CABINET FOR WIND TURBINES

Technical Field The present invention relates generally to a power converter cabinet assembly for a wind turbine. More specifically, the present invention relates to air cooling apparatus for a power converter assembly for a wind turbine, and to an associated nacelle comprising the power converter cabinet assembly. Background

Wind turbines generators are commonly connected to an electrical grid via power converters, in order to control the supply of electrical energy to the electrical grid. In particular, power converters are employed to adjust the variable-frequency power produced by an electrical generator of the wind turbine generator, so as to supply the electrical grid with a substantially constant frequency and voltage. The use of power converters is particularly well known in the case of wind turbines having a capacity of the order of megawatts. Summary of Aspects of the Invention

Power converters may typically be enclosed in a cabinet that may be situated in a nacelle of the wind turbine generator. In general, such a cabinet contains all of the electrical components required to convert the single-phase or three-phase alternating current produced by the electrical generator into direct current. In a subsequent stage, the direct current is converted into a second single-phase or three-phase alternating current for supplying to the electrical grid. The electrical components and modules necessary to perform the conversion may include busbars, line side converters, machine side converters, harmonic filters and breaker modules.

During operation of the power converter, it is common for the electrical components of the converter to heat up. In order to maintain a suitable operating temperature within the cabinet, and to prevent overheating of the electrical components, converter cabinets may comprise some form of cooling arrangement. Prior art cooling systems include fan arrangements, the fans being positioned around the cabinet so as to drive air into the converter cabinet from the external environment, circulating the cooling air around the electrical components.

In these prior art arrangements, the cooling air can be influenced by external conditions, and may contain contaminants that are present outside of the nacelle. These contaminants can be introduced into the converter cabinet via the fans, and may damage the electrical components of the power converter or the mechanical components of the fan arrangement. Any such damage can be difficult to access and repair, and may require replacement of the entire converter cabinet. Furthermore, the distributed configuration of the cooling components is not an efficient use of space, and has complex electrical installation.

Embodiments of the invention aim to overcome some or all of these problems. In accordance with one aspect of the invention, there is provided a power converter cabinet assembly for a wind turbine generator, the power converter cabinet assembly comprising: a main housing defining an interior space for a plurality of electrical components, and a base on which the main housing is mounted. The base comprises air cooling apparatus configured to cool the interior space of the main housing via a flow interface between the base and the main housing.

The air cooling apparatus is advantageously located in the base of the power converter assembly, and is separated from the electrical components of the main housing. This allows for the air cooling apparatus to be repaired or replaced without requiring access or modification to the main housing of the power converter. Since the main housing accommodates the plurality of electrical components, the arrangement thus reduces exposure of the electrical components to an environment external to the power converter assembly, relative to existing arrangements. The power converter assembly of embodiments of the invention both increases ease of maintenance of the air cooling apparatus, and minimises a risk of damage to the plurality of electrical components.

The power converter cabinet assembly may be configured to define an internal air flow path defined at least in part by the flow interface. The internal air flow path may be isolated from an external environment of the power converter cabinet assembly. Advantageously, the internal air flow path may therefore be isolated from pollution and/or contaminants in the external environment, guarding against damage to the electrical components of the power converter cabinet assembly.

Optionally, the air cooling apparatus may comprise an air-to-air heat exchanger arrangement defining one or more flow zones. Each of the one or more flow zones of the heat exchanger arrangement may comprise a primary air flow path defining a portion of the internal air flow path and secondary air flow path defining a portion of an external air flow path. In one embodiment, the heat exchanger arrangement may be configured so that the one or more secondary air flow paths is selectively restricted in order to control the heat energy transfer of the heat exchanger arrangement. Each of the flow zones may be associated with a respective group of one or more compartments of the main housing. In this case, heat energy transfer of the heat exchanger arrangement may be controlled to be different in each of the flow zones, to account for expected differences in temperature variation between the respective groups of one or more compartments.

In one example, the base may house an internal fan to drive air flow around the internal air flow path. In this case, the internal fan may be accessible from the interior space of the main housing.

