John Johnson considers the use of FPGAs to tackle the design challenges of smart metering systems
Legacy power infrastructure is intrinsically inefficient, aging and the operation of it is often harmful to the environment.
We hear more stories of older power grid infrastructure breaking down and damaging the communities the infrastructure is intended to serve.
Standards organisations and engineers have risen to the challenge, promising to solve many of these aforementioned drawbacks. The so-called “smart grid” embodies many of these solutions.
Implementing a smart grid system offers the engineer significant design challenges as these systems must have longevity, from not only a reliability standpoint but also from the perspectives of performance and functionality.
A modern power delivery architecture includes power generation, transmission and distribution and consumers. The smart grid differs from legacy systems in many aspects, including new technologies such as renewable energy sources, energy storage, and instrumentation (including consumer metering and grid performance analysis).
Optimum control of the grid hinges on the presence of extensive communications and electrical power networks, the close monitoring and control of grid parameters, and provisions to ensure reliability and security.
Prior to the mid-1990s, no global power grid standards existed that enabled energy providers to deploy interchangeable equipment. To facilitate improved control and flexibility, the grid needed to transform from a single network of transmission lines to a pair of networks comprising communications and power distribution.
The International Eletrotechnical Commission (IEC) developed a set of core standards that addressed substation architecture, communications, and security, as well as timing and synchronization.
Work began on the IEC 61850 standard, Communication Networks and Systems in Substations, in 1995 when representatives from the IEC, the American National Standards Institute (ANSI), and others collaborated on a new way of thinking about the control of substations by implementing robust communications networks as well as a framework to facilitate automation.
Since the inception of IEC 61850 and as system knowledge and requirements have evolved, incremental capabilities have been added to broaden and refine the standard's performance and functionality, including areas like hydro power, PV power plants, and distributed energy resources.
From an internal substation infrastructure perspective, IEC 61850 facilitates interoperability, flexibility, and control by replacing hardwired implementations with a network of substation equipment communicating over fibre optic cable. While this network solves a number of problems associated with flexibility and interoperability, it creates new challenges as well.
For example, the fibre optic network replaces low latency copper wire connections. To facilitate this network, IEC 61850 provides support for special messaging that bypasses layers of the communication stack to reduce latency.
Substation automation standards like IEC 61850 specify that no single point of failure causes a system malfunction; therefore, substation architectures employ redundancy for all mission critical components.
Also, substation system engineers must meet recovery time specifications (the time required to identify and restore a substation service after a failure). IEC61850 prescribed the use of IEC62439-3 (Parallel Redundancy Protocol) and High-Availability Seamless Redundancy).
In order to make the smart grid “smart,” power-grid equipment includes a combination of signal processing, communications management, dedicated hardware blocks and other peripherals. To accomplish this, legacy systems typically incorporate a digital signal processor, a central processor unit (CPU) and an FPGA.
As the capabilities and levels of integration of FPGAs have increased, several smart grid applications have incorporated an FPGA or an SoC to implement all of these blocks, affording superior reliability, maintainability and cost.
Today, equipment designers implement their grid communications products on FPGAs and SoCs.
An example of FPGAs being used in a smart-grid applications is the 4-port Ethernet switch with support for HSR, PRP, and IEEE1588-2008 offered by Altera and its smart grid design partner, Flexibilis.
The design is a 4-port switch that is expandable to 8 ports. It supports 10/100/1000 Ethernet, IEC 62439-3-compliant implementations of PRP/HSR, support for IEEE1588-2008, and requires no external memory.
Today’s 28nm FPGAs and SoCs possess several qualities that help enhance smart grid equipment reliability. High levels of integration reduce the number of components required, thereby enhancing MBTF/FIT rate performance.
Features like error correction code memory coverage and the use of multiple processors help to insure reliable operation. Some configurations implement a small RISC core within the FPGA fabric; while others simply lock down the level-1 cache of one of the two ARM Cortex-A9 processor cores and employ the dedicated core for diagnostic (watchdog) purposes.
For example, a 28nm SoCs deliver up to 4000MIPS using the dual-core ARM Cortex-A9 processor. A NEON coprocessor with double-precision floating point accompanies each core. Each processor includes 32kbyte of L1 coherent cache and both cores share 512dB of L2 cache.
While the ARM cores afford good performance for all but the most computing-intensive applications, applications that require real-time computational capability often implement hardware acceleration in the FPGA fabric.
Smart grid equipment manufacturers require a spectrum of performance levels across product offerings. Features common to all products (e.g., PRP/HSR) can share the same implementation across FPGA and SoC families, thus enabling reuse and cost/performance optimisation.
Providing solutions for products that have long product life cycles goes beyond reliability and a commitment to provide the solution for the life of the product. The ability to reconfigure and upgrade products (in either manufacturing, production, or development) is critical, particularly as standards like IEC 62351evolve over time.
FPGAs help mitigate this problem by providing scalability and reconfigurability to implement product updates that go beyond a simple software change.
