WO2017101951A1

WO2017101951A1 - Centralized power conversion system

Info

Publication number: WO2017101951A1
Application number: PCT/DK2016/050437
Authority: WO
Inventors: Anurag Gupta; Erik Carl Lehnskov Miranda; Jesper HILLEBRANDT; Philip Carne Kjaer; Torben Ladegaard Baun
Original assignee: Vestas Wind Systems A/S
Priority date: 2015-12-17
Filing date: 2016-12-16
Publication date: 2017-06-22

Abstract

Aspects of the present disclosure are generally directed to a multi-rotor turbine having with a common line-side converter (LSC) (DC to AC converter) for each of a plurality of machine-side converters (AC to DC converters). For example, the multi- rotor turbine may include a plurality of machine-side converters (MSC), each configured to receive an alternating current (AC) input signal from one of a plurality of rotors of the multi-rotor turbine and generate a DC signal based on the input AC signal. The multi-rotor turbine may also include a line-side converter (LSC) configured to receive the DC signals from each of the plurality of MSCs and generate an output AC signal based on the DC signals.

Description

CENTRALIZED POWER CONVERSION SYSTEM

BACKGROUND

Field of the Invention

Aspects of the present disclosure generally relate to techniques for conversion of power generated by a multi-rotor turbine.

Description of the Related Art

Modern power generation and distribution networks increasingly rely on renewable energy sources, such as wind turbine generators. In some cases, the wind turbine generators may be substituted for conventional, fossil fuel-based generators. Beyond merely generating and delivering electrical power, the wind turbine generators are responsible for contributing to grid stability through frequency regulation. Multi-rotor wind turbines provide several advantages over single rotor turbines, such as ease of installation, maintenance, and transportation.

SUMMARY Certain aspects of the present disclosure are generally directed to a multi- rotor turbine having with a common line-side converter (LSC) (DC to AC converter) for each of a plurality of machine-side converters (AC to DC converters). The multi- rotor turbine generally includes a plurality of machine-side converters (MSC), each configured to receive an input alternating current (AC) signal from one of a plurality of rotors of the multi-rotor turbine and generate a DC signal based on the input AC signal and a line-side converter (LSC) configured to receive the DC signals from each of the plurality of MSCs and generate an output AC signal based on the DC signals.

In general, each rotor may include an electrical generator. In general, each machine-side converter may be arranged to receive the input AC signal from the electrical generator of one of a plurality of rotors of the multi-rotor turbine.

Certain aspects of the present disclosure are directed to a power generation system. The power conversion system may generally include a plurality of multi-rotor turbines coupled to a power grid, wherein each multi-rotor turbine of the plurality of multi-rotor turbines comprises a plurality of machine-side converters (MSCs), each configured to receive an input alternating current (AC) signal from one of a plurality of rotors of a respective multi-rotor turbine of the plurality multi-rotor turbines and generate a DC signal based on the input AC signal and a line-side converter (LSC) configured to receive the DC signals from each of the plurality of MSCs and generate an AC output signal based on the DC signals and a transformer coupled to a power grid, and configured to adjust the voltage of the output AC signal and provide the voltage adjusted output AC signal to the power grid. Certain aspects of the present disclosure are directed to a method of assembly of a multi-rotor turbine. The method generally includes providing a plurality of machine-side converters (MSCs), each configured to receive an alternating current (AC) input signal from one of a plurality of rotors of a multi-rotor turbine and generate a DC signal based on the AC input signal and providing a line-side converter (LSC) configured to receive the DC signals from each of the plurality of MSCs and generate an output AC signal based on the DC signals and coupling outputs of the MSCs to the LSC.

BRIEF DESCRIPTION OF THE DRAWINGS So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only aspects of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective aspects.

FIG. 1 illustrates an example multi-rotor turbine.

FIG. 2 illustrates an example power conversion system of a multi-rotor turbine. FIG. 3 illustrates an example configuration of a power conversion system having a single line-side converter (LSC) for conversion of signals from multiple machine-side converters (MSCs), in accordance with certain aspects of the present disclosure. FIG. 4 illustrates the example configuration of FIG. 3 with the LSC located at a base of a tower of the multi-rotor turbine, in accordance with certain aspects of the present disclosure.

