DK180572B1

DK180572B1 - Short term power supply to a critical load of an auxiliary system

Info

Publication number: DK180572B1
Application number: DKPA201970717A
Authority: DK
Inventors: Rosenvard Paw
Original assignee: Kk Wind Solutions As
Priority date: 2019-11-22
Filing date: 2019-11-22
Publication date: 2021-08-04
Also published as: DK201970717A1

Abstract

A power supply system for an auxiliary system of a wind turbine, the power supply system comprises: one or more rectifiers, a DC bus, an energy storage, and a controller, wherein a first of the plurality of electric loads is a non-critical electric motor connected to the DC bus via a motor drive. The controller is configured for reducing a speed or torque reference to the motor drive connected to the non-critical electric motor so as to reduce the speed of the non-critical motor faster than the inertia hereof which is thereby regenerating an electric voltage and an associated electric current, the associated electric current being supplied back to the DC bus via the motor drive. Wherein a second of the plurality of electric loads is a critical electric load is configured for being at least partly powered with the associated electric current generated by the non-critical electric motor.

Description

DK 180572 B1 1

SHORT TERM POWER SUPPLY TO A CRITICAL LOAD OF AN AUXILIARY

SYSTEM Field of the invention The invention relates to a short term power supply system for an auxiliary system of a — wind turbine and to a method of establishing the short term power supply. Background of the invention

[0001] Wind turbines are today equipped with several critical and non-critical loads. In case of a fault in the main power supply to the critical loads, the critical loads are supplied from backup power systems. Such backup power systems may comprise — different kind of UPS (UPS; Uninterruptible Power Supply) solutions including different kinds of energy storage. US2017358929A1 disclose an example of a system having multiple energy generators connected to multiple energy storage. However, the minimum guaranteed transition time of some of these backup systems are not sufficiently low to comply with power supply sensitive critical loads of the wind turbines auxiliary systems.

DK 180572 B1 2 Summary of the invention

[0002] It is an object of the present invention to solve the above problem, accordingly, an exemplary embodiment relates to a power supply system for an auxiliary system of a wind turbine, the power supply system is in its first end electrically connected to a generator of the wind turbine and in its second end electrically connected to a plurality of electric loads, the power supply system comprises: one or more rectifiers, a DC bus, an energy storage, and a controller. The one or more rectifies are configured for rectifying the variable voltage from the generator and supply the rectified voltage to the DC bus. The energy storage is electrically connected to the DC bus and thereby configured for being charged and discharged via the DC bus. The plurality of electric loads is connected to the DC bus and thereby configured for being supplied from the DC bus. A first of the plurality of electric loads is a non-critical electric motor connected to the DC bus via a constant frequency output module. The controller is configured for reducing a speed or torque reference to the constant frequency output module connected to the non-critical electric motor so as to reduce the speed of the non-critical motor faster than the inertia in the non-critical electric motor which is thereby regenerating an electric voltage and an associated electric current, the associated electric current being supplied back to the DC bus via the constant frequency output module. A second of the plurality of electric — loads is a critical electric load which is configured for being at least partly powered with the associated electric current generated by the non-critical electric motor.

[0003] This is advantageous in that the non-critical load can help the energy storage supplying the critical load e.g. during peak requirement periods and thereby the capacity of the energy storage can be reduced leading to a reduce price and footprint — ofthe energy storage.

[0004] This is further advantageous in that it has the effect, that reaction time from a fault is detected to power supply changes to backup supply is reduced. This is especially true in the situation where a fault happens while the energy storage is being charged in that then the direction of current to / from the energy storage needs to be changed. During this transition period of time, the non-critical electric motor can at

DK 180572 B1 3 least partly supply the critical load, thereby keeping it alive until the energy storage is ready to supply the DC bus.

[0005] The electric connection of the first end of the power supply system to the generator of the wind turbine can be directly or indirectly. Hence, the connection can be established at any point in the electric path from the generator to the utility grid. Examples of such connection points are between the generator and rectifier (of power converter of wind turbine), in the DC link (of the power converter), between inverter and switch gear of the wind turbine, etc.