A speed of the internal fan may be controlled in dependence on one or more temperature values and one or more humidity values associated with the interior space of the main housing. In one embodiment, a speed of the internal fan may be controlled to maintain a relative humidity value associated with the interior space of the main housing at or below a predetermined threshold level. Alternatively, or additionally, a speed of the internal fan may be controlled in dependence on an amount of power supplied from the power converter cabinet assembly to the electrical grid. In one embodiment, the power converter cabinet assembly may further comprise a duct, wherein the duct houses an external fan to drive air flow around the external air flow path. The external fan may be accessible through the duct. Such an arrangement advantageously allows for maintenance and repair of the external fan to be carried out without requiring access to the interior space of the main housing, minimising the risk of damage to the plurality of electrical components. Optionally, a speed of the external fan may be controlled in dependence on a temperature difference between the external air flow path and the interior space of the main housing. The speed of the external fan may be reduced in the event that the temperature difference falls below a predetermined threshold level. Beneficially, the power consumed in driving the external fan is thus reduced in the event that the temperature difference is insufficient for effective cooling of the interior space.

According to another aspect of the invention, there is provided a nacelle for a wind turbine, comprising a power converter cabinet assembly in accordance with a previous aspect of the invention.

According to another aspect of the invention, there is provided a wind turbine generator comprising a power converter assembly in accordance with a previous aspect of the invention.

Brief Description of the Drawings

Figure 1 is a perspective view of a wind turbine comprising a power converter cabinet assembly according to an embodiment of the invention;

Figure 2 is a more detailed perspective view of an embodiment of the power converter cabinet assembly of Figure 1 ;

Figure 3a is a schematic view of the power converter cabinet assembly of Figure 2;

Figure 3b is a schematic view from above of the power converter cabinet assembly of Figure 2;

Figure 4 is a perspective view of a base of the power converter cabinet assembly of Figure 2;

Figure 5 is an enlarged perspective section view of part of the base of Figure 4;

Figure 6 is a plan view of an external air flow path passing through the base of the power converter cabinet assembly; Figure 7 is a perspective view similar to that of Figure 5, showing the external air flow path illustrated in Figure 6 from a different viewing angle; and

Figure 8 is a schematic internal view of the converter cabinet assembly showing an internal air flow path.

Detailed Description

Figure 1 shows a perspective view of a wind turbine generator 2 having a tower 4, a nacelle 6 and a hub (not shown) supporting three wind turbine blades 8, as is conventional. Other configurations of wind turbine generators are known. The nacelle 6 comprises a number of components for controlling operation of the wind turbine generator 2, including a power converter cabinet assembly 10. The power converter cabinet assembly 10 comprises components for converting typically a three-phase alternating voltage produced by an electrical generator into a controlled three-phase output voltage for supplying to the electrical grid. In this way, the components of the power converter cabinet assembly 10 are configured to adjust the variable-frequency electrical power supplied by the electrical generator of the wind turbine generator 2 to produce a substantially constant frequency and voltage of supply, as required by the electrical grid.

As shown in Figure 2, the power converter cabinet assembly 10 comprises a converter cabinet 1 1 , having a main housing 12 and a base frame 14, or base, on which the main housing 12 is mounted. The main housing 12 and the base frame 14 thus form an upper and lower portion of the converter cabinet 1 1 , respectively, such that the base frame 14 serves as the foundation of the converter cabinet 1 1 , supporting the structure of the main housing 12. The main housing 12 comprises a base, or floor 16, a front wall 18, a rear wall 20 (shown in Figure 3b), a left side wall 22 (shown in Figure 3a) and a right side wall 24, in the orientation of the figure.

Referring to Figures 3a and 3b, the main housing 12 of the converter cabinet 1 1 defines an interior space 26 for housing a plurality of electrical components that are configured to operate as a power converter 28 for the wind turbine generator 2. As is conventional, the plurality of electrical components may be arranged in a series of enclosures or compartments according to function. The compartments may be arranged substantially in the order and direction of power transfer from the electrical generator of the wind turbine generator 2 to the electrical grid.

