Low-wind ride-through of a wind turbine

Abstract

A method of controlling a wind turbine is provided including a generator system, an energy storage system and auxiliary equipment, the method including, in particular during a low wind condition: controlling the generator system in order to provide power from the generator system to the auxiliary equipment, in particular such that a rotor speed does not decrease; controlling the energy storage system in order to provide power from the energy storage system to the auxiliary equipment, if required to meet a power requirement of the auxiliary equipment; in particular keeping the wind turbine in operation.

Claims

1. A method of controlling a wind turbine comprising a generator system, an energy storage system and auxiliary equipment, the method comprising, during a low-wind condition: controlling the generator system in order to provide power from the generator system to the auxiliary equipment, such that a rotor speed does not decrease; and controlling the energy storage system in order to provide power from the energy storage system to the auxiliary equipment, if required to meet a power requirement of the auxiliary equipment; the controlling the generator system and controlling the energy storage system further comprising: determining a first amount of electrical power the generator system is capable of delivering; if the first amount of power is smaller than a third amount of power needed by the auxiliary equipment: providing substantially the first amount of power from the generator system to the auxiliary equipment; determining a second amount of power such that the sum of the first amount and the second amount of power substantially equals the third amount of power; providing the second amount of power from the energy storage system to the auxiliary equipment, wherein the first amount of power is determined to be limited such that the rotor speed of the rotor does not decrease substantially, when the first amount is actually extracted from the generator system, wherein the low wind condition is when the rotational speed of the rotor deviates less than 20% from a minimum rotational speed.

2. The method according to claim 1, wherein the first amount of electrical power is determined depending on and/or based on an actual rotor speed.

3. The method according to claim 1, wherein at least one of the following applies: the first amount, the second amount and the third amount are subject to change over time depending on external and/or internal conditions and/or operating parameters; the wind turbine is not shut-down unless the first amount is lower than a minimum active power threshold or equal to or lower than zero.

4. The method according to claim 1, further comprising, if the first amount of power is equal to or greater than the third amount of power: providing the third amount of power from the generator system to the auxiliary equipment; and/or providing no power from the energy storage system to the auxiliary equipment.

5. The method according to claim 1, wherein, if the first amount of power is smaller than a minimum active power threshold or is equal to or lower than zero, for more than a predetermined time duration, the method further comprises at least one of: shutting down the wind turbine; disconnecting the wind turbine from the utility grid; providing no power from the generator system to the auxiliary equipment; providing the third amount of power from the energy storage system to the auxiliary equipment, wherein the minimum active power threshold is substantially zero.

6. The method according to claim 5, wherein shutting down comprises at least one of: decreasing a rotational speed to zero; adjusting the pitch angles to a minimal lift position, feather position; disconnecting the auxiliary equipment from the utility grid; disconnecting the generator system from the utility grid; disconnecting the energy storage system from the utility grid; disconnecting the wind turbine from the utility grid.

7. The method according to claim 1, wherein at least one of the following applies: the energy storage system is connectable or connected to the generator system, via an auxiliary circuit breaker; the wind turbine and/or the auxiliary equipment is connected or disconnected and/or connectable or disconnectable from a utility grid.

8. The method according to claim 1, wherein the generator system includes, connected in the listed order, at least one of: a generator, permanent magnet synchronous generator; a converter; a reactor; a filter.

9. The method according to claim 1, wherein the low wind condition further includes at least one of: a wind speed deviates less than 20% or 10% from a minimum wind speed at which the wind turbine is still operable to produce power; the rotational speed of the rotor deviates less than 10% from the minimum rotational speed; at least one pitch angle is set for optimal power extraction from the wind.

10. The method according to claim 1, wherein at least one of the following applies: the auxiliary equipment is connectable or connected to the energy storage system; the auxiliary equipment is connectable or connected to the generator system via the energy storage system and further via a circuit breaker; and/or the auxiliary equipment is connectable or connected to the generator system not via the energy storage system and further via a circuit breaker.

11. The method according to claim 1, wherein the energy storage system comprises a DC energy storage and at least one DC-AC converter, wherein controlling the energy storage system comprises controlling the DC-AC converter, wherein the energy storage system comprises at least one of: a battery energy storage system; a hydrogen electrolysis system; a fuel cell system; a flywheel; a Diesel and/or petrol driven generator.

