWM (703) with proposed PWM (701). In PWM with the conventional topology as in Figure 1, it is possible to obtain the maximum DC bus utilization of 0.66 whereas with the inverter (409) as shown in Figure 4 using with the proposed PWM the DC bus utilization is 0.866. The inverter (409) as shown in Figure 4 is better than the conventional systems as shown in Figure 1 with respect to the DC bus utilization which is illustrated in Figure 7. Further, this indicates that for a given Vdc, the phase voltage derived using the inventor (409) of Figure 4 is 20% more than the conventional topology of the inverter (109) of Figure 1. The inverter (409) as shown in Figure 4 with nullified zero voltage PWM will have provision to vary modulation index in order to get constant frequency and constant magnitudes even when the DC bus voltages are varying from minimum values to maximum values. Whereas for the inverter as (409) illustrated in Figure 4, minimum DC bus voltage operating range is 24% lesser than that of the conventional inverter (109) as in Figure 1, 2 and 3. But maximum operational DC bus voltage remains same for the both conventional inverter (109) and the proposed inverter (409) configurations. This indicates that overall system operating range to feed energy to grid (414) from the power source (401) is increased significantly. The inverter as shown in Figure 4 with nullified zero sequence voltage PWM technique is simulated in MATLAB/Simulink. In this simulation, both conventional and proposed systems are made to operate at 50 Hz and the phase voltage of the converter is observed with varying DC bus voltage and modulation index. As explained, the phase voltage magnitude depends upon the DC bus voltage and the modulation index. For all modulation indices and DC bus voltages, the frequency of the phase voltage is maintained at 50 Hz and corresponding magnitude is varied with respect to change in the modulation index and DC bus voltages. Embodiments of the present disclosure provide the advantages such as achieving DC bus utilization, i.e. 24% more when compare to the conventional systems. The inverter (609) for DC bus utilization not only improves the operating range of the DFIG at lower values of Vdc but also improve a Low Voltage Ride Through (LVRT) capability during fault conditions by injecting more reactive power. Also the circulating current in the inverter is supressed as explained, wherein the switches in the first inverter may be functional. However, the switches in the second inverter may be controlled according with the proposed algorithm in the instant disclosure to suppress the circulating current while supplying the fixed AC to the grid. Similarly, the second inverter may be functional and the circulating current is supressed by controlling the switches in the first inverter. Further, the inverter of the instant disclosure implemented in one or more embodiments which help in enhancing the DC bus utilization is not limited to the instant embodiments disclosed. However a person skilled in art can envisage other application in the area of power electronics in which the current disclosure can be used. Further, the instant disclosure can be readily adopted in similar application with minor modification without departing from the scope of the present disclosure. The terms "an embodiment", "embodiment", "embodiments", "the embodiment", "the embodiments", "one or more embodiments", "some embodiments", and "one embodiment" mean "one or more (but not all) embodiments of the invention(s)" unless expressly specified otherwise. The terms "including", "comprising", “having” and variations thereof mean "including but not limited to", unless expressly specified otherwise. The terms "a", "an" and "the" mean "one or more", unless expressly specified otherwise. When a single device or article is described herein, it will be readily apparent that more than one device/article (whether or not they cooperate) may be used in place of a single device/article. Similarly, where more than one device or article is described herein (whether or not they cooperate), it will be readily apparent that a single device/article may be used in place of the more than one device or article or a different number of devices/articles may be used instead of the shown number of devices or programs. The functionality and/or the features of a device may be alternatively embodied by one or more other devices which are not explicitly described as having such functionality/features. Thus, other embodiments of the invention need not include the device itself. The foregoing description of various embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto. The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended. Finally, the language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based here on. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims. With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group. While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims. Referral Numerals: Reference Number Description 100 conventional wind power generation system with a generator 101,401 power source 102,402 wind turbine 103,403 gear box 104,404 generator 105,405 rotor of the generator 106,406 stator of the generator 107 AC to DC converter 108,408 DC link capacitor 109 conventional inverter 110 transformer and filter 111,414 grid 200 conventional wind power generation system with doubly fed induction generator (DFIG) 201,501 DFIG 202,502 rotor of the DFIG 203,503 stator of the DFIG 204,504 rotor side converter 205,505 grid side converter 300 conventional solar power generation system with a generator 301,601 photo voltaic cells 302,602 DC to DC converter 400 proposed wind power generation system with generator 407 converter 409 proposed inverter 410 first inverter 411 second inverter 412 transformer 413 filter 500 proposed wind power generation system with DFIG 600 proposed solar power generation system 700 space vector diagram of proposed pulse width modulation (PWM) technique 701 proposed PWM 702 conventional PWM 703 conventional sine triangle PWM : An inverter used for Direct Current (DC) bus utilization, comprising: a first inverter and a second inverter, electrically coupled back to back through primary winding of an electric transformer and a DC link capacitor connected to a power source in parallel with the inverter for adjusting waveform of signal output through the power source, wherein the inverter is electrically coupled to a grid through secondary winding of the electric transformer. The inverter as claimed in claim 1, wherein arms of same phase of the first inverter and the second inverter are connected to each ends of the primary winding of the electric transformer. A system used for Direct Current (DC) bus utilization, comprising: a power source to provide a DC; and an inverter comprising, a first inverter and a second inverter, electrically coupled back to back through primary winding of an electric transformer and a DC link capacitor connected to the power source in parallel with the inverter for adjusting waveform of signal output through the power source, wherein the inverter is electrically coupled to a grid through secondary winding of the electric transformer. The system as claimed in claim 3, wherein the power source is a wind turbine with a Doubly Fed Induction Generator (DFIG) coupled to a converter to provide the DC. The system as claimed in claim 4, wherein a rotor of the DFIG is electrically connected to the converter and a stator of the DFIG is electrically connected to a grid. The system as claimed in claim 3, wherein the power source is a wind turbine coupled with an asynchronous machine and electrically connected to a converter to provide the DC. The system as claimed in claim 3, wherein the power source is a wind turbine coupled with a synchronous machine and electrically connected to a converter to provide the DC. The system as claimed in claim 3, wherein the power source is solar photo voltaic electrically coupled to a converter to provide the DC. A wind power generation system, comprising the system used for DC bus utilization according to claim 3. A solar power generation system, comprising the system used for DC bus utilization according to claim 3. A method for Direct Current (DC) bus utilization, comprising acts of: providing a DC from a power source; converting the DC to a fixed AC by an inverter comprising, a first inverter and a second inverter, electrically coupled back to back through a primary winding of an electric transformer; and supplying the fixed AC to a grid, electrically coupled to a secondary winding of the electric transformer. The method as claimed in claim 9, wherein the inverter comprises of switches whose operation can be controlled in at least one of the first inverter and the second inverter to suppress a circulating current while supplying the fixed AC to the grid. The method as claimed in claim 10, wherein the operation of the switches in the first inverter is controlled to supress the circulating current by maintaining a predefined position of the switches in the second inverter. A method for wind power generation system, comprising the method for DC bus utilization according to claim 9. A method for solar power generation system, comprising the method for DC bus utilization according to claim 9. Dated: this 26th day of February, 2015 NAVEEN SURIYA IN/PA – 1419 Of K&S PARTNERS AGENT FOR THE APPLICANT AN INVERTER FOR DIRECT CURRENT (DC) BUS UTILIZATION AND A METHOD THEREOF ABSTRACT Embodiments of the present disclosure relates to an inverter for Direct Current (DC) bus utilization comprising of a first inverter and a second inverter which are electrically coupled back to back through primary winding of an electric transformer and a DC link capacitor connected to a power source in parallel with the inverter for adjusting waveform of signal output through the power source. The inverter is electrically coupled to a grid through secondary winding of the electric transformer. Also, the present disclosure proposes a system and a method used for Direct Current (DC) bus utilization, comprising of a power source to provide a DC to the inverter. The DC is converted to a fixed AC by the inverter and supplies the fixed AC to the grid. Figures 4