[0006] The electric loads connected to the second end of the power supply system are typically power consumers of the auxiliary system such as motors, pumps, controllers, climate control systems, etc. An example of an electric load is a fan motor used in a ventilation system other types of non-critical loads i.e. loads that can do without power for half a minute or more could be yaw motor and cooling systems. Such motor is referred to as a non-critical electric motor and is typically connected to — the DC bus via motor drive. A controller is via the motor drive able to control the operation of such motor including the speed hereof. Another example of an electric load is an electric pitch motor, wind turbine controller, generator / gear lubrication. Such pitch motor is referred to as a critical load in that in case the pitch motor is out of operation, the rotation speed of the rotor of the wind turbine may not be controllable. — Such pitch motor is also typically connected to the DC bus via a motor drive via which a controller is able to control it.

[0007] The one or more rectifies are preferably standard off the shelf components which when implemented in the power system are configured for rectifying the variable voltage from the generator and supply the rectified voltage to the DC bus and thereby to the electric loads.

[0008] According to an exemplary embodiment, the controller is a power supply system controller. Implementing an energy storage controller is advantageous in that it may control the voltage / current on the DC bus independent of the wind turbine controller and if a fault occurs preventing communication between the wind turbine

DK 180572 B1 4 controller the electric loads / drives hereof. Such fault will therefore not influence the availability of the backup power delivered from the power supply system and thereby the operation of the critical loads. In fact, an example of a critical load could be the wind turbine controller.

[0009] It should be mentioned that the controller may also be the wind turbine controller or a combination of the wind turbine controller and the energy storage controller.

[0010] According to an exemplary embodiment, the controller is reducing the speed reference or torque reference to the non-critical electric motor when a voltage measurement or a derivable hereof is outside a predetermined range of +15%, preferably £10% of the nominal voltage of the DC bus or of the nominal voltage of a utility grid connected to the wind turbine. The voltage measurement is made at the one or more rectifiers, at the DC bus or at the electric system connecting the wind turbine generator to the utility grid.

[0011] This is advantageous in that it has the effect that, in case of a power supply event such as a grid event occurs or a fault in the electric system of the wind turbine, the controller ensures that the critical loads are supplied with power. A grid event or electric fault is indicated by a change in voltage outside the above specified predetermined range. The nominal voltage depends on where it is measure, but — examples could be 230V, 400V or 690V AC or 560V DC.

[0012] A power supply event is typically the consequence of a fault in the wind turbine or within the power supply system. Such fault can be in the electric or mechanical system of the wind turbine i.e. a defect rectifier, switch gear just to mention two sources. Alternative a power supply event may be caused by manually putting the — wind turbine in off-grid or service mode.

[0013] A power supply even may be detected e.g. by a voltage sensor measuring voltage of the DC bus and which is connected to the controller. Alternatively, the wind turbine controller and the energy storage controller may communicate updated

DK 180572 B1 information of power supply faults such as voltage, current, frequency, mechanical faults, grid faults, electric faults of the wind turbine, etc.

[0014] Derivables of the voltage should mainly be understood as current or frequency, but could be other relevant electric measures.

5 [0015] According to an exemplary embodiment, the controller is configured for monitoring current on the DC bus and ramping up the voltage on the DC bus with a constant current, in case a voltage below the lower limit of the predetermined range is measured.

[0016] This is advantageous in that it has the effect, that the current will also increase — slowly compared to the situation where nominal voltage is reached as fast as possible. Hence, slowly is understood as reaching nominal voltage within 2-5 seconds from measurement of the voltage below the predetermined range.

[0017] The ramping up of the voltage can be established by controlling the speed or torque reference to the non-critical electric motor or by a sequential connection of energy storage modules of the energy storage. It should be mentioned, that it is possible also to control the voltage based on time i.e. setting a time within which a specified voltage should be reached. This is also how the speed of the non-critical electric motor is operated when operated in the regeneration mode of operation. Further, it should be mentioned that the ramping up could alternatively also be controlled according to a constant torque of a critical load in the form of a motor connected to the DC bus.

[0018] According to an exemplary embodiment, the controller periodically reduces the voltage of the DC bus. This is advantageous in that it has the effect, that in this way it can be tested if an alternative power source is ready to take over the supply of critical loads. An alternative power source could be in the form of a diesel generator, — fuel cell or the like which may take 1 or 2 minutes to start up and take over supply of critical loads.

[0019] According to an exemplary embodiment, the controller is configured for establishing a consumption of energy generated by an electric load during a grid event

DK 180572 B1 6 or fault in the electric system of the wind turbine. The consumption is established by charging of the energy storage or powering an electric load.