In the embodiment depicted in Figures 3a and 3b, a right-hand portion of the main housing 12, towards the right side wall 24, corresponds to a machine side of the power converter 28. A left-hand portion of the main housing 12, towards the left side wall 22, corresponds to a grid side of the power converter 28. In this example, the compartments are arranged substantially in order of power transfer from a right-hand side of the main housing 12 to a left hand side of the main housing 12. Three compartments may be positioned on a right-hand side of the main housing 12 that are associated with a machine side converter (MSC) 30 of the power converter 28. Three compartments associated with a line side converter (LSC) 32 of the power converter 28 may be similarly arranged, towards a left-hand side of the main housing 12 relative to the compartments of the MSC 30. The MSC compartment 30 and the LSC compartment 32 may contain respective power electronic modules 34 comprising electronic switches for controlling the timing of electrical signals of the power converter 28. Between the MSC compartment 30 and LSC compartment 32 may be provided a control unit compartment 36, within which electrical components associated with control of the power converter 28 are housed. In particular, the control unit compartment 36 may house a power controller 38 for linking with a plurality of temperature sensors 40 and heating elements 42 of the power converter cabinet assembly 10.

In order to facilitate power transfer, a DC link 44 may be provided that bridges across the three of each of the MSC compartments 30 and LSC compartments 32. At the left-hand side of the main housing 12 additional electrical components associated with the power converter 28 may be provided in further compartments. These additional compartments may include breaker electronics 46 for controlling connection of the power electronic modules 34 of the MSC 30 and the LSC 32 to an electrical generator, and to the electrical grid, respectively. The additional components may further include auxiliary electrical components housed within an auxiliary cabinet 48, for example charging electronics for providing power to the DC link 44.

As in the embodiment depicted in Figures 3a and 3b, a compartment for harmonic filters 50 may be positioned towards the left-hand side of the main housing 12 that is configured to reduce switching noise generated by the power electronic modules 34. A busbar 52 may be provided to allow power transfer between the compartments of the LSC 32 and the auxiliary electrical components, the harmonic filters 50 and the breaker electronics 46. Each of the compartments of the main housing 12 extends substantially from the front wall 18 to the rear wall 20 of the main housing 12. In the illustrated embodiments the electrical components are housed in a plurality of cabinet compartments that can be subdivisions of the main housing 12. However, this is not essential. The components could instead be housed in a single undivided volume corresponding to the interior space 26. Referring to Figures 4 and 5, the base frame 14 has a front wall 54, a rear wall 56 and a base 58. The base frame 14 houses components arranged to control the climate within the main housing 12 of the converter cabinet 10. In overview, these components may include: air cooling apparatus 60; liquid cooling apparatus 62; and an internal fan 64. A flow interface 66 exists between the base frame 14 and the main housing 12, across which air to and from the air cooling apparatus 60 is able to pass. In broad terms the flow interface is defined in the region where the base frame 14 and the main housing 12 meet. For example, the floor 16 of the main housing may be open or air permeable to allow air flow to pass between the main housing 12 and the base frame, as will become apparent in the following discussion.

As is most clearly shown in Figures 6 and 7, an opening at a central region of the front wall 54 of the base frame 14 defines an inlet 68 of the base frame 14. The base frame 14 is further provided with an outlet 70, which provides an opening on the rear wall 56 of the base frame 14, as shown in Figure 6. Alternatively, or additionally, the outlet 70 may provide an opening on the base 58 of the base frame 14, towards the rear wall 56. The outlet 70 is positioned substantially in line with the inlet 68 in a longitudinal direction of the base frame 14. A separate duct 72 is positioned next to the front wall 54 of the base frame 14, and serves to house an external fan 74. The duct 72 is provided with an inlet 76 and an outlet 78, and is positioned such that the outlet 78 of the duct 72 is in fluid communication with the inlet 68 of the base frame 14. A filter (not shown) may be positioned at the boundary between the duct 72 and the base frame 14.