CLIAMS:We claim:
1. An inverter used for Direct Current (DC) bus utilization, comprising:
a first inverter and a second inverter, electrically coupled back to back through primary winding of an electric transformer and a DC link capacitor connected to a power source in parallel with the inverter for adjusting waveform of signal output through the power source, wherein the inverter is electrically coupled to a grid through secondary winding of the electric transformer.

2. The inverter as claimed in claim 1, wherein arms of same phase of the first inverter and the second inverter are connected to each ends of the primary winding of the electric transformer.

3. A system used for Direct Current (DC) bus utilization, comprising:
a power source to provide a DC; and
an inverter comprising, a first inverter and a second inverter, electrically coupled back to back through primary winding of an electric transformer and a DC link capacitor connected to the power source in parallel with the inverter for adjusting waveform of signal output through the power source, wherein the inverter is electrically coupled to a grid through secondary winding of the electric transformer.

4. The system as claimed in claim 3, wherein the power source is a wind turbine with a Doubly Fed Induction Generator (DFIG) coupled to a converter to provide the DC.

5. The system as claimed in claim 4, wherein a rotor of the DFIG is electrically connected to the converter and a stator of the DFIG is electrically connected to a grid.

6. The system as claimed in claim 3, wherein the power source is a wind turbine coupled with an asynchronous machine and electrically connected to a converter to provide the DC.

7. The system as claimed in claim 3, wherein the power source is a wind turbine coupled with a synchronous machine and electrically connected to a converter to provide the DC.

8. The system as claimed in claim 3, wherein the power source is solar photo voltaic electrically coupled to a converter to provide the DC.
9. A wind power generation system, comprising the system used for DC bus utilization according to claim 3.

10. A solar power generation system, comprising the system used for DC bus utilization according to claim 3.

11. A method for Direct Current (DC) bus utilization, comprising acts of:
providing a DC from a power source;
converting the DC to a fixed AC by an inverter comprising, a first inverter and a second inverter, electrically coupled back to back through a primary winding of an electric transformer; and
supplying the fixed AC to a grid, electrically coupled to a secondary winding of the electric transformer.

12. The method as claimed in claim 9, wherein the inverter comprises of switches whose operation can be controlled in at least one of the first inverter and the second inverter to suppress a circulating current while supplying the fixed AC to the grid.

13. The method as claimed in claim 10, wherein the operation of the switches in the first inverter is controlled to supress the circulating current by maintaining a predefined position of the switches in the second inverter.

14. A method for wind power generation system, comprising the method for DC bus utilization according to claim 9.

15. A method for solar power generation system, comprising the method for DC bus utilization according to claim 9.
,TagSPECI:TECHNICAL FIELD
The present disclosure generally relates to an area of power electronics. The disclosure discloses embodiments of a device, system and method for an improved Direct Current (DC) bus utilization.

BACKGROUND
Presently, a renewable power generation system consists of a power source including a converter which converts variable frequency into DC, a DC link capacitor, an inverter electrically coupled to a grid via a transformer. The inverter, electrically coupled with the grid, converts the DC which is provided by the power source to a fixed alternate current (AC). The DC link capacitor is electrically coupled in parallel between the power source and the inverter. The inverter along with the DC link capacitor provides a real power and a reactive power according to the demands of the grid. Control of the reactive power of the inverter is more crucial in order to balance a voltage stability of the power generation system. Also, the power generation system should be in synchronization with the grid during fault condition according to a defined requirement of a low voltage ride through (LVRT) grid code standard. However for a given DC bus voltage; there exist a limitation in the existing power generation system because of constraints with respect to topology of the inverter and variations in the power source.

Figure 1 shows an exemplary prior art embodiment of a wind power generation system (100). The system (100) consists of a power source (101), a DC link capacitor (108) and an inverter (109) which is electrically coupled with a grid (111) via an electric transformer and a filter (110). Further, the power source (101) consists of a wind turbine (102), a gear box (103), a generator (104) and an AC to DC converter (107). The generator (104) is a synchronous machine or an asynchronous machine and only stator (106) of the generator (104) is connected to the converter (107). Further, the wind turbine (101), the gear box (102) and the generator (103) are mechanically coupled and convert wind energy to electrical energy which is in form of a variable AC which is further converted to DC by the converter (107). . Further, the inverter in the system (100) converts the DC into a fixed AC and feds to the grid.

Figure 2 shows another exemplary prior art embodiment of a wind power generation system (200). The system (200) consists of a power source (101), a DC link capacitor (108) and a grid side converter (205) which is electrically coupled with a grid (111) via an electric transformer and a filter (110). Further, the power source (101) consists of a wind turbine (102), a gear box (103), a doubly fed induction generator (DFIG) (201) and a rotor side converter (204). The wind turbine (102), the gear box (103) and the DFIG (201) are mechanically coupled and convert wind energy to electrical energy which is in form of a variable AC. A rotor (202) of the DFIG (201) is connected to the rotor side converter (204) wherein a stator (203) of the DFIG is connected to the grid (111) directly. Further as illustrated with respect to Figure 1, at super synchronous speed the variable AC is converted to DC by the rotor side converter (204) and the DC is converted to a fixed AC by the grid side converter which is fed to the grid (111). But at sub synchronous speed the fixed AC is converted to DC by the grid side converter (205) and the DC is converted to a variable AC by the rotor side converter (204).