12. The method according to claim 1, wherein the auxiliary equipment comprises at least one of; a wind turbine auxiliary component; a pump; a fan; a motor; a yaw actuator for turning a rotor axis; a pitch actuator for a wind turbine blade; a cooling system component; a heater system component; an illumination system; a light component; a control system; a communication system.

13. The method of controlling a wind turbine of claim 1, wherein the step of controlling the energy storage system further comprising; keeping the wind turbine in operation; and wherein the minimum rotational speed, is a low-wind cut-out rotational speed, at which the wind turbine is still operable to produce power.

14. An arrangement for controlling a wind turbine comprising a generator system, an energy storage system and auxiliary equipment, during a low wind condition, the arrangement being configured: to control the generator system in order to provide power from the generator system to the auxiliary equipment, such that a rotor speed does not decrease; to control the energy storage system in order to provide power from the energy storage system to the auxiliary equipment, if required to meet a power requirement of the auxiliary equipment; to determine a first amount of electrical power the generator system is capable of delivering; if the first amount of power is smaller than a third amount of power needed by the auxiliary equipment: to provide substantially the first amount of power from the generator system to the auxiliary equipment; to determine a second amount of power such that the sum of the first amount and the second amount of power substantially equals the third amount of power; to provide the second amount of power from the energy storage system to the auxiliary equipment, wherein the first amount of power is determined to be limited such that the rotor speed of the rotor does not decrease substantially, when the first amount is actually extracted from the generator system, wherein the low wind condition is wherein the rotational speed of the rotor deviates less than 20% from a minimum rotational speed.

15. The method of controlling a wind turbine of claim 14, wherein the control of the energy storage system further comprises; to keep the wind turbine in operation; and wherein the minimum rotational speed, is a low-wind cut-out rotational speed, at which the wind turbine is still operable to produce power.

16. A wind turbine, comprising: a generator system; an energy storage system; auxiliary equipment; and an arrangement according to claim 14.

Description

BRIEF DESCRIPTION

(1) Some of the embodiments will be described in detail, with references to the following Figures, wherein like designations denote like members, wherein:

(2) FIG. 1 schematically illustrates a wind turbine according to an embodiment of the present invention;

(3) FIG. 2 schematically illustrates a wind turbine according to another embodiment of the present invention;

(4) FIG. 3 illustrates power curves for explaining embodiments of the present invention;

(5) FIG. 4 schematically illustrates a scheme of a method of controlling a wind turbine according to an embodiment of the present invention; and

(6) FIG. 5 illustrates a conventional control scheme.

DETAILED DESCRIPTION

(7) The wind turbine 100 schematically illustrated in FIG. 1, according to an embodiment of the present invention, comprises a generator system 101, an energy storage system 102 and auxiliary equipment 103. Furthermore, the wind turbine 100 comprises an arrangement 105 for controlling a wind turbine according to an embodiment of the present invention.

(8) The wind turbine 100 further comprises a rotor 120 which is mechanically coupled to the generator 115. At the rotor 120 plural rotor blades 121 are mounted. Wind 122 impacts on the rotor blades 121 and causes the rotor 120 to rotate.

(9) The wind turbine 100 comprises a main circuit breaker 112 which connects the generator system 101 via a reactor 113 and a harmonics filter 104 to a wind turbine transformer 105a. The transformer 105a transforms the voltage output by the generator system 101 to a higher voltage and supplies the high-voltage AC power stream to the utility grid 110. The embodiment 100 of FIG. 1 comprises a further circuit breaker 117 (and bypass breaker 117a) between the energy storage system 102 and a node 118 which node 118 is between the main circuit breaker 112 and the wind turbine transformer 105a. The generator system 101 comprises a circuit breaker 119 between the generator 115 and the converter 116.

(10) The generator system 101 comprises a generator 115 and an AC/DC, DC/AC converter 116. The reactor 113 and the harmonics filter, are optional components and may further be comprised within the generator system 101.

(11) The arrangement 105 is adapted to control the generator system 101, in particular by providing a control signal cs1 to the generator system 101, in order to provide power P1 from the generator system 101 to the auxiliary equipment 103. The arrangement 105 is further configured to control the energy storage system 102, in particular by supplying a control signal cs2, in order to provide power P2 from the energy storage system 102 to the auxiliary equipment 103, if required to meet a power requirement, such as P3, of the auxiliary equipment 103.