Referring again to Figures 4 and 5, the liquid cooling apparatus 62 of the base frame 14 is controlled and arranged so as to cool the power electronic modules 34 in the MSC LSC compartments 30, 32. The liquid cooling apparatus 62 comprises an inlet flow pipe 80, a return flow pipe 82 and an arrangement of liquid cooling hoses 84. The inlet and return flow pipes 80, 82 are arranged to run substantially horizontally in line with an upper end of the front wall 54 of the base frame 14, transporting cooling liquid along the length of the power converter cabinet assembly 10. The inlet and return flow pipes 80, 82 connect to the power electronic modules 34 of both the LSC 32 and the MSC 30 by way of the liquid cooling hoses 84 running vertically upwards from the pipes 80, 82. The arrangement of the liquid cooling apparatus 62 is not central to the invention, and so will not be described in further detail here. However, note that suitable fluid pumps and fluid coolers may be arranged in the base frame 14 in addition to the air cooling apparatus 60 which provides for a convenient and space efficient arrangement.

The air cooling apparatus 60, internal fan 64 and external fan 74 serve to maintain the electrical components of the power converter 28 within a suitable operating temperature range, so as to avoid overheating of the components. This suitable operating temperature range may be from around 0°C to around 55°C. The main housing 12 comprises temperature sensors 40 (shown in Figure 3a) that are configured to monitor a temperature of the interior space 26 of the main housing 12. The temperature sensors 40 are arranged so as to record the temperature associated with each of the compartments of electrical components, allowing intelligent control of the internal fan 64 and the external fan 74. Measurement data from the temperature sensors 40 is transmitted to the power controller 38 of the control unit compartment 36 (shown in Figure 3a), and the electrical components of the control unit compartment 36 are configured to control the internal fan 64 and the external fan 74 in response.

The air cooling apparatus 60 comprises an air-to-air heat exchanger arrangement 86, having a plurality of aluminium heat exchangers 88, as is conventional. The heat exchanger arrangement 86 extends along substantially the entire length of the base frame 14 and across the entire width of the base frame 14 so that they take up a substantial volume of the base frame 14. Since the main housing 12 of the converter cabinet 11 directly overlies the base frame 14, the heat exchanger arrangement 86 thus extends along a substantial length, and across a substantial width, of the main housing 12. Such an arrangement ensures that the heat exchangers 88 are positioned to effect cooling across a large volume of the converter cabinet 1 1 , and are thus arranged to cool the electrical components most effectively. The air-to-air heat exchanger arrangement 86 defines a plurality of flow zones that in general correspond to the location of different groups of compartments. In the illustrated embodiment, the heat exchanger arrangement 86 defines three flow zones: firstly, a zone 90 corresponding to and positioned beneath the auxiliary cabinet 48 and breaker electronics 46; secondly, an LSC zone 92, corresponding to and positioned beneath the LSC compartments 32; and thirdly, an MSC zone 94, corresponding to and positioned beneath the MSC compartments 30. The internal fan 64 is positioned on the base 68 of the base frame 14, between the LSC zone 92 and the MSC zone 94 of the heat exchanger arrangement 86.

The power converter cabinet assembly 10 comprises two separate air flow paths: an internal air flow path 96 (shown in Figure 8); and an external air flow path 98 (shown in Figure 6) that is separate from the internal air flow path 96. Both air flow paths 96 and 98 flow through the heat exchanger arrangement 86, albeit in different directions, and are separated from one another such that the air flow in the external air flow path 98 acts to cool the air flowing along the internal air flow path 96.