[0020] This is advantageous in that it has the effect, that if e.g. the wind turns the wind turbine, when the auxiliary system is powered from the energy storage, the regenerated voltage in the yaw motors can be used e.g. for charging the energy storage and not burned off in a dump load.

[0021] According to an exemplary embodiment, the critical load is powered at least partly from the non-critical electric motor or at least partly from one or more capacitors connected to the DC bus.

[0022] This is advantageous in that it has the effect, that the capacitors instantly can be used as power source for the critical load followed by the regenerating non-critical electric motor and the energy storage. Thereby (even without the capacitors), is obtained an extremely fast backup power supply system for critical loads of an auxiliary system of the wind turbine.

[0023] According to an exemplary embodiment, the critical load is powered from the non-critical electric motor in a first period of time after an unexpected change of voltage on the DC bus.

[0024] An unexpected change of voltage on the DC bus (also referred to a s power supply event) may occur as result of a fault as described above. This is possible — because the non-critical electric motor as described above in this situation is operated to regenerate voltage / current. The first period of time is typically counted in seconds and is preferably not above 5 seconds. The first period is defined by the voltage available on the DC bus, hence as long as the voltage generated by the non-critical electric motor is sufficiently high and higher than the voltage of the energy storage, — the critical load will be supplied from the non-critical electric motor. Accordingly, the duration of the first period of time is dynamic in the sense that it e.g. depends on the motor speed at the time the fault occurs.

DK 180572 B1 7

[0025] During the first period of time, the critical load may be supplied solely from the non-critical electric motor. Alternatively, the critical load may be supplied partly from the non-critical electric motor and partly from capacitors connected to the DC bus. In yet another alternative, the critical load may be supplied partly from the non- critical electric motor and / or partly from capacitors connected to the DC bus and / or partly from the energy storage or any combination hereof.

[0026] According to an exemplary embodiment, the energy storage is connected to the DC bus via a controllable bidirectional DC/DC converter or via two unidirectional DC/DC converters.

[0027] Connecting the energy storage to the DC bus via a controllable DC/DC converter or controlling switches and thereby establish current paths through one of the opposite unidirectional rectifiers is advantageous in that it has the effect, that the charge and discharge of the energy storage can be controlled by the controller. Hence, the energy storage can be controlled to either deliver or absorb an electric current from — the DC bus. Accordingly, the DC / DC converter or one of the unidirectional rectifiers can be referred to as a charger / discharger of the energy storage.

[0028] The controller determines when to charge or discharge based on measured voltage of the energy storage. Alternatively, the controller may facilitate a periodic charge / discharge of the energy modules of the energy storage to ensure that energy — modules are always ready and functional.

[0029] It should be mentioned, that the DC/DC converter could by any suitable type including a multiple DC/DC converter.

[0030] According to an exemplary embodiment, the energy storage comprises at least one string comprising a plurality energy modules, wherein the energy storage controller is configured for controlling a current path including and / or excluding at least one of the plurality of energy modules wherein the current path is controlled by a plurality of switches configured to include or exclude the individual energy modules.

DK 180572 B1 8

[0031] This is advantageous in that it has the effect, that the voltage level of the energy storage can be controlled based on the number of battery modules which is included in the current path.

[0032] Moreover, the invention relates to a method of establishing a power supply to an electric load of an auxiliary system of a wind turbine, the auxiliary system comprises non-critical loads and critical loads electrically connected to a DC bus, the method comprising the steps of: via a controller detecting a power supply fault to at least one critical load of the auxiliary system, and via the controller change mode of operation of at least one non-critical load from a normal mode of operation to a regeneration mode of operation. Upon detection of the power supply fault, the at least one critical load is first supplied with power, via the DC bus, established by the non- critical load operated in the regeneration mode of operation, and subsequently supplied with power from an energy storage electrically connected to the DC bus.

[0033] This is advantageous in that it has the effect, that immediately after a fault leading to an interruption of the power supply to a critical load is detected, the critical load is supplied with power, for a short period of time, generated by the non-critical load operated in a regeneration mode of operation. In this way time is gained allowing the controller to wake up the energy storage, change mode of operation of the energy storage (e.g. from charge mode to discharge mode), etc.