Further, Figure 3 shows an exemplary prior art embodiment of a solar power generation system (300). The system (300) consists of a power source (101), a DC link capacitor (108) and an inverter (109) which is electrically coupled with a grid (111) via an electric transformer and a filter (110). Further, the power source (101) consists of photo voltaic cells (301) and a DC to DC converter (302). The photo voltaic cells (301) together with the DC to DC converter that is the power source (101) convert solar energy to electrical energy which is in form of a DC. The inverter (109) converts the DC to a fixed AC which is further fed to the grid (111).

However, in order to feed a power into the grid (111) by the inverter (109) as illustrated in the exemplary embodiments in Figure 1, Figure 2 and Figure 3, the inverter (109) must always be maintained at a fixed frequency of 50 Hz and at a defined grid voltage. But voltages from the power source (101) is of variable frequencies which depends upon wind speed in the wind power generation system and depends on voltage drop across the photo voltaic cells in the solar power generation system. Therefore, in order to get the fixed frequency of 50 Hz and required voltages at the inverter (109), voltages with variable frequencies from the power source (101) are converted to DC using converters and then to fixed AC by the inverter (109). In this conventional process of converting the variable AC to DC and DC to a fixed AC, DC bus voltage (Vdc) has to be maintained at a defined value to feed energy into grid (111) with improved power quality. The available DC link capacitor (107) voltage mainly depends upon the availability of the power at power source and power source configuration. Whereas the maintenance is tough when the DC bus voltage is lesser than the defined value and thereby the power fed to the grid will be affected which is a limitation with regard to conventional systems.

Further, for the existing inverter (109) implemented in any power generation system, the maximum of phase voltage occurs in the inverter that is the DC bus utilization happens only for 2/3 (Vdc) and also zero sequence voltage (ZSV) occurs only for a single switching state of the inverter (109). Further to this, there arises circulating current in the inverter of the system which is impractical to suppress with the existing inverter (109) switching which is another limitation of the conventional systems.

Accordingly, a need exists for a system to improve the DC bus utilization and to overcome one or more limitations stated above.

SUMMARY
One or more shortcomings of the prior art are overcome and additional advantages are provided through the present disclosure. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.

The present disclosure proposes a new topology for an inverter for DC bus utilization. The inverter comprises of a first inverter and a second inverter which are electrically coupled back to back through primary winding of an electric transformer and a DC link capacitor is connected to a power source in parallel with the inverter for adjusting waveform of signal output through the power source. The inverter is electrically coupled to a grid through secondary winding of the electric transformer. Further, the present disclosure proposes a system for DC bus utilization, comprising of a power source to provide a DC to the proposed new topology of the inverter. The DC is converted to a fixed AC by the inverter and supplies the fixed AC to the grid. Also, the present disclosure proposes a method in the system used for DC bus utilization, which involves in providing the DC by the power source to the inverter through a DC link capacitor. The inverter converts the DC to fixed AC and feeds it the grid through the electric transformer.

The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects and features described above, further aspects, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate exemplary embodiments and, together with the description, serve to explain the disclosed principles. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system and/or methods in accordance with embodiments of the present subject matter are now described, by way of example only, and with reference to the accompanying figures, in which:

Figure 1 illustrates an embodiment of a conventional wind power generation system;

Figure 2 illustrates another embodiment of a conventional wind power generation system;

Figure 3 illustrates an embodiment of a conventional solar power generation system;

Figure 4 illustrates an exemplary embodiment of a wind application with a synchronous machine in accordance with the present disclosure;

Figure 5 illustrates an exemplary embodiment of a wind application with a doubly fed induction generator (DFIG) in accordance with the present disclosure;

Figure 6 illustrates an exemplary embodiment of a solar application in accordance with the present disclosure;

Figure 7 illustrates a plot representing a space vector representation of PWM, in accordance with the present disclosure;

It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative systems embodying the principles of the present subject matter. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and executed by a computer or processor, whether or not such computer or processor is explicitly shown.