FIG. 5 illustrates the example configuration of FIG. 3 with the LSC located at a middle portion of a tower of the multi-rotor turbine, in accordance with certain aspects of the present disclosure.

FIG. 6 illustrates the example configuration of FIG. 3 with the MSCs located in a tower of the multi-rotor turbine, in accordance with certain aspects of the present disclosure.

FIG. 7 illustrates an example power conversion system having a DC chopper, in accordance with certain aspects of the present disclosure.

FIG. 8 illustrates example operations for assembly of a multi-rotor turbine, in accordance with certain aspects of the present disclosure.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one aspect of the present disclosure may be beneficially utilized on other aspects without specific recitation.

DETAILED DESCRIPTION

Aspects of present disclosure generally relate a centralized power conversion system for a multi-rotor wind turbine. For example, multiple rotors of a turbine may share a common line-side converter (LSC), otherwise referred to as a grid-side converter. The centralized power conversion system of the present disclosure provides advantages such as improved reliability, reduced load loss and reduced weight of nacelles. Moreover, the centralized power conversion system of the present disclosure does not compromise turbine operation for full scale converters. That is, although the centralized power conversion system includes a common LSC for multiple rotors, each rotor can still operate at different speeds, allowing each rotor to adjust its respective speed based on operating conditions.

FIG. 1 illustrates a wind turbine 100 with multiple rotors R-i , R₂, R₃, and R₄ (collectively rotors R_n). Each rotor is configured to transform kinetic energy of the wind into electrical energy. That is, the rotor blades are rotated about a shaft by the wind, which then powers electrical generators that may be located in nacelles 102A, 102B, 102C, 102D (collectively nacelles 102). The rotors are typically located on a tower 104 relatively high off the ground to ensure good airflow.

This electrical energy may be converted by a power conversion system to a form that can be fed into a power grid. Each rotor may have a designated power conversion system located in corresponding nacelles 102 of each of the rotors R_n. The weight of the rotors R_n and the nacelles 102, including the power conversion systems, are supported by the tower 104 and support bars 106A, 106B, 106C, and 106D (collectively support bars 106).

In general, each of the rotors R_n may include an electrical generator, which may be coupled to a power converter. Each electrical generator may be coupled to one or more transformers. The electrical generators are driven by the rotating shaft coupled to the blades of the rotors R_n to produce alternating current (AC) voltage which may vary in magnitude and frequency according to the wind speed. A gearbox may be used to step up the slow rotational speed of the shaft to a high rotational speed suitable for operating the electrical generator. The electrical generator may either be synchronous or asynchronous. The power converters convert and transfer power from the electrical generators to the grid as described below.

FIG. 2 shows an electrical system corresponding to rotors of a multi-rotor wind turbine. The electrical system includes electrical generators 202A, 202B, 202C, and 202D (collectively electrical generators 202), machine-side converters (MSCs) 204A, 204B, 204C, and 204D (collectively MSCs 204) (otherwise referred to generator-side converters), LSCs 206A, 206B, 206C, and 206D (collectively LSCs 206) and transformers 208 A, 208B, 208C, and 208D (collectively transformers 208) coupled to a power gird 210. The MSCs 204 and LSCs 206 are connected via direct current (DC) links 212A, 212B, 212C, and 212D (collectively DC links 212).

The electrical generators 202 convert mechanical energy to electrical energy having AC (alternating current) voltage and current (collectively referred to as "AC signals"), and provides the generated AC signals to the MSCs 204. That is, each MSC may be arranged to receive an input AC signal from an electrical generator of one of the plurality of rotors R_n of the multi-rotor turbine. The AC signals from the electrical generator have a variable frequency, due to varying wind. The MSCs 204 convert or rectify the AC signals received from the electrical generators 202 to DC (direct current) voltages and DC currents (collectively know as "DC signals") which are provided to the DC-links 212. The LSCs 206 convert the DC signals from the DC- link 212 into AC signals to be sent to a power grid 210. However, it is normal, under certain conditions, for wind turbines, or rotors, to be supplied with power from the power grid 210, in which case, the the LSC would convert AC signals to DC signals, and the MSC would convert DC signals to AC signals.