(12) The auxiliary equipment 103 may for example comprise auxiliary motors, controllers, etc. which may for example be essential for operating the wind turbine. Examples have been mentioned above.

(13) The energy storage system 102 comprises a DC energy storage 106, an AC/DC converter 107 and/or a DC/AC converter 108, both converters 107, 108 being connected with their corresponding DC components to the energy storage 106. The AC/DC converter 107 is configured to convert an AC power stream, for example received from the generator system 101 or the utility grid 110 to a DC energy stream or power which is then supplied to the DC energy storage 106 for charging. The DC/AC converter 108 comprised in the energy storage system 102 is configured to convert the DC power received from the DC energy storage 106 to an AC power which can then be supplied to the auxiliary equipment 103.

(14) The auxiliary equipment 103 is connectable, in particular by closing an auxiliary circuit breaker 111 (and breaker 117) to the generator system 101 via the energy storage system 102. Thus, when the auxiliary system 103 receives also power, such as P1, from the generator system 101, the power P1 flows through the energy storage system 102 and is provided or supplied additionally to the power P2 from the energy storage system 102 to the auxiliary equipment 103.

(15) FIG. 2 schematically illustrates a wind turbine 200 according to another embodiment of the present invention. The wind turbine 200 is similar to the wind turbine 100 illustrated in FIG. 1. Therein, similar or same components or structures as in FIG. 1, are indicated with reference signs differing only in the first digit. A description of one component not explicitly explained with reference to a particular figure may be taken from the description of this corresponding element in another figure or embodiment.

(16) As a difference to the embodiment 100 of the wind turbine illustrated in FIG. 1, the wind turbine 200 has the auxiliary equipment 203 connectable or connected to the generator system 201 not via the energy storage system 102.

(17) FIG. 3 illustrates in a graph having an abscissa indicating the rotational speed of the rotor 120 of the wind turbine and having an ordinate P indicating the power output of the generator system, such as generator system 101 or 201 illustrated in FIG. 1 or 2.

(18) The curve denoted by P1 presents a first amount of electrical power the generator system is capable of delivering, in particular without the rotational speed to decrease. According to an embodiment of the present invention, the first amount of power P1 is determined for example depending or based on measurements or estimations or simulation of one or more operational parameters, such as current, voltage, rotational speed, frequency of the power stream or based on an actual power measurement. The curve P1 is the amount of power derived by subtracting a constant amount P3 from the power curve P1. Thereby, the power P3 may represent a third amount of power which is needed by auxiliary equipment, such as auxiliary equipment 103 or 203 illustrated in FIGS. 1 and 2, respectively. In the illustrated embodiment, the third amount P3 has been set to a fixed predetermined amount of power. In other embodiments, the third amount of power P3 may be subject to change in dependence on the actual requirements of the auxiliary equipment.

(19) In the rotational speed regime 323 the first amount of power P1 is larger than the third amount of power P3. If in the rotational regime 323, the auxiliary equipment is exclusively supplied the third amount of power from the generator system. Further no power from the energy storage system is supplied to the auxiliary equipment.

(20) In the rotational speed regime 324, the first amount of power P1 is equal or smaller than the third amount of power P3. In this rotational speed regime 324, substantially the first amount of power is provided from the generator system to the auxiliary equipment (see the curve denoted P1 within the regime 324 in FIG. 3). According to an embodiment of the present invention, in this rotational speed regime 324 a second amount P2 of power is determined such that the second amount of power P2 summed with the first amount of power P1 equals substantially to the third amount of power P3. This is illustrated as a curve denoted P2 in FIG. 3 in the rotational speed regime 324. The second amount of power P2 is then provided from the energy storage system, such as energy storage system 102 or 202 illustrated in FIG. 1 or 2, respectively, to the auxiliary equipment.

(21) As a result, the wind turbine can still be operated within the rotational speed regime 324 up to or down to a cut-out rotational speed labelled as 325. Conventionally, the wind turbine is shut-down when the rotational speed is below a conventional cut-out rotational speed 326.