DETAILED DESCRIPTION
The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the claims of the disclosure. It should be appreciated by those skilled in the art that the conception and specific aspect disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure.

In the present document, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the disclosure.

The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a system or apparatus proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or apparatus.

Embodiments of the present disclosure relates to a new topology of an inverter used for DC bus utilization. The inverter comprises of a first inverter and a second inverter which are electrically coupled back to back through primary winding of an electric transformer and a DC link capacitor connected to a power source in parallel with the inverter for adjusting waveform of signal output through the power source. Further, the inverter is electrically coupled to a grid through secondary winding of the electric transformer. Also, the present disclosure relates to a system used for DC bus utilization which consists of a power source to provide a DC, said new topology of the inventor and a DC link capacitor connected to the power source in parallel with the inverter. Also, the present disclosure relates to a method for DC bus utilization which involves in providing a DC from a power source to the inverter which converts the DC to a fixed AC and supplying the fixed AC to a grid, electrically coupled to a secondary winding of the electric transformer.

In the following detailed description of the embodiments of the disclosure, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, not to be taken in a limiting sense.

Figure 4 illustrates an exemplary embodiment of a wind application with a generator in accordance with the present disclosure.

As shown in Figure 4, the wind power generation system (400) converts wind energy to an electrical energy. The wind power generation system (400) consists of a power source (401), a DC link capacitor (408) and an inverter (409). The inverter (409) has a modified topology with respect to an inverter existing in any conventional systems. Further, the power source (401) consists of a wind turbine (402), a gear box (403), a generator (404) and a converter (407). The generator in the system (400) may be a synchronous machine. Stator (406) of the generator (404) is connected to the converter (407). Further, the DC link capacitor (408) is connected in parallel between the converter (407) and the inverter (409) in the power generation system (400). The inverter unit (409) consist of two inverters, a first inverter (410) and a second inverter (411), connected via a transformer (412). In the power generation system (400), configuration of the first inverter with a–phase, b-phase and c-phase arms is represented with a, b and c respectively and corresponding switching states represented as Sa, Sb and Sc respectively. Similarly, configuration of the second inverter with a-phase, b-phase and c-phase arms is represented with a’, b’ and c’ respectively and corresponding switching states are represented with Sa’, Sb’ and Sc’ respectively. An upper switch and a lower switch of each arm (a, b, c, a’, b’ and c’) of the inverter, are complementary to each other. Each side of primary winding of the transformer (611) is connected to each arm of the inverter of same phase and the secondary winding of the transformer (611) is connected to the grid (614) via a filter (413). The filter (413) is used to process the waveform and separate the unwanted frequencies from the desired waveform. This connection between the inverter (409) and the grid (414) via the transformer (412) and the filter (413) is illustrated in Figure 4. Further, the power source provides electrical energy in the form of a DC. The inverter (409) converts the DC which is one of a fixed DC or a variable DC into a fixed AC and is fed to the grid (414) via a filter (413).

Figure 5 illustrates a wind application system with a doubly fed induction generator (DFIG) in accordance with one embodiment of the present disclosure.

As shown in Figure 5, the wind power generation system (500) comprises a power source (401), a DC link capacitor (408) and a grid side converter (505) connected to a grid (414) via a filter (413). Further, the power source (401) consists of a wind turbine (402), electrically coupled with a DFIG (501) and a rotor side converter (504). Further, rotor (502) of the DFIG (501) is connected to the rotor side converter (504) and stator (503) of the DFIG (301) is connected directly to the grid (414). The stator (503) generates the fixed AC source fed directly to grid (414). Whereas the rotor (502) at the super synchronous speed feed AC to rotor side converter (504) and convert to DC. At sub synchronous speed the rotor side converter (504) convert DC to variable AC and feed to rotor (502).

The DC link capacitor (408) is connected parallel between the rotor side converter (504) and the grid side inverter (505). The grid side inverter (505) configuration in the wind power generation system (500) is in the same manner as that of the inverter (409) as explained in Figure 4. At super synchronous speed, the DC from the power source (401) is converted to a fixed AC by the grid side converter (505), which is fed to the grid (414).

Figure 6 illustrates a solar application system in accordance with the present disclosure.