[0034] Immediately should here be understood as within a first time period of time i.e. the time it takes the non-critical load e.g. in the form of an electric motor to react on a reduced speed reference, making the electric motor reduce speed faster than the inertia comprised by the electric motor and thereby regenerate an electric voltage and an associated current which is then feed back to the DC bus and usable by the critical load.

[0035] Short period of time should here be understood as the limited first period of time the non-critical load can be operated in the regeneration mode of operation i.e. establishing a voltage and delivering an associated current back to the DC bus. This period of time is determined e.g. by the size of the non-critical load and thereby e.g.

DK 180572 B1 9 the inertia comprised by a non-critical load in the form of an electric motor. Typically, this first period of time is between 0,5 and 2 second (but could be higher up to 5 or 8 seconds depending on the situation) and after this short period of time, if the fault still occurs, the critical load is supplied with power from the energy storage electrically — connected to the DC bus.

[0036] The controller is preferably a power supply controller communicating with the energy storage / energy storage charger and the non-critical load / driver hereof. Further it may communicate with the critical load and / or a wind turbine controller. The detection of a fault in the power supply may not necessarily be made by the power — system controller. It can be made by sensors connected to other controllers such as the wind turbine controller, such controllers may then communicate relevant information to the power system controller. Further, the change of mode of operation of the non- critical load may not necessarily be made by the power system controller. It can be made by e.g. the wind turbine controller.

[0037] It should be mentioned, that capacitors may also be connected to the DC bus and assist the non-critical load operated in the regeneration mode in suppling power to the critical load in the time just after detection of a power supply fault.

[0038] When the non-critical load is no longer able to (fully) supply the critical load, the critical load is supplied from the energy storage. The critical load is supplied from — the energy storage as long as necessary i.e. as long as the power supply fault occurs or as long as the there is sufficient energy in the energy storage. Hence the critical load may be supplied both from the non-critical load and from the energy storage. Further, the non-critical load may be used to absorb high peak voltages.

[0039] According to an exemplary embodiment, the non-critical electric load is a non-critical electric motor and wherein the regenerative mode of operation is established by the controller by reducing a speed or torque reference to a constant frequency output module connecting the non-critical electric motor to the DC bus.

DK 180572 B1 10 The drawings

[0040] For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts: Figure 1 illustrates a schematic view of an embodiment of the invention where a critical load is supplied by a non-critical load and by an energy storage, and Figure 2 illustrates a schematic view of an alternative embodiment of the invention.

Detailed description

[0041] Figure I illustrates a schematic view of an embodiment of the invention where a wind turbine 3 is represented by the generator 4. The wind turbine 3 is not illustrated in figure 1 but could be any type of wind turbine 3. Such wind turbine 3 comprises a tower, a nacelle, a hub and two or more blades. The blades of the wind turbine are rotatable mounted on the hub, together with which they are referred to as the rotor.

The area covered by the blades when the rotor rotates is referred to as rotor plane. The rotation of a blade along its longitudinal axial is referred to as pitch.

[0042] The wind turbine is controlled by a control system comprising a wind turbine — controller 9, sub controllers for controlling different parts of the wind turbine and communication lines 16. The wind turbine controller 9 is preferably communicating with external controllers and operators. Hence it is possible to update, correct, check status, etc. the wind turbine controller and software thereon.

[0043] The wind turbine 3 generates electric power from the wind which makes the — rotor rotate. The rotor is coupled to a generator 4 which generates the electric power.

The power generated from the generator 4 is in variable speed wind turbines shaped by a converter to comply with grid codes of the local utility grid. Some wind turbines

DK 180572 B1 11 such as stall controlled wind turbines, have no converter and is coupled directly to the utility grid. The power supply system 1 of the present invention is suitable on any types of wind turbines and can be connected to the electric system of the wind turbine between the generator 4 and the utility grid. In an embodiment, the connection is established as close to the generator 4 as possible to avoid converter faults affecting the power supply to the auxiliary system 2. Further it should be mentioned that the generator 4 in some embodiments, may be grid connected.

[0044] The ways of producing energy from a wind turbine 3 and the components such as generator and converter used hereto is not illustrated nor explained further in that it is how wind turbines I are operating and thereby known by the skilled person.