In order to guide the flow of air within the air flow paths 96, 98 through the base frame 14, the base frame 14 comprises three channels. In particular, the base frame 14 comprises an air return channel 100 of the internal air flow path 96. The air return channel 100 is positioned beneath the heat exchangers 88 of the heat exchanger arrangement 86, and runs along the entire length of the heat exchangers 88, so as to direct the flow of air within the internal air flow path 96 towards the internal fan 64. The air return channel 100 is divided into two longitudinal sections that are separated by the internal fan 64: a first section 106 (shown in Figure 7) corresponding to the auxiliary cabinet and breaker cabinet zone 90 and the LSC zone 92 of the heat exchanger arrangement 86; and a second section 108 corresponding to the MSC zone 94 of the heat exchanger arrangement 86. The first and second sections 106, 108 of the air return channel 100 open into a volume of the base frame 14 corresponding to the position of the internal fan 64. The base frame 14 further comprises an inlet channel 102 of the external air cooling path 98 and an exhaust channel 104 of the external air cooling path 98. The inlet channel 102 and the exhaust channel 104 are positioned either side of the heat exchanger arrangement 86, and are divided from the air return channel 100 by way of two C-shaped brackets 110, which together form a conduit defining the air return channel 100. Air within the external air flow path 98 is distributed along the length of the inlet channel 102, prior to passing through the heat exchangers 88 of the heat exchanger arrangement 86. The air is collected in the exhaust channel 104. The inlet and exhaust channels 102, 104 are thus in fluid communication with one another through the heat exchanger arrangement 86, and run along substantially the entire length of the heat exchanger arrangement 86.

Figures 6 and 7 show schematic views of the external air flow path 98 passing through the base frame 14 of the converter cabinet 11. During operation of the power converter 28, the external fan 74 is configured to draw cool air into the inlet 76 of the duct 72 from the nacelle 6, driving air substantially horizontally along the inlet channel 102. The external fan 74 creates a pressure difference across the heat exchangers 88, such that the air pressure in the in the inlet channel 102 is greater than the air pressure in the exhaust channel 104. Air within the external air flow path 98 thus passes from the inlet channel 102 and through the heat exchangers 88, where energy is transferred from the relatively warm air flow of the internal air flow path 96 to the relatively cool air of the external air flow path 98, thus increasing the temperature of the external air flow. The warmed air passes into the exhaust channel 104, where the air is collected before passing through the outlet 70 of the base frame 14.

Referring to Figure 8, in contrast, the internal air flow path 96 is a closed cooling loop, arranged to circulate air around the interior space 26 of the main housing 12 by way of the internal fan 64, cooling the electrical components of the power converter 28. The internal air flow path 96 is sealed from the environment of the nacelle 6, such that the interior space 26 of the main housing 12 is protected from the external environment. This makes it possible to maintain a substantially constant temperature within the main housing 12, and guards against the ingress of contaminants into the compartments of electrical components, preventing resultant damage to the components.

The floor 16 of the main housing 12 is permeable, to enable air flow to pass across the flow interface 66 between the base frame 14 and the main housing 12. The internal air flow path 96 extends from the base frame 14, through the floor 16 and into the main housing 12 of the converter cabinet 11 , circulating air around the interior space 26 of the main housing 12. Cool air within the internal air flow path 96 is driven vertically through the control unit compartment 36 by way of the internal fan 64, passing upwards through the control unit compartment 36 to an upper end of the main housing 12. From here, the internal air flow path 96 splits into two different directions and cool air is distributed substantially horizontally along the entire length of the main housing 12 through the compartment corresponding to the busbar 52. The air flow runs towards the left side wall 22 of the main housing 12 over the top of the LSC compartments 32, and also towards the right side wall 24 of the main housing 12 over the top of the MSC compartments 30. The air is subsequently circulated downwardly through the MSC compartments 30, the LSC compartments 32 and the compartments corresponding to the breaker electronics 46, the auxiliary cabinet 48 and the harmonic filters 50. While the power converter 28 is operational, the electrical components stored within the main housing 12 warm up. Power dissipation within each of the compartments differs, and electrical components within the compartments warm up to differing extents while the converter 28 is operational. The supply of air to each of the compartments may therefore be controlled to account for this variation in power dissipation, so that more air may be supplied to those electrical components having the greatest power dissipation. For example, on the grid side of the main housing 12, a larger volume of air may be passed through the busbar 52 and the auxiliary cabinet than through the harmonic filter 50. The volumetric air flow to different compartments may be controlled physically by controlling air flow apertures into those compartments.