As shown in the Figure 6, the solar power generation system (600) consists of a power source (401), a DC link capacitor (408) and an inverter (409) connected to a grid (414) via a transformer (412) and a filter (43). Further, the power source (401) consists of photo voltaic cells (601) and a DC to DC converter (602) to converts solar energy to electrical energy which is in form of a DC. The DC link capacitor is connected parallel between the power source (401) and the inverter (409). The inverter (409) as illustrated in Figure 4 is configured in the solar power generation system (600). The DC from the power source (401) is converted to a fixed AC by the inverter (609) which is fed to the grid (414) via the transformer (412) and the filter (413).

In one embodiment, the upper switches and the lower switches of the first inverter (410) and the second inverter (411) are operated in one of the phases (a-phase, b- phase and c-phase), and a DC bus voltage (Vdc) may appear across the primary winding of the transformer (412) of the predefine phase which is phase voltage for that corresponding phase. For example, when operating at a-phase, if the upper switch of the a-phase arm of the first inverter (410) is ON and the lower switch of the a-phase arm of the second inverter (411) is ON, then the complete Vdc will appear as the a-phase voltage across the primary winding of the transformer which connects the a-phase arms of the inverters. Similarly, if the lower switch of a-phase arm of the first inverter (410) is ON and the upper switch of the a-phase arm of the second inverter (411) is ON, then the DC bus voltage in opposite direction (-Vdc) will appear as the a-phase voltage across the corresponding primary winding of the transformer (412) which connects the a-phase arms of the inverters. With this defined operations of the switches, the complete Vdc may appear as the phase voltage across the primary windings unlike in conventional topology of the inverter. The inverter (409), which directly controls operation of the switches of the arms of the inverters (410 and 411), improves the DC bus utilization as the complete Vdc will appear as the phase voltage.

Even though the complete Vdc appears as the phase voltage across the windings with selection of switching pattern, since the inverters (410 and 411) are connected to common DC link, a strong circulating current flows through the transformer (412). In order to eliminate circulating current, Zero Sequence Voltages (ZSV) has to be eliminated which is performed using a pulse width modulation (PWM) technique. This PWM technique may completely eliminate the ZSV in the inverter (409). The PWM technique is to completely suppress the circulating current and at same time to maintain the Vdc across the windings of the transformer (412).

One embodiment of the present disclosure is using PWM technique. The suppression of the circulating currents provides flexibility to connect the first inventor and the second inverter to common DC bus as shown in Figure 4. Phase connected arms are denoted as aa’ (for a-phase), bb’ (for b-phase) and cc’ (for c phase). In each arm, the upper switch is in complementary with the lower switch that is, if the upper switch is ON then the lower switch is OFF and vice versa. Using each arm, two switching states may be exhibited. Therefore, the six arms (a, b, c, a’, b’ and c’) in the circuit can exhibit 26 i.e. 64 switching states. The ZSV for this circuit is calculated using the equation:

V_ZSV=(V_dc [(S_a-S_(a^' ) )+(S_b-S_(b^' ) )+(S_c-S_(c^' ) )])/6………….. (3)

Here, Sa, Sb and Sc represent switching states of the upper switches of the first inverter (410) and Sa’, Sb’ and Sc’ represent switching states of the upper switches of the second inverter (411) as shown in Figure 4. The switching states are one of 1 (ON) and 0 (OFF).

The ZSV for all switching combinations are calculated using the equation 3 is tabulated in Table-2.

Table-2

Table 2 shows the phase vector space vector for all the 64 switching states of the new topology.

As shown in the Table 1, 1 to 8 (first column) columns represents the switching combinations of the first inverter and 1’to 8’ (first row) represents the switching combinations of the second inverter. The resulting common mode voltage is shown in Table 2 for the corresponding switching combinations. From Table 2, it is clear that some switching combinations of the first inverter and the second inverter results in ZSVs. Hence, the switching combinations which are 11’, 13’, 15’, 22’, 24’, 26’, 31’, 33’, 35’, 42’, 44’, 46’, 51’, 53’, 55’, 62’, 64’, and 66’ are used to nullify ZSVs completely.

For the above switching combinations which are used to nullify ZSV, the phase voltage vector is calculated using:

V_ref=V_dc [(S_a-S_(a^' ) )+(S_b-S_(b^' ) ) e^(j2p/s)+(S_c-S_(c^' ) ) e^(j4p/s) ]………. (4)

and corresponding phase voltage vectors are tabulated in Table 3.

