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Regardless of the type of system you are working on or the type of control system you are planning to use (whether it be a process control, motion control, or simple proportional integral derivative (PID) system), you can take advantage of new tools and platforms to improve your system. The National Instruments reconfigurable I/O (RIO) platform, which combines real-time technology with field-programmable gate array (FPGA) chips, provides a unique architecture you can use to design and implement controllers that have enhanced reliability, performance, and/or loop rates.
Software is a key part of this architecture. The NI software platform, which includes the LabVIEW graphical programming environment as well as the LabVIEW Real-Time, LabVIEW FPGA, and LabVIEW Control Design and Simulation modules, makes it easier for you to create embedded platforms without having in-depth knowledge about control systems, so you can focus on creating your applications, not on implementing them.
This article explores several use cases in which you can use the RIO architecture to design or test advanced control algorithms.
Advanced Motion Control/Cascade Control
One of the main benefits of using the NI RIO platform is the ease with which you can cascade different controllers. With the RIO architecture, one algorithm can run on the FPGA, which enables loop rates in the order of double-digit kilohertz while maintaining nanosecond determinism, while another algorithm can run on the real-time controller and take advantage of its powerful dual-precision floating point for complex math calculations. A perfect example of this architecture is with motion control applications in which the position/control loop runs on the processor and the high-speed current loop runs on the FPGA fabric.
Figure 1. This diagram shows the flow of cascade control.
High-Kilohertz PID
When referring to advanced control algorithms, consider the control loop rate instead of the software algorithm. Even standard control algorithms such as the ubiquitous PID are limited to loop rates in the order of low kilohertz when running on standard commercial off-the-shelf solutions. This might not be fast enough in systems where changes in the controlled variable happen in the order of one-tenth of a second.
Systems with such fast dynamics are becoming more common in industrial environments as machines are required to perform at higher throughputs with better quality. To illustrate this concept, view a case study from EUROelectronics, a company that developed a hydraulic die-casting press machine and needed to change between position and pressure control in the order of low milliseconds.
Multiple PID Loops Running in Parallel
A limiting factor of many industrial controllers is how expensive it is to build systems that implement multiple controls at multiple rates. These platforms typically require a single module for every control loop, which increases the number of hardware components needed for systems with a high number of inputs and outputs. By using RIO-based controllers, you can run many parallel PID loops on a single FPGA chip without adding extra hardware.
Industrial Hardware in the Loop (HIL)
In addition to advanced control design, you can take advantage of FPGA-based targets for control test or HIL applications. Imagine the following scenario: you must implement new code on your standard programmable logic controller (PLC), but the only real way to test it is to actually go onsite and run-test it. This is a lengthy and costly process and, furthermore, a risky one because it is not safe to exercise the system to check if the fail-safe code works properly.
You can simulate your plant using the RIO controller and FPGA to design and simulate your different sensors. With this setup, you can test your code for reliability as well as validate system performance and specifications in the design cycle, allowing for a more manageable design cycle with improved time to market.
Figure 2. This is an example of HIL simulation code.
Brushless Motor Control
Although electrical motors have been widely used in industry since the industrial revolution and the transition from steam engines to electrical engines, their usage has increased even more in recent years because of the rise of more environmentally friendly devices such as hybrid vehicles and new methods of harvesting energy, such as wind and wave turbines. However, new application areas present new challenges because motors must run longer and smoother and with lower maintenance costs.
With high speed, high torque to inertia ratio and quiet operation, brushless DC motors present several benefits over other electrical motor configurations. They do have some drawbacks, such as being more expensive to build and operate. By using a RIO architecture combined with advanced control algorithms, you can use new control algorithms such as field-oriented control (FOC) to increase motor performance and life.
Conclusion
You can use the RIO architecture in any control application without needing to be an expert in either embedded tools or FPGA development. NI tools make it easier to create and deploy your own custom advanced control applications.
View a video on cascade control.
- Javier Gutierrez
Javier Gutierrez is the product manager for LabVIEW simulation and control design tools and is responsible for managing contact with primary users of NI industrial control applications. Javier joined NI Spain in 2000 as an applications engineer, where he also held positions as a field sales engineer, district sales manager, and applications engineer manager. He transferred to the NI corporate office in December 2006. He has the equivalent of an electrical engineering degree with a master's in controls from the University of Malaga, Spain.
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