(22) The first amount of power P1 illustrated in FIG. 3 is limited such that the rotor speed does not decrease substantially when the first amount of power is actually extracted from the generator system and provided to the auxiliary equipment.

(23) The power labelled with reference sign 327 in FIG. 3 may correspond to a minimum active power threshold which may either be larger than zero or may substantially be zero.

(24) In the rotational speed regime 328 being lower than the cut-out rotational speed 325, the auxiliary equipment is exclusively supplied with electric energy from the energy storage system. In this regime or even below the cut-out rotational speed value 325 the wind turbine may be shut-down.

(25) FIG. 4 illustrates a method scheme 430 according to an embodiment of the present invention of controlling a wind turbine. In embodiments, the method starts at a method step 431. In a method step 432 the auxiliary equipment is supplied with power from the wind turbine, in particular the generator system, or the utility grid. In a decision element 433 it is evaluated whether the active power is smaller than the auxiliary power consumption. Thereby, the active power is in particular the total power that may be extracted from the generator as a function of the wind turbine rotor speed, minus electrical losses and losses associated with power conversion, thereby enabling that the rotational speed of the rotor stays unchanged.

(26) If the evaluation in decision element 433 evaluates as true, it is branched to the method step 434. In method step 434 the power is supplied to the auxiliary equipment from the energy storage system in combination with the amount of available active power, i.e., the active power, which is available from the generator system, in particular without reducing the rotational speed of the rotor.

(27) In a decision element 435 it is evaluated whether the active power (in particular which is then still available from the generator system even when supplying the available active power to the auxiliary system) is smaller than a minimum active power threshold. The minimum active power threshold may be substantially zero. If the evaluation in decision element 435 amounts to true, the wind turbine is shut-down in method step 436.

(28) In a decision element 437 it is evaluated whether the wind speed has increased to be sufficient for re-start. If this is evaluated as true, the wind turbine is re-started in method step 438.

(29) If the evaluation in decision element 433 evaluates as false, it is branched in a loop and it is returned to method step 432, wherein the auxiliary equipment is supplied with electrical energy by the wind turbine or the utility grid.

(30) If the evaluation of decision element 435 evaluates as false, it is looped back to the decision element 433.

(31) The minimum active power threshold may be a value close to or similar to zero kW. So, for example in a case where the auxiliary consumption is steady at a fixed value such as 40 kW, then when active power is less than 40 kw but greater than zero kW, the energy storage system is supplementing the supply of power to the auxiliaries and the turbine stays in operation. If the active power drops to zero kW, then the turbine would finally shut-down. It is noted that the active power may the power after internal transmission/conversion losses, for example, at the low-voltage side of 105a in FIG. 1 or 205a in FIG. 2.

(32) FIG. 5 illustrates a conventional method scheme 440. In a method step 441 the method is started. In a step 442 auxiliary systems are supplied by the wind turbine or the grid. In a decision element 443 it is evaluated whether the active power available from the generator system is smaller than the auxiliary power consumption. If this evaluation results in true, the turbine is shut-down in method step 444. If the evaluation in decision element 443 evaluates as false, it is looped back to the method step 442. When it is determined in decision element 445 that the wind speed increased for sufficient wind speed to re-start, the turbine is re-started in method step 446.

(33) The following features may be comprised in embodiments of the present invention, to which however embodiments of the invention are not restricted:

(34) At low wind speeds there may only be a small amount of available power which can be extracted from the generator without causing a deceleration of the rotor. According to an embodiment of the present invention, a control function limits the power that is extracted from the generator for supplying the auxiliary system and energy storage system as a function of the rotor speed. Stored electricity in the energy storage system is then used to supplement the supply of power to the auxiliary power system. When the energy storage system is engaged, it is maintaining the auxiliary power consumption, meaning that power does not need to be extracted from the generator to fully cover this load to the auxiliaries.

(35) With reference to FIG. 3, the curve labelled P1 shows the total power that may be extracted from the generator as a function of the wind turbine rotor speed, minus electrical losses and losses associated with power conversion. If more power is extracted, the rotor would decelerate until it reaches a cut-out rotor speed. Without an energy storage system, the power from the generator must also be used to cover the auxiliary system. The curve denoted P1 shows the amount of production that is possible after reserving for the auxiliary load. Where the curve labelled P1 reaches zero kW (at rotational speed 326) the wind turbine would conventionally cut-out and stop producing power as it can no longer sustain its own production (if grid-disconnected) or maintain a positive power output (if on-grid).