Table 3


Table 3 shows the phase voltage vector for switching combinations which give ZSV. The magnitudes of the phase voltages for the null zero-sequence combinations are either (v3)/2 or 0 as shown in Table 3, which indicates that the phase voltage varies between (v3)/2 and 0 and maximum of the phase voltage that can be derived using these switching state is (v3)/2 i.e. 0.866 whereas in the conventional topology as shown in Figure 1, maximum magnitude of the phase voltage is 2/3 i.e. 0.666 which is illustrated in Table 1.

Figure 7 illustrates a plot representing the space vector representation of the PWM, in accordance with the present disclosure;

The Figure 7 shows the difference between convention PWM (702) and conventional Sine triangle PWM (703) with proposed PWM (701). In PWM with the conventional topology as in Figure 1, it is possible to obtain the maximum DC bus utilization of 0.66 whereas with the inverter (409) as shown in Figure 4 using with the proposed PWM the DC bus utilization is 0.866. The inverter (409) as shown in Figure 4 is better than the conventional systems as shown in Figure 1 with respect to the DC bus utilization which is illustrated in Figure 7. Further, this indicates that for a given Vdc, the phase voltage derived using the inventor (409) of Figure 4 is 20% more than the conventional topology of the inverter (109) of Figure 1.

The inverter (409) as shown in Figure 4 with nullified zero voltage PWM will have provision to vary modulation index in order to get constant frequency and constant magnitudes even when the DC bus voltages are varying from minimum values to maximum values. Whereas for the inverter as (409) illustrated in Figure 4, minimum DC bus voltage operating range is 24% lesser than that of the conventional inverter (109) as in Figure 1, 2 and 3. But maximum operational DC bus voltage remains same for the both conventional inverter (109) and the proposed inverter (409) configurations. This indicates that overall system operating range to feed energy to grid (414) from the power source (401) is increased significantly.

The inverter as shown in Figure 4 with nullified zero sequence voltage PWM technique is simulated in MATLAB/Simulink. In this simulation, both conventional and proposed systems are made to operate at 50 Hz and the phase voltage of the converter is observed with varying DC bus voltage and modulation index. As explained, the phase voltage magnitude depends upon the DC bus voltage and the modulation index. For all modulation indices and DC bus voltages, the frequency of the phase voltage is maintained at 50 Hz and corresponding magnitude is varied with respect to change in the modulation index and DC bus voltages.

Embodiments of the present disclosure provide the advantages such as achieving DC bus utilization, i.e. 24% more when compare to the conventional systems. The inverter (609) for DC bus utilization not only improves the operating range of the DFIG at lower values of Vdc but also improve a Low Voltage Ride Through (LVRT) capability during fault conditions by injecting more reactive power. Also the circulating current in the inverter is supressed as explained, wherein the switches in the first inverter may be functional. However, the switches in the second inverter may be controlled according with the proposed algorithm in the instant disclosure to suppress the circulating current while supplying the fixed AC to the grid. Similarly, the second inverter may be functional and the circulating current is supressed by controlling the switches in the first inverter. Further, the inverter of the instant disclosure implemented in one or more embodiments which help in enhancing the DC bus utilization is not limited to the instant embodiments disclosed. However a person skilled in art can envisage other application in the area of power electronics in which the current disclosure can be used. Further, the instant disclosure can be readily adopted in similar application with minor modification without departing from the scope of the present disclosure.

The terms "an embodiment", "embodiment", "embodiments", "the embodiment", "the embodiments", "one or more embodiments", "some embodiments", and "one embodiment" mean "one or more (but not all) embodiments of the invention(s)" unless expressly specified otherwise.

The terms "including", "comprising", “having” and variations thereof mean "including but not limited to", unless expressly specified otherwise.

The terms "a", "an" and "the" mean "one or more", unless expressly specified otherwise.

When a single device or article is described herein, it will be readily apparent that more than one device/article (whether or not they cooperate) may be used in place of a single device/article. Similarly, where more than one device or article is described herein (whether or not they cooperate), it will be readily apparent that a single device/article may be used in place of the more than one device or article or a different number of devices/articles may be used instead of the shown number of devices or programs. The functionality and/or the features of a device may be alternatively embodied by one or more other devices which are not explicitly described as having such functionality/features. Thus, other embodiments of the invention need not include the device itself.

The foregoing description of various embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto. The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.

