Currently, there are more than 750 wind turbines in operation in Australia. Together, these generate nearly 1.5 gigawatts (GW) of power, or roughly 1.3 per cent of the electricity now being consumed in Australia.
The rapid expansion of wind power is partly the result of increased turbine size and the continuous expansion of wind farms. It is also due to technological improvements in the wind turbines themselves. Better rotor blade aerodynamics, more efficient generators and optimised supervisory control systems make today’s wind turbines more efficient than ever before.
This enhanced technology presents engineers with some new challenges. Wind turbines are highly complex systems in which mechanical, hydraulic, and electronic systems must efficiently work together. A complex supervisory control system ensures each of these integrated systems properly responds to different environmental conditions, such as changing wind speeds.
Streamlined and integrated development
A complete system such as a wind turbine is an assembly of many different components. These include hydraulic system components, electric machine components, mechanical machine components and embedded software. The design of each system component is often done using a specialized design tool, where the system ‘integration’ effects are often ignored.
In a traditional development process, the designs may be created in separate software and simulation environments, with separate methods for capturing system requirements, such as maximum yaw rate or cut-in wind speed. Because these requirements are not incorporated into the development process, engineers are often unable to determine if design changes will prevent the system from meeting them. Furthermore, if the requirements are incorrect or incomplete, this may not be detected until the final phase of development when these errors are expensive to fix.
Engineers working in separate software environments may not have the option of testing integrated design in simulation. If the teams developing the generator and the supervisory control system work separately, integration problems can only be detected after hardware prototypes have been produced. Moreover, cost and safety prohibit exhaustive testing on hardware prototypes. This means that systems are overdesigned (and are therefore less efficient) to make sure the turbine does not fail.
Contradictory goals
Various control systems with competing goals must interact with each other, and this creates a difficult design challenge.
For example, the monitoring system for the entire wind turbine has to ensure that the turbine generates electricity as frequently as possible, but that it also shuts down when required to protect the individual parts from any unnecessary wear and tear. It also has to react to any internal failures to prevent the turbine from becoming unstable and destroying itself.
A smooth and continuous development process
Model-Based Design overcomes these problems by using a single environment for modelling and simulation, linking everything directly to the specifications.
Engineers using Model-Based Design develop a computer model of the systems being developed for simulation. This model is then used throughout the development process, from defining the system requirements through to the automatic generation of production code. Systems that will interact can be tested together and optimised, and the controller hardware can be tested before any hardware prototypes are built. The generation of embedded software directly from the computer model improves communication between teams and makes it easier to spot integration problems early in the development process.
From the model to automatic code generation
Using Model-Based Design, a wind turbine is modelled entirely in a software program environment. The model of the physical system is connected to the control algorithm and various inputs, such as wind speed and direction. The specifications and requirement documents are connected directly to the model via bidirectional links using the program’s verification and validation. This allows designers to easily check whether all requirements are still being satisfied at each stage of development.
Engineers perform system-level analyses to select technologies and determine requirements for the system. For the yaw actuation system – which rotates the wind turbine so the blades face the wind – the model can start as a single ideal torque source, and then be incrementally refined to include four individual motors, motor drivers, gearbox, and other details. This gradual progression in design enables engineers to test their design every step of the way, validating and refining overall system requirements.
All subsystems can be integrated in the simulation environment at an early stage of development. In each step, the trade-off of model fidelity and simulation speed can be balanced so engineers can both iterate quickly and check for integration issues. A three-dimensional animation of the system and plots of simulation data show the developers how the wind turbine reacts under varying conditions.
To test control code and the controller hardware, hardware-in-the-loop tests can be used instead of wind turbine prototypes.
Integration at an early stage
Early integration in simulation makes it easier for engineers to optimise a wind turbine’s design, by selecting the proper technology and checking for integration issues. Using the simulation, the whole wind turbine can be tested under a wider range of weather conditions than would be possible on a real system. Model-based Design enables the system and the controller hardware to be tested before hardware prototypes are even made, leading to even more efficient and reliable turbine designs.
Steve Miller is responsible for the technical marketing of the physical modelling tools at The MathWorks. He joined The MathWorks as an Application Engineer in 2005 and moved to the Design Automation Marketing group at The MathWorks in 2006.