[0045] Figure 1 illustrates a power supply system 1 according to an embodiment of the invention. A first end of the power supply system la is connected to a generator 4 of the wind turbine 3. Located in the first end of the power supply system la is a plurality of paralleled rectifiers 6. The voltage and associated current generated by the — generator 4 is variable AC voltage and hence the rectifiers 6 are rectifying this AC voltage to a DC voltage. The DC voltage is then available on the DC bus 7 connected to each of the rectifiers 6. The second end of the power supply system 1b is connected to one or more electric loads 5 which are supplied with the rectified DC voltage / current on the DC bus. The voltage of the DC bus may in an embodiment vary between — 400-800V.

[0046] The rectifiers 6 are preferably standard of the shelf rectifiers connected in parallel. This means that only the number of rectifiers needed for rectifying the AC voltage generated by the generator 4 is used. This voltage is typically varying quite a lot, however this challenge is handled by the paralleled rectifiers. In an embodiment, together the capacity of the number of paralleled rectifiers sums up at least to the nominal capacity of the auxiliary system. Hence, the power supply system can be said to be adapted to the individual wind turbine (loads hereof) and hence not necessarily usable in other types of wind turbines than the one it is designed for.

DK 180572 B1 12

[0047] The DC bus 7 is connecting the output of the rectifiers 6 to the electric loads 5, the energy storage 8 and capacitors 11. The DC bus is a standard feature of an electrical system of a wind turbine and is therefore not explained in further details.

[0048] The electric loads 5 are those loads which must be running for operating the — wind turbine 3 in the long run. Accordingly, this therefore relates to climate control including heating, cooling, ventilation, drying, etc., motors for actuating pitch, yaw, ventilation, lubrication, etc., controllers for controlling electric and mechanical features of the wind turbine, light, service lift, etc. Critical electric loads Sb are those which needs to be running to ensure safety, restart after stand still, positioning of rotor — and blades during stand still and similar. These critical loads need to be prioritised in case of lack of power over non-critical loads. Non-critical loads may include various motors and auxiliary systems which is not used during operation of the wind turbine or the operation of which can be paused during operation of the wind turbine. This includes motors for ventilation, for service lifts, some heating systems during summer time, some cooling systems during winter time, etc.

[0049] The power supply system is preferably controlled by a power supply controller 9a. However, the functionalities could also be implemented in the wind turbine controller 9b. The main functionality of the power supply controller 9a is to monitor and control voltage level on the DC bus 7. This is done by voltage and / or — current sensors (not illustrated) and based on these measurements control non-critical loads 5a to enter a regeneration mode of operation or enable power supply from the energy storage 8. Further, the power supply controller 9a may initiate periodical charge and discharge of energy modules 13 of the energy storage 8.

[0050] The power supply controller 9a is programmable to react on voltage levels (when voltage levels are mentioned this includes derivables hereof such as frequency, current, etc.) that is a certain percentage off a desired voltage level. Hence, if the desired voltage level on the AC side of the rectifiers 6 is a nominal voltage of 400V, a range around 400V of e.g. +10% could be considered as normal operation, whereas voltages outside this range i.e. below 360V or above 440V is considered a power supply event. The power supply event may occur from e.g. a grid event or a from a

DK 180572 B1 13 mechanical or electric fault of the wind turbine. The range of +10% is only an example and could be +5% to +15% depending on under what ranges the electric loads supplied can operate. The lower deviation may also be higher than the upper deviation and vice versa.

[0051] In an embodiment, the voltage is measured at the rectifiers to be able to monitor operation when the power supply system is connected to the utility grid via the wind turbine electric system. In addition, the voltage is also measured at the DC bus to be able to regulate the voltage hereof i.e. react if grid voltage disappears or is outside the defined range.

[0052] Ina situation where the grid voltage is below e.g. 10% of its nominal (desired) value, the power supply controller 9a take actions that leads to an increase of the DC voltage of the DC bus. It is preferred that the controller 9 is regulating the DC voltage up to desired level without generating a high current while doing so. This can be avoided by slowly increasing the DC bus voltage e.g. controlling the voltage increase according to a constant current or torque.

[0053] An additional feature is that it is possible, when the critical loads are supplied from the energy storage, to reduce the voltage of the DC bus to see if auxiliary power supplies such as diesel generators or fuel cell generators are ready to take over the power supply.