(36) However, according to an embodiment of the present invention, with an energy storage system, as the rotor speed decreases below the limit where power extracted from the generator minus losses can no longer cover the auxiliary consumption, the power needed can be supplemented or entirely provided from the energy storage system. This allows power production to continue down to the rotor speed (325) where the curve P1 is zero kW. The shaded area 330 in FIG. 3 shows the power that is delivered from the generator system, after losses, while the other shaded area 331 shows the power that is delivered from the energy storage system.

(37) In the method according to an embodiment of the present invention, the energy storage system gradually supplements the auxiliary supply as the rotor speed decreases. Thus, according to an embodiment of the present invention, the second amount P2 of power increases with increasing rotor speed. Further, according to an embodiment of the present invention, the first amount of power decreases with decreasing rotor speed.

(38) Embodiments of the present invention may maintain the charge in the energy storage system and continuously operate down to even lower wind speeds than normal or conventionally, if the system is engaged, giving the aspect of low-wind ride-through capability.

(39) Embodiments of the present invention are intended for use in grid-disconnected turbines or turbines with a power-limited grid connection. For fully on-grid wind turbines with an energy storage system, the low-wind ride-through functionality can however also be used when it is advantageous for example to maintain operation of the wind turbine. This might be beneficial in the cases of wind turbines with power conversion systems that take a long time to re-start once they cut-out or shut-down. To be able to ride-through a short-duration low-wind period could therefore be beneficial for an on-grid wind turbine as well as for an off-grid wind turbine.

(40) According to an embodiment of the present invention, the energy storage system may be utilized to temporarily supplement the supply of the power needed by the auxiliary equipment. It may avoid or at least delay a shut-down of a wind turbine power production for too-low wind, when the wind speed is low only momentarily and keeps the turbine operating. This may have the advantage of avoiding delays associated with the re-starting a shut-down wind turbine once sufficient wind conditions return. For grid-disconnected wind turbines this may conserve energy and may allow for more continuous operation. For on-grid wind turbines this may improve energy production by avoiding delays and discontinuing and re-starting of power production. In a wind farm or individual wind turbines operating in an island mode or self-sustained operation mode, it is possible that they may be utilizing embodiments of the present invention. It may be possible to detect if the turbine is able to remain in operation at low wind speeds while energy is being drained from an energy storage system.

(41) An embodiment of the present invention consists of a wind turbine, an electrical storage system, and an operational strategy which may be used to eliminate or offset the amount of power which is consumed from the wind turbine's power conversion system to provide power for a wind turbine's auxiliary systems. The electrical storage system may be integrated into the wind turbine's electrical system as shown in the two examples below.

(42) In FIGS. 1 and 2, there is a wind turbine rotor, a generator and various electrical apparatus necessary for conditioning power for the electrical grid. The FIGS. 1 and 2 show a circuit for supplying power to an auxiliary system. This auxiliary system consists of the electrical consumers within the turbine. An energy storage system may be connected in such a way that it may provide power to the auxiliary network. FIG. 1 shows an inline variant where power for the auxiliary network may flow through the energy storage system. FIG. 2 shows a line-interactive variant where the energy storage system may supplement power flow.

(43) In both examples shown in FIGS. 1 and 2, it is possible for the energy storage system to supply power to the auxiliary network while the auxiliary network is disconnected from the grid using an auxiliary circuit breaker.

(44) The energy storage system may consist of a battery electric storage system, but other solutions may exist such as super capacitors, flywheels, hydrogen electrolysis and fuel cell systems or other energy storage systems. In the case of FIG. 2, the energy storage system may be comprised of a diesel or petrol generator (where the stored energy is in the form of diesel or petrol fuel). Other ways of connecting the energy storage system to the wind turbine's electrical system may also be used. The fundamental design element is that there is an energy storage system connected to the auxiliary network within the wind turbine.

(45) Although the present invention has been disclosed in the form of embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

(46) For the sake of clarity, it is to be understood that the use of a or an throughout this application does not exclude a plurality, and comprising does not exclude other steps or elements.