Finally, the language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based here on. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Referral Numerals:

Reference Number Description
100 conventional wind power generation system with a generator
101,401 power source
102,402 wind turbine
103,403 gear box
104,404 generator
105,405 rotor of the generator
106,406 stator of the generator
107 AC to DC converter
108,408 DC link capacitor
109 conventional inverter
110 transformer and filter
111,414 grid
200 conventional wind power generation system with doubly fed induction generator (DFIG)
201,501 DFIG
202,502 rotor of the DFIG
203,503 stator of the DFIG
204,504 rotor side converter
205,505 grid side converter
300 conventional solar power generation system with a generator
301,601 photo voltaic cells
302,602 DC to DC converter
400 proposed wind power generation system with generator
407 converter
409 proposed inverter
410 first inverter
411 second inverter
412 transformer
413 filter
500 proposed wind power generation system with DFIG
600 proposed solar power generation system
700 space vector diagram of proposed pulse width modulation (PWM) technique
701 proposed PWM
702 conventional PWM
703 conventional sine triangle PWM

We claim:
An inverter used for Direct Current (DC) bus utilization, comprising:
a first inverter and a second inverter, electrically coupled back to back through primary winding of an electric transformer and a DC link capacitor connected to a power source in parallel with the inverter for adjusting waveform of signal output through the power source, wherein the inverter is electrically coupled to a grid through secondary winding of the electric transformer.

The inverter as claimed in claim 1, wherein arms of same phase of the first inverter and the second inverter are connected to each ends of the primary winding of the electric transformer.

A system used for Direct Current (DC) bus utilization, comprising:
a power source to provide a DC; and
an inverter comprising, a first inverter and a second inverter, electrically coupled back to back through primary winding of an electric transformer and a DC link capacitor connected to the power source in parallel with the inverter for adjusting waveform of signal output through the power source, wherein the inverter is electrically coupled to a grid through secondary winding of the electric transformer.

The system as claimed in claim 3, wherein the power source is a wind turbine with a Doubly Fed Induction Generator (DFIG) coupled to a converter to provide the DC.

The system as claimed in claim 4, wherein a rotor of the DFIG is electrically connected to the converter and a stator of the DFIG is electrically connected to a grid.

The system as claimed in claim 3, wherein the power source is a wind turbine coupled with an asynchronous machine and electrically connected to a converter to provide the DC.

The system as claimed in claim 3, wherein the power source is a wind turbine coupled with a synchronous machine and electrically connected to a converter to provide the DC.

The system as claimed in claim 3, wherein the power source is solar photo voltaic electrically coupled to a converter to provide the DC.
A wind power generation system, comprising the system used for DC bus utilization according to claim 3.

A solar power generation system, comprising the system used for DC bus utilization according to claim 3.

A method for Direct Current (DC) bus utilization, comprising acts of:
providing a DC from a power source;
converting the DC to a fixed AC by an inverter comprising, a first inverter and a second inverter, electrically coupled back to back through a primary winding of an electric transformer; and
supplying the fixed AC to a grid, electrically coupled to a secondary winding of the electric transformer.

The method as claimed in claim 9, wherein the inverter comprises of switches whose operation can be controlled in at least one of the first inverter and the second inverter to suppress a circulating current while supplying the fixed AC to the grid.

The method as claimed in claim 10, wherein the operation of the switches in the first inverter is controlled to supress the circulating current by maintaining a predefined position of the switches in the second inverter.

A method for wind power generation system, comprising the method for DC bus utilization according to claim 9.

A method for solar power generation system, comprising the method for DC bus utilization according to claim 9.

Dated: this 26th day of February, 2015
NAVEEN SURIYA
IN/PA – 1419
Of K&S PARTNERS
AGENT FOR THE APPLICANT

AN INVERTER FOR DIRECT CURRENT (DC) BUS UTILIZATION AND A METHOD THEREOF

ABSTRACT

Embodiments of the present disclosure relates to an inverter for Direct Current (DC) bus utilization comprising of a first inverter and a second inverter which are electrically coupled back to back through primary winding of an electric transformer and a DC link capacitor connected to a power source in parallel with the inverter for adjusting waveform of signal output through the power source. The inverter is electrically coupled to a grid through secondary winding of the electric transformer. Also, the present disclosure proposes a system and a method used for Direct Current (DC) bus utilization, comprising of a power source to provide a DC to the inverter. The DC is converted to a fixed AC by the inverter and supplies the fixed AC to the grid.

Figures 4