[0054] In an embodiment, if the voltage at the generator is 400VAC, the rectified voltage at the DC bus is S60VDC which is the supply voltage to the electric loads 5. If a fault happens at the generator 4, wind turbine 3, rectifiers 6, etc. the 400VAC / 560VDC may completely or partly disappear. In this situation, the controller 9 e.g. reduces the speed (or torque) reference to a non-critical electric motor load faster than — the inertia of the motor. This means that the non-critical electric motor is operated in the regenerating mode of operation and a voltage is therefore generated. This voltage and associated current is feed back to the DC bus where other loads can use it as supply.

DK 180572 B1 14

[0055] The steeper reduction curve (of speed or torque) the drive is controlled to ramp down with the higher current is established in a shorter time and vice versa. It is preferred to use e.g. a fan motor compared to a pump motor in that the resistance from the liquid fluid of the pump will help the inertia brake the motor leading to a reduce regeneration. The motor drives may be controlled by parameter lists so that if e.g. voltage is in one range it is one parameter list that is used to control the motor, if the voltage change the parameter list change. The parameter list or change between parameter lists may be controlled by the power supply controller 9a. Alternatively, the wind turbine controller 9b can control the parameter lists.

[0056] It should be mentioned that the motor drive could be any type of constant output frequency modules.

[0057] In the above example, the inertia of the non-critical electric motor may start producing S80VDC which is enough to supply a critical load for a short period of time. However, as the inertia is converted to electric energy the produced voltage decreases and reaches e.g. SOOVDC. This reduction may happen during a period of time which typically is below 5 seconds and typically between 0,5 second and 2 seconds, however it depends on size of motor and motor speed. Thereby, the energy storage has 0,5 or more seconds to cut in which is sufficiently in that transition time in some backup systems may be down to even 20 milliseconds. However, such systems worst case scenarios typically will have longer transition time, during such time the power supply system of the present invention can act as backup power supply system. If the energy storage 8 in the above example is able to deliver S00VDC, the critical load may at this point in time be supplied from both the non-critical electric motor and from the energy storage (or alternating therebetween in dependency of voltages available or priority in control). Finally, when the voltage produced by the non-critical electric motor is too low (compared to the need of the critical load), the critical load is supplied solely from the energy storage.

[0058] It should be mentioned that, other interim energy storages such as capacitors on the DC bus could be used in combination with the non-critical electric motor and the energy storage.

DK 180572 B1 15

[0059] In figure 1, the supply of the critical load 5b first from the generator 4 and then subsequently from the non-critical electric motor 5a is illustrated by arrows 17a, 18a. The first supply path is denoted 17a (grid connection mode of operation) and the second supply is denoted 18a (backup mode of operation). It should be noted that the critical load 5b subsequently may be suppled from the energy storage 8 illustrated by arrow 18b.

[0060] It should be noted, that even though it is stated that only critical loads are powered from the regenerated voltage of the non-critical loads, then it is also possible to supply other non-critical loads from such regenerated voltage or from the energy — storage. Which electric loads 5 that are to be powered during a backup power mode of operation may be prioritised by the controller 9 i.e. programmed into a program code executed by the controller.

[0061] The embodiment illustrated on figure 2 illustrates a few additional elements compared to the embodiment illustrated on figure 1. One of these elements are an — energy storage charger 12. The energy storage charger 12 may be implemented as a single / multiple DC / DC converter or as two unidirectional DC converters (not illustrated). The battery charger 12 is preferably controllable by the power supply system controller 9a so as to facilitate charging of the energy storage 8. A non- illustrated additional element is a constant frequency output module which can be installed between the electric load 5b and the DC bus7. As explained, the constant frequency output module is typically a motor drive but could also be implemented as an UPS (UPS; uninterruptible power supply) or a solid state device.

[0062] In the situation where the energy storage 8 is being charged and a power supply fault such as a grid event occurs it may take a period of time in the range of a — couple of milliseconds (e.g. from 10 milliseconds) to 2 seconds to change mode of operation from charge to discharge. During this period of time, the critical load can be supplied from the non-critical load as explained above.

[0063] Figure 2 further illustrates DC bus capacitors 11 which during normal operation are used to smoothen the voltage of the DC bus. However, in case of a fault

DK 180572 B1 16 as described above, the DC bus capacitors can, as the non-critical load, be used as short term supply to a critical load.