The power output of each of the LSCs 206 may be fed to the power grid 210 through transformers 208 configured to adjust a voltage of the AC signals. The transmissions lines from the transformers 208 may be connected directly to the power grid 210 or, if in a wind farm, join with other transmission lines at a point of common connection (PCC) before connecting to the grid.

It should be noted that the electrical system described with reference to figure 1 is only an example of the electrical configuration of a multi-rotor wind turbine and only the main components are shown. The present disclosure should not be limited to the exact electrical system configuration shown in FIG. 1 . Other electrical configurations are possible. For example, the electrical system described with reference to FIG. 1 may include filters between the electrical generators 202 and MSCs 204. Also, there may be switches arranged at various locations for connecting or disconnecting certain components of the turbine, and there may be transducers or transformers at various locations for measurement or metering.

FIGs. 3A and 3B illustrate example configurations of power conversion systems for multi-rotor turbines. Each rotor of the multi-rotor turbine 300 of FIG. 3A may include MSCs 204, LSCs 206 and transformers 208 located in a corresponding nacelle of the each of the rotors R_n.

FIG. 3B illustrates a configuration of a centralized power conversion system for a multi-rotor turbine 301 , in accordance with aspects of the present disclosure. As illustrated, each of the MSCs 204 may correspond to one of the rotors R_n. The outputs of the MSCs 204 may be fed to an LSC 302. By having an LSC 302 that is common to multiple MSCs 204, power loss in the DC link at the output of the MSCs 204 may be reduced as compared to having separate LSCs 206 corresponding to each of the MSCs. Moreover, the bus bar connection from the nacelles to the LSC 302 may be reduced as compared to bus bar connections between nacelles and the LSCs 206.

Moreover, when the DC/AC conversion performed by the LSC 302 is collected in one central unit, the peak to average ratio of the AC signal generated by the LSC 302 may be reduced with a factor of:

where N is the number of nacelles/rotors. In some cases, the reliability of the LSC 302 may be determined by peak loads. With the centralized concept of the present disclosure, peak loads may be reduced, and thus, the reliability of the power conversion system of the multi-rotor turbine can be more predictable and generally increased.

In certain aspects, the LSC 302 may be located in the tower 104. For example, the LSC 302 may be located at the top of the tower, but may also be located in a middle portion (e.g., about half way between the top and bottom of the tower 104), or at the bottom (e.g. , base) of the tower, as described in more detail with respect to FIGs. 4-6. By locating the LSC 302 in the tower, the weight of the nacelles may be reduced as compared to having a designated LSCs 206 for each of the rotors R_n located in respective nacelles 102. This reduces strain on the support bars 106.

In certain aspects, a common transformer 304 may be used to adjust the voltage of an AC signal generated by the LSC 302. By using a single transformer 304 for power conversion of multiple MSCs (e.g. , corresponding to multiple rotors R_n), no load losses of the power conversion system may be reduced. For example, when all transformer functionality is centralized in one single unit, the no-load losses, and hence, consumption of the turbine may be reduced compared with a power conversion system with distributed transformers (e.g. , having a designated transformer for each rotor as illustrated in FIG. 3A).

Moreover, the transformer 304 may be located in the tower 104, further reducing the weight of nacelles 102. Reducing weight of the nacelle/rotor units reduces multi-rotor costs due to the lower gravity loads in the support bars 106. This is important as a twenty percent reduction in weight of nacelles may translate to a cost of energy savings of about one percent.

FIG. 4 illustrates an example power conversion system for a multi-rotor turbine 400 with a common LSC 302 and/or transformer 304 located at the bottom of the tower 104 (e.g. , at the tower base), in accordance with certain aspects of the present disclosure. By locating the LSC 302 and/or transformer 304 at the bottom of the tower 104, the weight of the tower may be reduced. Moreover, more space may be available in the tower for other components. FIG. 5 illustrates an example power conversion system for a multi-rotor turbine

500 with a common LSC 302 and/or transformer 304 located at a middle portion of the tower 104, in accordance with certain aspects of the present disclosure. By locating the LSC and/or the transformer at the middle portion of the tower 104, the LSC and/or transformer may be used as a mass dampener. For example, the LSC 302 and/or transformer 304 may be used to dampen eigenmodes (e.g. , the natural vibrations of the multi-rotor turbine). That is, the LSC 302 and/or transformer 304 may be used as a tower passive vibration damper in a spring-mass system which may, for example, dampen second eigenmode vibrations. In certain aspects, the LSC 302 and/or transformer 304 may be located at a top portion of the tower 104, which can also dampen vibrations.

