Wind Turbines

System Challenges
The primary concern in the design of a medium-to-large wind turbine systems centers on the protection and reliability of the system with a somewhat secondary goal of power efficiency. This is due to the fact that wind turbines have large rotating masses residing in exposed locations and that the turbine structural and mechanical costs dominate over electronics costs. This is especially true for off-shore wind farms where maintenance access is both limited and expensive and can frequently be dangerous. To ensure that that the turbine operates at all times within its safe operating area, a great deal of attention needs to be paid to monitoring all parameters which can affect it.

Control / Processing
Normally there are at least three controllers in the power chain of a typical wind turbine. The first controller is usually either an FPGA or a very high performance DSP engine. ADI's fourth generation of SHARC® Processors, which includes the ADSP-21469 and ADSP-21489, provide popular DSPs that are commonly used in this application. All devices are completely code-compatible and are highly integrated with memory and a number of different peripherals. Lower cost SHARC processors such as the ADSP-21488 and ADSP-21489 are also available.

A second processor acts as a controller for grid-side duties and a good candidate here is ADI's latest, low power, fixed point Blackfin® DSP controller family. The BF50x family delivers 400MHz of processing performance with a dual multiply and accumulate architecture equivalent to 800 MegaMACS of performance. It also includes an integrated 12 bit Dual SAR ADC which delivers 11.7 ENOBs. With this advanced converter performance, product designs can now offer greater accuracy than ever before.

The third processor in the system acts as a communications processor to handle all communication tasks. Each turbine in a large farm employs a wireless communications system to communicate data such as turbine activity, inverter activity, power efficiency and numerous health indicators to the central control monitor. A suitable communications controller is ADI's new ADuCRF101 processor based on a Cortex M3 core from ARM. This combines a processor and transceiver in the same package and operates in the 433/868/915 MHz ISM/SRD bands. It offers class leading blocking resilience (60dBm @+/-2MHz with -104dB signal) and high sensitivity (-111dBm ' 9.6kbps).

Communications
Within a single turbine the various controllers communicate with each other via wired technology. When communicating at high data rates or over the relatively long distances within a turbine, differential data transmission offers superior performance to single-ended transmission. Popular protocols for this communication task are RS-485 and CAN. Analog Devices offers a wide range of iCoupler®-based isolated RS-485/RS-422 transceivers to suit this application with the ADM248xE and ADM258xE families which include integrated isolated dc/dc converters. More recently, Analog Devices’ has released the first of a family of isolated CAN transceivers, the ADM3052/3053, with and without an integrated isolated dc/dc converter. For proprietary protocols there are also numerous standard iCouplers available such as the ADuM140x family, which are quad channel isolators.

Measurement / Sensing
For current sensing, galvanic isolation is mandatory and current transformers (CTs) have been widely used to date for this purpose while Hall effect and shunt resistors have been less popular here due to the high currents involved. Each sensor type has its own advantages and disadvantages but all require precision, low noise, low power op amps like ADI’s OPX177 family to complete the signal conditioning demanded by the signals of different current sensors.

For position sensing of the gearbox output shaft high resolution resolvers are employed due to their mechanical integrity and ability to work in harsh environments. Suitable RDCs for this application are ADI's AD2S1205 and AD2S1210 components.

Vibration analysis is an important tool in early identification of developing problems in rotating machines. Bad bearings, worn gears, loose fittings, and misaligned equipment, especially in the larger 1MW + wind turbines, can have a profound impact on the operational lifetime and maintenance costs of grid-connected wind turbines. For vibration analysis and predictive maintenance purposes the new iSensor® product, the ADIS16227, is uniquely capable of delivering an embedded vibration monitoring system. Built around ADI’s own tri-axial MEMS technology, this module offers a sophisticated suite of FFT analysis algorithms, programmable spectral alarm bands and user-configurable multimode operation to monitor, detect, analyze and capture, in a single module, all pertinent vibration data.