[0064] In an embodiment, the energy storage 8 comprises a plurality of energy storage modules 13 which may comprise one or more storage element such as batteries, capacitors, etc. By controlling which and how many of these modules that is connected to the DC bus when the DC bus is supplied from the energy storage, the voltage of the DC bus can be controlled. This control is in an embodiment of the invention facilitated by a separate energy storage controller (9c).

[0065] The controllers 9 (power supply controller 9a, wind turbine controller 9b and — energy storage controller 9c) may share functionalities and therefore one may replace the other. The controllers 9 may communicate with each other and with DC/DC converter 12, motor drive 10, etc. via communication lines 16.

[0066] As illustrated, the energy storage 8 comprises a plurality of energy modules 13 each comprising one or more storage elements preferably in the form of batteries — or capacitors. Each energy module 13 is individually controlled by a switching arrangement 15. In the illustrated embodiment, one energy module 13 is by-passed by the switching arrangement 15. The switching arrangement can be implemented as an h-bridge of semiconductors switches such as IGBTs or MOSFETs. The switching modules 15 and thereby the charging / discharging of the energy modules 13 is controlled by an energy storage controller 9c, which is communicating with the power supply system 9a.

[0067] From the above it is hereby clear, that the present invention relates to a power supply system that not only is able to supply critical electric loads from an energy storage but also from a non-critical electric motor. Hence, with reference to figure 1 and 2, the arrows denoted 17 refers to power supply path of electric loads during normal grid mode of operation where as the arrows denoted 18 refers to power supply path of electric loads during backup mode of operation.

[0068] The regeneration mode of operation of a non-critical electric motor is established by controlling the speed or torque reference to the motor drive / constant

DK 180572 B1 17 frequency module of the non-critical electric motor. An example of a critical load is the wind turbine controller 9c and pitch motor and an example of a non-critical load is the fan motor for ventilation system of the nacelle or generator.

[0069] In a simplified embodiment, a 22kW fan motor is considered as a non-critical electric motor connected to the DC bus via a 22kW drive. A 10kW motor considered as a critical load is also connected to the DC bus. The 10kW motor can be partly supplied form the 22kW motor and partly from the energy storage. Hence, the capacity of the energy storage can be reduced in that the 10kW motor is partly supplied from the 22kW motor (it does not have to comply with high peak values).

[0070] In an embodiment, the power supply system 1 comprises multiply AC-DC converters/rectifiers 6 in parallel that charges the common DC-bus 7, provided with Capacitors, Batteries, or other storage elements for short and long time storage e.g. flywheels, air pressure accumulators or heat exchangers, e.g. in combination with excess power storage such as hydrogen or methanol production units. The DC-bus 7 — can thus be charges or filled up with different power sources, aux grid, solid/gas fuel generator, sterling motors, etc. The power output from the DC-bus can be used directly, or with inverters/converters can supply e.g. variable frequency, fixed voltage fixed frequency, variable frequency, variable voltage, variable voltage (DC) and fixed voltage (DC) to electric loads of the auxiliary system of the wind turbine.

DK 180572 B1 18 List

1. Power supply system

2. Auxiliary system

3. Wind turbine

4. Wind turbine generator

5. Electric load a. Non-critical load b. Critical load

6. Rectifiers

7. DC bus

8. Energy storage

9. Controller a. Power storage controller b. Energy storage controller c. Wind turbine controller

10. Motor drive / constant frequency module

11. Capacitors

12. DC/DC converter

13. Energy modules

14.

15. Switch

16. Communication lines

17. Power supply path during grid connection mode of operation

18. Power supply path during backup mode of operation

Claims

DK 180572 B1 1 Patentkrav

Power supply system (1) for an auxiliary system (2) of a wind turbine (3), which power supply system (1) is electrically connected at its first end (1a) to a generator (4) of the wind turbine (3) and at its second end (1b) is electrically connected to a - plurality of electrical loads (5), the power supply system (1) comprising: e one or more rectifiers (6), e a DC bus (7), e ethene energy storage (8), and e a control unit (9), wherein the one or more rectifiers (6) are configured to rectify the variable voltage from the generator (4) and supply the rectified voltage to the DC bus (7), where the energy storage (8) is electrically connected with the DC bus (7) and thus configured to be charged and discharged via the DC bus (7), the plurality of electrical loads (5) being connected to the DC bus (7) and - thus configured to be supplied from The DC bus (7), wherein a first of the plurality of electrical loads (5a) is a non-critical electric motor (5a) connected to d The DC bus (7) via a constant frequency output module (10), the control unit (9) is configured to reduce a speed or torque reference to the constant frequency output module (10) connected to the non-critical electric motor ( 5a), so as to reduce the speed of the non-critical motor (5a) faster than the inertia of the non-critical electric motor (5a), which thereby regenerates an electric voltage and an associated electric current, the associated electric current being supplied back to The DC bus (7) via the constant frequency output module (10),