An advantage of the embodiment of FIG. 5 is that the increased proximity will reduce the electrical cabling cost and losses compared to an embodiment with a pure down tower location. In a further embodiment the LSC 302 and/or transformer 304 is installed in a location above the lower support bars 106C and 106D, but below the support bars 106A and 106B. In particularly the location is the geometric center of the plane formed by the centers of the four rotors R1 , R2, R3 R4.

In another embodiment the location and mass of the LSC and/or transformer can be tailored to provide a secondary benefit of changing the tower frequencies and assist in managing the dynamics of tower vibrations.

From a cooling perspective the location of the LSC 302 and/or transformer 304 between the rotors ensures that the freshest cooling air flows by the tower midsection. The LSC 302 is installed in an enclosure, where the enclosure itself can comprise walls with heat exchanging effects. The effect is utilized even further if the LSC and / or transformers are arranged outside the tower on a platform surrounding the tower.

In an embodiment the LSC and/or transformer is installed at outside wall of the tower above the lower support bars, perhaps resting on a platform, such platform also provide work space for service.

In a further embodiment the LSCs have heat exchange module(s) which are installed on the outside tower wall. In an embodiment there is a tower mid-section where the LSCs and / or transformer are pre-installed prior to erecting the tower 104. Such a section can be a standard tower section or a shorter section having only the height of the LSCs and peripherals.

The platform and or mid tower section can for fixed or attached together with the yaw system of the lower rotors R3 and R4. I.e. the LSC would rotate around a bearing mounted on the bottom tower section. An advantage of such, would allow the tower sections, yawing together with the rotors, to be optimized for a uni-directional loading, since the tower sections mostly sees a predictable directional loading from the wind.

For all the embodiments with the LSC(s) installed on the outside tower walls, it applies that the LSC can be made with a cover or shroud shaped to accelerate the air flow into the rotors.

FIG. 6 illustrates an example power conversion system for a multi-rotor turbine 600 with MSCs 204 located in the tower 104, in accordance with certain aspects of the present disclosure. That is, instead of locating the MSCs 204 in the nacelles 102, the MSCs 204 may be located in the tower 104 to further reduce the weight of the nacelles. The complexity of the power conversion system for the multi-rotor turbine may be reduced by placing the MSCs 204 in the tower 104. That is, by having a central location (e.g. , in the tower 104) for the MSCs 204, the MSCs 204 can be serviced (e.g., repaired) more easily. In certain aspects, the MSCs 204 may also be located at the bottom of the tower 104. In certain aspects, a switchgear for the power conversion systems of FIG.s 3A, 4, 5, and 6 may be located at a bottom of a respective tower 104.

FIG. 7 illustrates an example power conversion system with a DC chopper/resistor placed in the DC link between MSCs 204 and LSC 302, in accordance with certain aspects of the present disclosure. A DC chopper may be used to capture the surplus of power from the rotors and corresponding MSCs 204. If a failure is incurred with respect to a nacelle of the multi-rotor turbine, energy from the failing rotor may be absorbed by the DC chopper while the failing rotor is shut down. This allows for the failing rotor to be shut down gently avoiding high thrust loads on the structure of the multi-rotor turbine. This also applies to multi-rotor turbines using double-fed inductor generators (DFIG).

FIG. 8 illustrates example operations 800 for assembly of a multi-rotor turbine, in accordance with aspects of the present disclosure. The operations 800 begin, at 802, by providing a plurality of machine-side converters (MSCs), each configured to receive an alternating current (AC) input signal from one of a plurality of rotors of a multi-rotor turbine and generate a DC signal based on the input AC signal. At 804, the operations further include providing a line-side converter (LSC) configured to receive the DC signals from each of the plurality of MSCs and generate an output AC signal based on the DC signals. At 806, the operations 800 include coupling outputs of the MSCs to the LSC.

