Pitch control battery backup methods and system

[0001] This invention relates generally to wind turbine energy systems and more particularly to pitch control systems for wind turbines.

[0002] In one known wind turbine, a pitch control system having a fully regenerative silicon controlled rectifier (SCR) bridge drives a 4.2 KW series DC motor. This type of system has been used in servo motor drives for many years and is commercially available. The SCR drive has the advantage of simplicity, but may not be able to deliver the level of pitch system performance that may be needed in newer and/or larger wind turbines.

[0003] In the event of a loss of AC input power, at least one known wind turbine system pitches the blades of the wind turbine using emergency pitch batteries. The blades are pitched to a position that would prevent blade overspeed. The AC voltage drop is sensed by the pitch control system and the emergency pitch system is activated. The wind turbine control system modulates the emergency pitch system and attempts to keep the hub rotational speed below overspeed limits. In many cases, the turbine control issues a fault and stops the turbine. However, known wind turbine systems use DC link capacitors and an H bridge power converter circuit, and do not have the ability to pitch the blades using this circuit once the small amount of energy stored in the DC link capacitors is depleted.

[0004] One aspect of the present invention therefore provides a method for controlling a pitch control system of a wind turbine. The method includes providing a charged backup battery configured to supply no energy to a DC link when full AC input power is available, wherein the DC link includes a DC link capacitor. The method further includes using energy stored in the DC link capacitor to operate a pitch control system during a loss or dip of AC input power, and maintaining charge on the DC link capacitor using the charged backup battery as voltage across the DC link capacitor drops during the operation of the pitch control system.

[0005] In another aspect, the present invention provides an apparatus for controlling pitch of a blade of a wind turbine. The apparatus includes a pitch control system and a DC link having a DC link capacitor. The DC link is configured to provide power to the pitch control system. Also included is a source of AC input power to provide power to the DC link, and a backup battery configured to supply no energy to the DC link when full AC input power is available. The apparatus is configured to use energy stored in the DC link capacitor to operate the pitch control system during a loss or dip of AC input power, and maintain charge on the DC link capacitor using the backup battery as voltage across the DC link capacitor drops during the operation of the pitch control system.

[0006] In yet another aspect, the present invention provides a wind turbine that includes at least one blade and a generator coupled to the blade and configured to generate AC power. The wind turbine further includes a pitch control system configured to control a pitch of the blade about an axis, a DC link having a DC link capacitor and configured to provide power to the pitch control system, and a source of AC input power to provide power to the DC link. The source of AC power is not necessarily the generator. The wind turbine also includes a backup battery configured to supply no energy to the DC link when full AC input power is available. The wind turbine is configured to use energy stored in the DC link capacitor to operate the pitch control system during a loss or dip of AC input power, and maintain charge on the DC link capacitor using the backup battery as voltage across the DC link capacitor drops during the operation of the pitch control system.

[0007] Configurations of the present invention are thus able to provide battery supported operation of pitch control motor drives, which increases the availability of the wind turbine by allowing operation through grid disturbances.

[0014] In some configurations of the present invention, a single wind turbine pitch control design has cost and performance advantages over known systems. A single wind turbine motor drive is provided with a non-regenerative bridge supplying a DC voltage to an H bridge that comprises four active switching devices (e.g., paralleled MOSFETs in some configurations). A DC link capacitor smooths the DC link voltage and acts as an energy sink and source for the series DC motor. This design also includes an emergency pitch system using batteries and contactors to pitch the blades to a featured position.

[0015] In some configurations and referring to FIG. 1, a wind turbine 100 comprises a nacelle 102 housing a generator (not shown in FIG. 1). Nacelle 102 is mounted atop a tall tower 104, only a portion of which is shown in FIG. 1. Wind turbine 100 also comprises a rotor 106 that includes one or more rotor blades 108 attached to a rotating hub 110. Although wind turbine 100 illustrated in FIG. 1 includes three rotor blades 108, there are no specific limits on the number of rotor blades 108 required by the present invention.

[0016] Referring to FIG. 2, various components are housed in nacelle 102 atop tower 104 of wind turbine 100. The height of tower 104 is selected based upon factors and conditions known in the art. In some configurations, one or more microcontrollers within control panel 112 comprise a control system are used for overall system monitoring and control including pitch and speed regulation, high-speed shaft and yaw brake application, yaw and pump motor application and fault monitoring. Alternative distributed or centralized control architectures are used in some configurations.

[0017] In some configurations, the control system provides control signals to a variable blade pitch drive 114 to control the pitch of blades 108 (not shown in FIG. 2) that drive hub 110 as a result of wind. In the illustrated configuration, hub 110 receives three blades 108, but other configurations can utilize any number of blades. In some configurations, the pitches of blades 108 are individually controlled by blade pitch drive 114. Hub 110 and blades 108 together comprise wind turbine rotor 106.