Heat energy from the electrical components is transferred to the air flowing through the internal air flow path 96 as it passes across the main housing 12 and down through the compartments of the main housing 12, thus warming the air. Since the floor 16 of the main housing 12 is permeable, for example, by being an open grid, upon reaching the base frame 14 of the converter cabinet 11 , the warm air of the internal air flow path 96 passes vertically down through the heat exchangers 88 of the heat exchanger arrangement 86. A primary air flow path 112 defines a portion of the internal air flow path 96 that passes through the heat exchanger arrangement 86. A secondary air flow path 114 (shown in Figure 6) defines a portion of the external air flow path 98 that passes through the heat exchanger arrangement 86. In one embodiment, each of the flow zones 90, 92, 94 of the heat exchanger arrangement 86 comprises a primary and a secondary air flow path 112, 114.

As is known, air-to-air heat exchangers operate by passing two separate streams of air past a heat conductive surface. The heat energy from the relatively warm air is thus transferred to the stream of relatively cool air, which acts to cool the warmer stream. Therefore, the heat exchangers 88 effect the transfer of energy from the air of the primary air flow path 1 12 and to the air of the secondary air flow path 114. A temperature gradient thus exists across the heat exchangers 86 for each of the internal and external air flow paths 96, 98, and the air of the internal air flow path 96 is cooled as it passes through the heat exchangers 88. The cooled air is driven into the first and second sections 106, 108 of the air return channel 100 beneath the heat exchanger arrangement 86, and is drawn from the air return channel 100 into the internal fan 64 positioned beneath the control unit compartment 36. The air continues to circulate throughout the internal air flow path 96 while the power converter 28 is operational.

As previously described, control of the internal fan 64 and the external fan 74 may be managed by the power controller 38, in response to measurements associated with the temperature sensors 40 mounted in the main housing 12. The fans 64, 74 of the internal and external air flow paths 96, 98 may be configured to control the volumetric flow rates of air through the internal and external air flow paths 96, 98, respectively. The internal and external fans 64, 74 may be controlled to maintain the temperature within the main housing 12 at a pre-set temperature target, for example around 15°C.

Referring to Figure 3a, the control unit compartment 36 may comprise a humidity sensor 116 that is configured to measure the relative humidity inside the control unit compartment 36. The external fan 74 may be controlled in response to measurements from the humidity sensor 116. For example, the external fan speeds may be controlled to maintain the relative humidity inside the control unit compartment 36 at or below 70%. While the internal and external fans 64, 74 may be controlled to adjust the temperature within the main housing 12 towards the pre-set temperature target, control of the fans 64, 74 may thus depend in part on the measured relative humidity.

The internal fan 64 and external fan 74 may additionally be controlled to maintain any temperature changes within the internal air flow path 96 at or below a predetermined temperature threshold. In order to meet the temperature requirements of the power converter cabinet assembly 10, the internal fan 64 may maintain a minimum air flow of around 5100 m ³ /h within the internal air flow path 96. Preferably, the internal fan 64 maintains an internal flow of around 6000 m ³ /h. It should be appreciated that these values are merely intended as examples and should not be considered to be limiting. The speed of the internal fan 64 may be controlled to be substantially constant. Alternatively, the speed of the internal fan 64 may be controlled in dependence on the temperature of the electrical components of the power converter 28, and, in particular, on the temperature of the components that are expected to experience the greatest temperature increase during operation of the power converter 28. Table 1 below shows the speed of the internal fan 64 as a function of the temperature of electrical components in the main housing 12, where the speed of the internal fan 64 is shown as a percentage of the maximum recommended internal fan speed. Table 1

By way of further explanation, the power controller 38 may control the internal fan 64 to run at 20% maximum recommended internal fan speed in the event that a temperature associated with any of the LSC or MSC power electronic modules 34, the DC link 44 or the control unit compartment 36 reaches the corresponding temperature t1 , as recorded by the temperature sensors 40. However, the internal fan speed may be increased up to maximum based on the increasing measured temperatures at the various sensors 40. The maximum fan speed may correspond to the measured temperatures t2 in the above table.