In certain aspects, the operations 800 may also include providing a transformer configured to adjust a voltage of the output AC signal and provide the voltage adjusted output AC signal to a power grid coupled to the multi-rotor turbine. In this case, the transformer may be located in a tower of the multi-rotor turbine. In certain aspects, the transformer may be located at a bottom of a tower of the multi- rotor turbine. In other aspects, the transformer may be located at a middle portion (e.g., about half way between the top and bottom) of the tower.

In certain aspects, the LSC may be located in a tower of the multi-rotor turbine. In some cases, the LSC may be located at a bottom (e.g. , base) of a tower of the multi-rotor turbine. In certain aspects, each of the MSCs may be located in a tower of the multi-rotor turbine. In certain aspects, the operations 800 my further include providing a DC chopper coupled in series in a DC link between the MSCs and the LSC. While examples provided herein have described a centralized power conversion system with respect to a multi-rotor turbine with four rotors to facilitate understanding, the techniques described herein can be applied to a multi-rotor turbine having any number of rotors. For example, aspects of the present disclosure may be implemented with a multi-rotor turbine with eight rotors, where a common LSC and/or transformer is shared by each of the eight rotors (and corresponding eight MSCs) of the multi-rotor turbine.

In certain aspects, rotors of a multi-rotor turbine can be separated into groups and each of the groups of rotors may share a separate LSC and/or transformer. For example, rotors of a multi-rotor turbine with eight rotors may be separated into two groups of rotors, each with four rotors. A first LSC and/or transformer may be shared by the four rotors of the first group, and a second LSC and/or transformer may be shared by the four rotors of the second group. The size of each group (e.g., the number of rotors in the group) may be selected based on cost, power, and complexity considerations. For example, the cost of two LSCs and/or transformers that can each support four rotors may be less than a single LSC and/or transformer that can support eight rotors. As another example, the power rating of an LSC and/or transformer may be limited, therefore, the rotors of a multi-rotor turbine may be separated into groups, such that each LSC and/or transformer can support the power specifications of the rotors in the respective group.

In certain aspects, the centralized power conversion system of the present disclosure can be used as a redundancy measure for a de-centralized power conversion system as described with respect to FIG. 2 and FIG. 3A. For example, while each of a group of rotors of a multi-rotor turbine may include its own designated LSC and/or transformer, each of the LSCs and/or transformers may also be configured to operate as a common LSC and/or transformer for multiple rotors.

Therefore, a multi-rotor turbine may operate according to the de-centralized concept of FIGs. 2 and 3A during normal operations. However, if an LSC and/or transformer designated to a rotor of the multi-rotor turbine experiences a failure, power to the failing LSC and/or transformer may be transferred to another LSC and/or transformer of a different rotor (e.g., one with sufficient capacity to handle the extra power). In other words, once the power is transferred to the other LSC and/or transformer, the other LSC operates as a common LSC and/or transformer for both its own designated rotor and the rotor with the failing LSC and/or transformer. In this manner, the multi-rotor turbine may remain in operation while the failing LSC and/or transformer is repaired.

In the preceding, reference is made to aspects presented in this disclosure. However, the scope of the present disclosure is not limited to specific described aspects. Instead, any combination of the preceding features and elements, whether related to different aspects or not, is contemplated to implement and practice contemplated aspects. Furthermore, although aspects disclosed herein may achieve advantages over other possible solutions or over the prior art, whether or not a particular advantage is achieved by a given aspect is not limiting of the scope of the present disclosure. Thus, the preceding aspects, features, and advantages are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to "the invention" shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in a claim(s).

As will be appreciated by one skilled in the art, the aspects disclosed herein may be embodied as a system, method, or computer program product. Accordingly, aspects may take the form of an entirely hardware aspect, an entirely software aspect (including firmware, resident software, micro-code, etc.) or an aspect combining software and hardware aspects that may all generally be referred to herein as a "circuit," "module," or "system." Furthermore, aspects may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon. Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.

Aspects of the present disclosure are described above with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to aspects presented in this disclosure. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks. The flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various aspects. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

In view of the foregoing, the scope of the present disclosure is determined by the claims that follow.