DK 180572 B1 2 where the power supply system is characterized in that a transition time is defined as a period of time between detecting a power supply fault and establishing a backup supply from the energy storage (8), where another of the plurality of electrical loads (5b) is a critical electrical - load configured to be powered by detecting a power supply failure: first with the associated electric current generated by the non-critical electric motor (52), thereby reducing the transition time, and subsequently with current from the energy storage (8); , which is electrically connected to the DC bus (7).

The power supply system (1) according to claim 1, wherein the control unit (9) is a power supply system control unit (9a).

A power supply system (1) according to claim 1 or 2, wherein the control unit (9) reduces the velocity reference or the torque reference to the non-critical electric motor (5a) when a voltage measurement or a derivative thereof is outside a predetermined range of +15%, preferably +10% of the nominal voltage of the DC bus (7) or of the nominal voltage of a supply network connected to the wind turbine (3), where the voltage measurement is made at one or more rectifiers (6), at the DC bus (7) or by the electrical system connecting the wind turbine generator (4) to the supply network.

A power supply system (1) according to any one of the preceding claims, wherein the control unit (9) is configured to monitor current on the DC bus (7) and increase the voltage on the DC bus (7) with a constant current, if a voltage below the lower limit of the predetermined range is measured.

A power supply system (1) according to any one of the preceding claims, wherein the control unit (9) periodically reduces the voltage of the DC bus (7).

DK 180572 B1 3

A power supply system (1) according to any one of the preceding claims, wherein the control unit (9) is configured to establish a consumption of energy generated by an electrical load (5) during a supply network event or failure of the wind turbine electrical system, Where the consumption is established by charging the energy storage (8) or supplying power to an electrical load (5).

A power supply system (1) according to any one of the preceding claims, wherein the critical load (5b) is supplied at least in part from the non-critical electric motor (5a) or at least in part from one or more capacitors (11 ), - connected to the DC bus.

A power supply system (1) according to any one of the preceding claims, wherein the critical load (5b) is supplied with power from the non-critical electric motor (5a) for a first period of time after an unexpected voltage change on the DC bus (7).

Power supply system (1) according to any one of the preceding claims, wherein - the energy storage (8) is connected to the DC bus (7) via a controllable two-way DC / DC converter (12) or via two one-way DC / DC converters.

A power supply system (1) according to any one of the preceding claims, wherein the energy storage (8) comprises at least one string comprising a plurality of energy modules (13), wherein the energy storage control unit (9a) is configured to control a> current path, including and / or excluding at least one of the plurality of energy modules (13), the current path being controlled by a plurality of switches (15) configured to include or exclude the individual energy modules (13).

Method for establishing a power supply for an electrical load (5) of an auxiliary system (2) of a wind turbine (3), the auxiliary system (2) comprising non-critical loads (5a) and critical loads (5b), which is electrically connected to a DC bus (7), which method comprises the following steps: e detecting, via a control unit (9), a power supply fault to at least one critical load (5b) of the auxiliary system (2), and

DK 180572 B1 4 e change, via the control unit (9), of the operating mode of at least one non-critical load (5a) from a normal operating mode to a regeneration operating mode, where a transition time defines a time period between detecting a power supply fault and establishing a a backup supply from an energy storage (8), and - where, upon detection of the power supply fault, during the transition time, the at least one critical load (5b) is first supplied with power via the DC bus (7), established by means of the non-critical load; (5a) operated in the regeneration operating mode and subsequently supplied with power from the energy storage (8) electrically connected to the DC bus (7).

A method according to claim 11, wherein the non-critical electrical load (5a) is a non-critical electric motor, and wherein the regeneration operating mode is established by the control unit (9) by reducing a speed or torque reference to a constant frequency output module (10). , which connects the non-critical electric motor to the DC bus (7).