Controlling the Motors in Wind Turbines

Wind turbines are described as rotating machines which convert the kinetic energy of wind into mechanical energy. This energy, in turn, is changed into electricity.

Turbines are utilized in wind farms for producing electric power at a commercial scale. They have three blades and motors controlled by servo drives that point them in the wind direction. These blades are very efficient, with low torque ripple contributing to excellent overall reliability, and have high tip speeds that are around six times the speed of the wind.

wind turbine servo drives

The length of the blades range between 20 and 40 m, or more, and they can be controlled through Elmo’s high-performance digital servo controller—the Tiger 50/600. The Eagle 35/200 from Elmo is a compact, intelligent, high-power servo drive that is utilized as a backup drive to manage system operations in the event of a malfunction or emergency.

The motor blades rotate at 10 to 22 rotations per minute (RPM), although the more sophisticated versions operate at a continuous speed. In this application solution, the motor blades—controlled by the servo drives—constantly change their angle with respect to the wind flow to keep a continuous rotational speed. Safety shut-down features are also incorporated in all the turbines to prevent damage at high wind speeds.

The Challenge

The following challenges are faced when developing an application solution built on Elmo’s products for a wind turbine:

  • The potential to regulate the blades driven by DC brushless motors
  • The requirement for precise, high-speed control of the three blades of the wind turbine
  • The need to offer a solution based on products that conform to safety requirements and have backup/redundancy capabilities
  • The necessity to provide a highly reliable solution in variable and extreme conditions
  • The potential to offer sophisticated programming capabilities within the drive to allow it to react to unforeseen situations
  • The need to develop a solution that utilizes minimum space and is compact
  • The potential to link directly to a three-phase mains supply without the necessity for a DC power supply
  • The need to offer Absolute Encoder support
  • The requirement to deliver a low-cost, high-power, and intelligent motion control solution

Elmo’s Solution

Wind turbines have limited space for the installation of the servo drives, hence compact electronics with extremely high-power motor drives are needed to deliver the required high torque and to precisely control the blades’ speed.

The Eagle and Tiger digital drives are designed to deliver high performance and high-power density where safety is a major concern. The Tiger digital drive was selected as the key driver because of its high power, small size, and potential to support around 600 VDC bus. This fully digital servo drive can drive up to 50 A of constant current needed for the high torque that is required for driving the wind power blades at rapid speed.

High current servo drive

Eagle: High current servo drive 100 A/100 V, 18 A/400 V

Compact high-voltage servo drive

Gold Tiger: Compact high-voltage servo drive 16 A/400 V DC, 12 A/800 V DC, 12 A/900 V DC

Technical Description

The application implementation is based on established, ready-to-use products, utilizing the EAG 35/200 and TIG 50/600 as the auxiliary and main system controllers, respectively. The products were designed for very high-performance servo systems that are often employed in high-power military applications. The MIL-STD compliant drives can work in extended environmental conditions (EEC).

The Tiger digital drive is directly powered by three-phase mains power and there is no need for an extra DC power supply since it includes an internal integrated DC power supply. The Eagle digital drive acts as an auxiliary backup that additionally boosts system reliability. Both the EAG 35/200 and the TIG 50/600 are hugely dependable products that have been incorporated in several military applications. The drives’ reliability is equal to that of the DC brushless motor of a wind turbine.

Product Highlights

The key system controller interacts with the auxiliary and main drive controllers through CANopen communication. To facilitate communications redundancy for constant monitoring, an optional RS-232 channel can be supplied to the system controller and also a secondary channel in the event of a fault.

Elmo’s multi-axis controller, called the Maestro, is the upper controller of the system. It communicates with the host via Ethernet or Modbus protocols and controls the system’s standard operating modes. This is performed using CANopen, PWM or P&D commands, RS-232 commands, and analog commands.

The Maestro communicates with both the drives and also tracks and detects the status of the system, like motion faults, drive faults, communication faults, sensor faults, AC power loss, etc. and responds as needed.

The operation of both the drives is controlled by the main system controller over the RS-232 or CANopen communication channel. The main system controller simultaneously functions as a redundant backup, utilizing I/O lines to regulate and track each drive and other system elements.

The main driver works under usual conditions where there is AC mains power. If there is a dip in the mains AC power below a specific threshold level, then the auxiliary drive will begin to work from this source and will take control over the motor.

Operational under standard conditions, the main drive utilizes the absolute encoder (or any other encoder) of the motor. The auxiliary drive remains active only when the mains voltage power is off or the main drive malfunctions. It enables redundant position control of the motor. The system also includes redundancy for the absolute encoder feedback.

Through the I/O controls, the upper controller enables switching between the motor phases and the main drive. The system controller controls the switching logic. Each drive unit can be fully programmed and offers multi-level intelligence that considerably boosts the system’s ability to respond accurately and on time to any fault condition.

In addition, heartbeat is supported over CANopen communication channel to identify a faulty drive. The implementation comprises watchdog implementations at numerous levels, like a lost I/O signal to the relays, a lost CANopen communication, etc., to raise the safety level of the system. Both drives are capable of supporting brake commands to stop the motor when required.

Extra I/O lines are linked between the numerous components of the system (safety and relays board, drives, and system controller) that can be utilized as an extra safety control and bypass. Furthermore, the drives’ distributed intelligence can be utilized to apply extra safety logic. The temperature sensor of the motor is coupled to the main drive.

Why Elmo

  • Networking and distributed intelligence
  • Robust servo and motion control technology
  • Elmo’s advanced ET servo drives can work between –0 °C and +60 °C. This means, there is no need for air conditioning to cool or warm the drives. This streamlines the complexity of the system and considerably increases its reliability.
  • The use of Elmo’s TIG 50/600 facilitates a direct connection to the mains VAC electricity network. The addition of an extra bulky, high-power isolation transformer eliminates the need to step down the voltage.
  • Low maintenance, with high performance and reliability is needed to operate the DC brushless solution.
  • The proprietary technology of Elmo enables DC brushless motors to be used in “sensorless-stepper” mode. Additional backup feedback is not needed in emergency conditions.
  • The performance of Elmo’s solution is improved by advanced programming and versatility.
  • A regular DC brushless motor with an absolute encoder can be used with Elmo’s state-of-the-art drives.
  • High efficiency
  • High-power density products in a highly compact overall solution

This information has been sourced, reviewed and adapted from materials provided by Elmo Motion Control Ltd.

For more information on this source, please visit Elmo Motion Control Ltd.

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