Alternatively, the internal fan speed may be controlled in dependence on an amount of power delivered from the power converter 28 of the wind turbine generator 2 to the electrical grid. The amount of power supplied by the power converter 28 may be indicative of a level of power dissipation within the compartments of the power converter 28 during operation, and the internal fan speed may be controlled to increase in response to an increase in power delivered to the electrical grid. The speed of the external fan 74 may be controlled to be substantially constant. Alternatively, the power controller 38 may control the external fan 74 in dependence on the temperature within the converter cabinet 11 , as measured by the temperature sensors 40. For example, the external fan speed may be increased up to a maximum as the cabinet temperature approaches a threshold level. Additionally, or alternatively, the external fan speed may be controlled in dependence on a temperature difference between a temperature associated with the external air flow loop 98 and the cabinet temperature. For example, in the event that the temperature difference falls below a threshold value, it may be determined that energy transfer across the heat exchanger arrangement 86 will be insufficient for cooling of the converter cabinet 11 , and the external fan speed may be reduced.

The external fan speed may be reduced in response to an increase in humidity within the converter cabinet 1 1. Reducing the external fan speed may lower the volumetric flow rate through the external air flow path 98, reducing the heat energy transfer potential to the external air flow path 98 and reducing a cooling rate within the converter cabinet 1 1 so as to lower the relative humidity.

Referring again to Figure 6, air flow within the external air flow path 98 is controlled so that the flow is distributed appropriately through between the three flow zones 90, 92, 94 of the air-to-air heat exchanger arrangement 86. The LSC compartment 32 is responsible for a significant proportion of the heat dissipation within the main housing 12 and so the external air flow path 98 may be configured so that about half of the air flow is directed through the LSC zone 92 of the heat exchanger arrangement 86. For example, around 25% of the air flow within the external air flow path 98 may be directed through the zone 90 corresponding to the auxiliary cabinet 48 and the breaker electronics 46, around 50% of the air flow may be directed through the LSC zone 92, and around 25% of the air flow may be directed through the MSC zone 94. The distribution of air flow through the flow zones 90, 92, 94 of the heat exchanger arrangement 86 may be controlled by way of air flow restriction in the exhaust channel 104 of the base frame 14. Air flow restriction may be through mechanical means, such as a physical grill or valve that restricts the air flowing to the outlet 70 of the base frame 14 from each of the flow zones 90, 92, 94 of the heat exchanger arrangement 86. Such restrictions modify the air pressure of the external air flow path 98 within the exhaust channel 104, such that the zones 90, 92, 94 having greater air flow restriction have a lower pressure difference across the heat exchanger arrangement 86 and, thus, a lower air flow rate through the secondary air flow path 114.

In addition to the liquid cooling apparatus 62 and air cooling apparatus 60, the power converter cabinet assembly 10 may comprise preheating apparatus. The preheating apparatus can be used for controlling the temperature and humidity of the interior space 26 of the main housing 12 prior to operation of the power converter 28, such that the environment is suitable for the electrical components of the power converter 28. In particular, the preheating apparatus may include a plurality of heating elements 42 that are distributed around the main housing 12 of the converter cabinet 1 1.

Referring again to Figure 3a, the humidity sensor 116 of the control unit compartment 36 may be configured to measure the relative humidity inside the control unit compartment 36 while the power controller 38 is not fully operational. The humidity sensor 116 may be a mechanical hygrostat. The humidity sensor 116 is complementary to the temperature sensor 40 of the control unit compartment 36 and may provide measurements to an environmental controller 1 18 which is able to monitor the environmental temperature of the control unit compartment 36 before the power controller 38 is powered up. The environmental controller 118 may be controlled by way of a low voltage circuit that is separate from the electrical components of the power controller 38.