Claims

1 . A multi-rotor turbine, comprising:

a plurality of machine-side converters, MSC, each configured to:

receive an input alternating current, AC, signal from one of a plurality of rotors of the multi-rotor turbine; and

generate a DC signal based on the input AC signal; and

a line-side converter, LSC, configured to:

receive the DC signals from each of the plurality of MSCs; and generate an output AC signal based on the DC signals.

2. The multi-rotor turbine of claim 1 , further comprising a transformer configured to adjust a voltage of the output AC signal and provide the voltage adjusted output AC signal to a power grid coupled to the multi-rotor turbine.

3. The multi-rotor turbine of claim 2, wherein the transformer is located in a tower of the multi-rotor turbine.

4. The multi-rotor turbine of claim 2 or 3, wherein the transformer is located at a base of a tower of the multi-rotor turbine.

5. The multi-rotor turbine of claim 2 or 3, wherein the transformer is located about half way between a top and a bottom of a tower of the multi-rotor turbine.

6. The multi-rotor turbine of any of claims 1 to 5, wherein the LSC is located in a tower of the multi-rotor turbine.

7. The multi-rotor turbine of any of claims 1 , wherein the LSC is located about half way between a top and a bottom of a tower of the multi-rotor turbine.

8. The multi-rotor turbine of claim 7, wherein the LSC is located about half way between a top and a bottom of a tower of the multi-rotor turbine, at an outer side of the tower, wherein the LSC is located at a platform, surrounding the tower.

9. The multi-rotor turbine of any of claims 1 to 6, wherein the LSC is located at a base of a tower of the multi-rotor turbine.

10. The multi-rotor turbine of any of claims 1 to 7, wherein each of the MSCs are located in a tower of the multi-rotor turbine.

1 1 . The multi-rotor turbine of any of claims 1 to 8, further comprising a DC chopper coupled in series in a DC link between the MSCs and the LSC.

12. The multi-rotor turbine of any of claims 1 to 9, further comprising:

another plurality MSCs, each configured to:

receive another input AC signal from one of another plurality of rotors of the multi-rotor turbine; and

generate another DC signal based on the other input AC signal; and another LSC configured to:

receive the other DC signals from each of the plurality of other MSCs; and

generate another output AC signal based on the other DC signals.

13. The multi-rotor turbine of any of claims 1 to 10, wherein the LSC is one of a plurality of LSCs, wherein each of the plurality of LSCs is configured to receive a DC signal of the plurality of DC signals.

14. A power generation system, comprising:

a plurality of multi-rotor turbines coupled to a power grid, wherein each multi- rotor turbine of the plurality of multi-rotor turbines comprises:

a plurality of machine-side converters, MSCs, each configured to:

receive an input alternating current, AC, signal from one of a plurality of rotors of a respective multi-rotor turbine of the plurality of multi-rotor turbines; and

generate a DC signal based on the input AC signal; and a line-side converter, LSC, configured to:

receive the DC signals from each of the plurality of MSCs; and generate an AC output signal based on the DC signals; and a transformer coupled to a power grid, and configured to:

adjust a voltage of the output AC signal; and provide the voltage adjusted output AC signal to the power grid.

15. The power generation system of claim 12, wherein the LSCs are located in a tower of a respective multi-rotor turbine of the plurality of multi-rotor turbines.

16. The power generation system of claim 12 or 13, wherein each of the MSCs are located in a tower of a respective multi-rotor turbine of the plurality of multi-rotor turbines.

17. The power generation system of any of claims 12 to 14, wherein the transformers are located in a tower of a respective multi-rotor turbine of the plurality of multi-rotor turbines.

18. A method of assembly of a multi-rotor turbine, comprising:

providing a plurality of machine-side converters, MSCs, each configured to: receive an alternating current, AC, input signal from one of a plurality of rotors of a multi-rotor turbine; and

generate a DC signal based on the AC input signal; and

providing a line-side converter, LSC, configured to:

receive the DC signals from each of the plurality of MSCs; and generate an output AC signal based on the DC signals; and coupling outputs of the MSCs to the LSC.