As grid measurement and control grows in software complexity it is important to have enough processing power installed in the right locations to enable eloquent, robust systems. Every CompactRIO controller has a combination of a core processor and an FPGA, both of which are programmable using the LabVIEW development environment.
Figure 3. The LabVIEW RIO architecture combines a processor, FPGA, and I/O elements. These hardware elements, combined with LabVIEW development software, are building blocks for embedded systems that help design measurement and control devices in less time than traditional methods and empower domain experts to create their own solutions rather than relying on a team of embedded developers.
The core processors available range from dual core ARM9s clocked at 667 Mhz/core to a quad-core INTEL processor clocked at 1.91 GHz/core. The core processor typically handles system functions such as file I/O, disk management, web services, protocol communication, and freely programmable computational algorithms. As a benchmark, the cRIO-9068 controller running the shipping version of the Open PMU Project for LabVIEW uses less than 25% of the core processors resources to run the PMU algorithm for 2x 3-phase busses.
The FPGA has multiple functions for utility applications. It is often used as a co-processing element to handle intensive in-line signal processing performed on sampled waveforms from the ADCs. Common signal processing for 50/60 Hz systems includes zero-cross detection, resampling of the waveform to constant phase angle, and filtering for enhanced zero-cross detection or other specific algorithms.
Other functions of the FPGA include synchronous time stamping from a GPS clock to an ADC sample point for synchrophasor measurements, and high speed input/output control for relay applications.
There are multiple silicon level technologies, such as FPGAs, DSPs, and ASICs, that are used today in utility grid applications for synchronization and co-processing. FPGAs bring some distinct benefits to the NI technology platform that are critical to helping with future utility equipment strategies.
- The firmware of an FPGA can be changed once the controller is deployed in the field. This is critical as the processing algorithms may need to change to better capture different power quality phenomena in the future. Years of algorithm research can be applied to the field with a software upgrade rather than a new equipment purchase. ASICs by contrast, are very cost effective in ultra-high volumes but the technology is locked at the time of manufacturing which can lead to stale instrumentation once standards change or new problems emerge.
- FPGA technology has evolved to blend multiple processing elements into a single die. FPGAs of today come with logic fabric, DSP slices, and some even contain processing cores. This flexibility makes them an ideal fit for platform based designs as platforms need to serve a variety of applications with fewer, more abstract design elements.
Traditionally, FPGA design involves special, low level design tools and years of school work to establish proficiency. NI products with an FPGA, such as CompactRIO, are programmed with LabVIEW and require less effort to establish a working knowlege.