[0018] The drive train of the wind turbine includes a main rotor shaft 116 (also referred to as a “low speed shaft”) connected to hub 110 and supported by a main bearing 130 and, at an opposite end of shaft 116, to a gear box 118. Gear box 118, in some configurations, utilizes a dual path geometry to drive an enclosed high speed shaft. The high speed shaft (not shown in FIG. 2) is used to drive generator 120, which is mounted on main frame 132. In some configurations, rotor torque is transmitted via coupling 122. Generator 120 may be of any suitable type, for example, a wound rotor induction generator.

[0019] Yaw drive 124 and yaw deck 126 provide a yaw orientation system for wind turbine 100. Wind vane 128 provides information for the yaw orientation system, including measured instantaneous wind direction and wind speed at the wind turbine. In some configurations, the yaw system is mounted on a flange provided atop tower 104.

[0020] In some configurations and referring to FIG. 3, a control system 300 for wind turbine 100 includes a bus 302 or other communications device to communicate information. Processor(s) 304 are coupled to bus 302 to process information, including information from sensors configured to measure displacements or moments. Control system 300 further includes random access memory (RAM) 306 and/or other storage device(s) 308. RAM 306 and storage device(s) 308 are coupled to bus 302 to store and transfer information and instructions to be executed by processor(s) 304. RAM 306 (and also storage device(s) 308, if required) can also be used to store temporary variables or other intermediate information during execution of instructions by processor(s) 304. Control system 300 can also include read only memory (ROM) and or other static storage device 310, which is coupled to bus 302 to store and provide static (i.e., non-changing) information and instructions to processor(s) 304. Input/output device(s) 312 can include any device known in the art to provide input data to control system 300 and to provide yaw control and pitch control outputs. Instructions are provided to memory from a storage device, such as magnetic disk, a read-only memory (ROM) integrated circuit, CD-ROM, DVD, via a remote connection that is either wired or wireless providing access to one or more electronically-accessible media, etc. In some embodiments, hard-wired circuitry can be used in place of or in combination with software instructions. Thus, execution of sequences of instructions is not limited to any specific combination of hardware circuitry and software instructions. Sensor interface 314 is an interface that allows control system 300 to communicate with one or more sensors. Sensor interface 314 can be or can comprise, for example, one or more analog-to-digital converters that convert analog signals into digital signals that can be used by processor(s) 304.

[0021] In some configurations of the present invention and referring to FIG. 4, in the event of a loss of AC input power from a source 400 and to prevent turbine overspeed, blades are pitched using a MOSFET 402 based power converter 404. Power converter 404 comprises part of a pitch control system 406. (For notational convenience, as used herein, AC input source 400 refers to a rectifier bridge or an IGBT or MOSFET bridge. It is understood that this bridge is intended to be electrified by a generator, a power line, a power grid, or some other source of AC power, which may or may not comprise generator 120.) A backup battery 408 is provided to allow pitching of blades 108 (shown in FIG. 1) in the event of AC input power loss or a power dip. Battery 408 (which can comprise one or more electrical cells or a plurality of multicell batteries, or any combination thereof) is connected to DC link 410 of through a diode 412 and a fuse 414. Under normal conditions, diode 412 is reverse biased and no current flow occurs from battery 408 to DC link 410. In this condition, battery 408 is charged and its condition monitored, but it supplies no energy to DC link 410.

[0022] When the DC link 410 voltage dips to below the voltage of battery 408, current flows out of battery 408 through diode 412 and fuse 414 to maintain charge on DC link capacitor 416. Diode 412 prevents uncontrolled charging of battery 408 when the DC link voltage is higher than the battery voltage. Fuse 414 prevents damage to battery 408 in the event of a short circuit on DC link 410. Backup battery 408 of DC link 410 allows pitch control system 406 to maintain active control of blade 108 position throughout an AC power loss or dip event.

[0023] In some configurations of the present invention and referring to FIGS. 5A and 5B, a multi-drive wind turbine pitch control system is provided. One non-regenerative source 400 of AC power can supply multiple pitch control systems 406 using a common DC link 510. Common DC link 510 is supported by the use of a battery 408. In some configurations, pitch control systems 406 on common DC link 510 swap real power during operation and reduce power demand on battery 408 in the event of an AC power outage or dip. Also, in some configurations and referring to FIGS. 6A and 6B, pitch control systems 406 with a common DC link 510 supplied by a fully regenerative IGBT or MOSFET 602 controlled source 600. Battery 408 is used in this configuration to support DC link 510 in the event of power outages.

[0024] It will thus be appreciated that configurations of the present invention are able to provide battery supported operation of pitch control motor drives, which increases the availability of the wind turbine by allowing operation through grid disturbances.

[0025] Configurations of the present invention are not limited to wind turbines having any specific number of blades. For example, turbines with one, two, or three blades (or more) can use configurations of the present invention to control blade angle in the event of an AC power loss, therefore increasing turbine availability over those turbines that do not have DC link pitch control capability.

[0026] While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.