Preheating of the interior space 26 may be initiated prior to the power controller 38 being turned on, such that the environment within the interior space 26 is suitable for the electrical components of the control unit compartment 36 before these are operated. In this case, the heating elements 42 are controlled by the environmental controller 1 18 to increase the temperature of the interior space 26. In the embodiment illustrated in Figure 3a, two heating elements 42 are positioned in the control unit compartment 36 so as to quickly raise the temperature within the control unit compartment 36 until a temperature monitored by temperature sensor 40 exceeds a predetermined threshold level, such as 15°C, and the relative humidity recorded by the humidity sensor 116 is below a predetermined threshold level, such as 60%.

At this stage, power is supplied to the electrical components of the control unit compartment 36, and the heating elements 42 are operated to further increase the temperature within the converter cabinet 1 1 to an appropriate level. At any stage of the preheating process, if the recorded temperature exceeds a threshold level, or the relative humidity is falls below a threshold level, the heating elements 42 may be configured to be switched off.

The power converter cabinet assembly 10 described herein has a number of associated advantages, particularly in terms of maintenance and repair. Firstly, a significant benefit is that all of the air cooling equipment such as heat exchangers 88, fans 64, 74 and associated ducting is contained within the base frame 14. In some known cabinet assemblies, the base frame is simply a structural part that is designed to bear the weight of the individual cabinets or compartments that are mounted onto it, primarily for the convenience of assembling those compartments into a single assembly for installation purposes. However, in the illustrated embodiments the base frame 14 serves a useful purpose since it houses the air cooling apparatus 60. This has packaging benefits since it becomes possible to centralise the equipment required for cooling the air flow around the cabinet housing in a single area, instead of distributing fans and the like in the separate compartments of the cabinet assembly. Centralising the equipment in this way also may provide a weight and cost advantage.

Provision of a separate duct 72 for housing the external fan 74 allows for the external fan 74 to be accessed by maintenance personnel without the need for access to the base frame 14. In fact, the external fan 74 and the associated filter are each replaceable or repairable by access through the nacelle floor. The internal fan 64 is positioned so as to be accessible by way of an opening in the converter cabinet. In particular, the internal fan 64 is accessible through the control cabinet compartment 36. Maintenance of the liquid cooling apparatus, the air cooling apparatus 60 and the fans 64, 74 of the power converter cabinet assembly 10 therefore do not require access to the majority of the compartments of the main housing 12, guarding against any damage to the electrical components of the power converter 28 during repair operations.

Alternative embodiments are envisaged in which the heat exchangers 88 may be arranged in removable drawers in the base frame 14, so that the heat exchangers 88 can be withdrawn from the base frame 14 in a lateral direction.

In addition, locating all of the cooling apparatus within the base frame 14 allows for substantially all of the main housing 12 to be dedicated to the electrical components of the power converter 28, allowing for greater flexibility in the packaging arrangement of the compartments. Further, the arrangement requires only two fans 58, 65 to operate, and housing the fans 58, 65 within the base frame 14 allows for greater flexibility in the choice of fans 58, 65. The internal and external fans 58, 65 can therefore be larger, relative to existing arrangements. Advantageously, having an internal cooling loop 82 that is fluidly separate from the external cooling loop 84 allows the main housing 12 to have its own climate, which is different to the climate of the nacelle. The internal volume of the converter cabinet assembly 10, and the electrical components housed therein, is therefore isolated from the climate of the nacelle, in terms of temperature, humidity, pollution and contaminants.

In the embodiment described herein, the power converter cabinet assembly 10 may be positioned within the nacelle 6 of the wind turbine generator 2. However, it will be appreciated that the power converter cabinet assembly 10 could also be positioned at any other suitable location in or around the wind turbine generator 2, for example, within the tower 4, or positioned externally to the wind turbine generator 2, in a separate housing on the ground at the base of the tower 4, for example.

Many modifications may be made to the above examples without departing form the scope of the invention as defined in the accompanying claims.