Phil Ebbert, VP of Engineering at Riedon, Inc.
By achieving high efficiency levels, environmental guidelines can be adhered to and electricity consumption costs made more manageable. Conversely, elevated efficiency levels must be maintained in places where energy is being generated, so that it can always be used to full effect.
There are many high-power applications where accurate DC current monitoring will be pivotal in increasing the efficiency of such systems - thereby allowing operational cost and ecological benefits to be derived. By being able to get constantly updated current values, functions and processes may be better controlled, and energy wastage avoided.
In the past, getting good quality current measurement data from high-power system implementations proved challenging. It's only recently that the situation has actually improved - thanks to innovations made by the technical team at Riedon.
Sensor Options Available for High-Power Current Monitoring
When looking to take current measurements from high-power systems, there are two main routes that can be followed. Engineers can either employ a conventional passive shunt current sensing methodology, or install Hall Effect sensors into their systems instead.
For shunt current sensing a low-value resistance is placed in the conductor carrying the current intended to be measured. A potential difference is created across this resistive element, which is directly proportional to the current present - facilitating extrapolation. Shunts are inexpensive, compact and simple to integrate. They give consistently stable readings (with their accuracy unaffected by other influences).
Though they provide a straightforward and cost-effective means for obtaining accurate current measurements, there are downsides that engineers must be aware of. Since the resistive element is directly in the system, this has to be considered as an intrusive form of measurement. A certain amount of power ends up being dissipated as heat, because of the resistance. This is problematic when dealing with higher current levels (i.e. those above 100A). In such situations, the resistive element will represent a significant power loss.
Hall Effect current sensors offer an alternative to the shunt approach, in which the magnetic field around the conductor induces a current within the sensor itself. The induced current will proportionally correspond to the size of the current flowing through the conductor. This results in a non-intrusive measurement, with no direct electrical connection (thereby eliminating the shunt-related power losses just described).
As with shunt arrangements, Hall Effect measurement strategies have issues associated with them. These sensors are more costly, potentially putting them outside the acceptable budget limitations defined for some applications. They are also bulkier, making them difficult to utilize in space-constrained systems. Their operational temperature range isn’t as broad as shunts, so yet again there could be applications in which conditions are simply too demanding for them.
By far the biggest concerns with Hall Effect sensors will be in terms of accuracy. Firstly, how close they can be positioned in respect of the conductor being monitored will be critical. The bigger the air gap, the poorer the quality of data acquired. Secondly, the presence of nearby sources of electromagnetic interference (EMI) will be disruptive, meaning measurement data is similarly compromised. Thirdly, these sensors are prone to drift in their sensitivity - as they age and also because of exposure to thermal fluctuations. To combat this, regular recalibration work must be conducted, which adds to the ongoing running costs. Shunt device calibration is just done once, making it more economical and offering greater convenience too.
The characteristics that each of these current sensor types possesses has meant they are only suitable for attending to certain applications. Generally speaking, board level shunts are implemented when the currents being measured are below 50A, with Hall Effect sensors being responsible for current levels above this.
A multitude of different scenarios exist in which there’s a need for a current measurement solution that successfully combines the positive attributes of passive shunt and Hall Effect devices. Among the most prominent of these are uninterruptible power supplies (UPS), industrial drives, electric vehicle (EV) powertrains and renewable energy infrastructure. All of these need access to current measurement data with a very degree of accuracy, while simultaneously mitigating the implications of unwanted power losses.
Proprietary active shunt technology developed by Riedon reduces the resistance element within current measurement set-ups to an absolute minimum, by amplifying the potential difference measured across the resistive element. Consequently, much smaller current signals can be dealt with, andpower dissipation is negligible.
The Key Benefits of Active Shunt Technology
The underlying technology behind Smart Shunt is easily understandable. It takes a conventional passive shunt, then combines it with a high-precision isolated amplifier, so a differential output can be delivered. This allows the power losses that hindered passive shunts to be circumvented. These components are fabricated from a manganin alloy that keeps unit pricing low, making them much more financially attractive than Hall Effect sensors.
At the high current levels, Smart Shunt devices are substantially smaller and simpler to fit into systems than their Hall Effect sensor equivalents. They exhibit superior EMI resilience and aren’t prone to thermal or lifetime drift either. As they remain stable over both time and temperature, periodic recalibration work is no longer required, resulting in a lower total cost of ownership (TCO) for customers.
Riedon Smart Shunt devices have already seen widespread deployment in various high-power applications - bringing the current sensing accuracy needed without impinging on system efficiency. Always wanting to push things forward, the company continues to invest in product development within this area, so exciting new innovations can be introduced.
The New Breed of Smart Shunt Devices
Having announced its SSA Smart Shunt series back in 2020, Riedon was able to address growing needs throughout the industry for highly accurate, low-loss current measurement. Via in-depth discussion with customers using these sensors, the company identified where further enhancements could be made.
Based on customer feedback, it was apparent that real value would be gained by incorporating additional functionality - particularly the inclusion of a digital output. This was the motivation behind the next chapter in the Smart Shunt story.
Complementing the existing analog output SSA series, the new SSD series signifies a major step forward. These offer engineers the added convenience of a digital output, with clear integration benefits resulting. They are straightforward to use in brand new system designs or retrofit into legacy equipment.
All SSD series devices feature a 16-bit automotive-grade microcontroller, a 24-bit analog-to-digital converter (ADC), with buffered analog inputs, plus flash memory with error correction code (ECC) capabilities. With ±0.1% full-scale accuracy, they can determine current values from 100A (2kA peak) to 1kA (20kA peak). A sophisticated non-linear temperature compensation mechanism protects sensor accuracy against ambient temperature variations. Long-term sensor stability is assured, with less than ±0.1% deviation during 1000 hours of operation (at 60°C terminal temperature).
These components only occupy 68.8x80mm of board real estate. Their ambient operating temperature range spans from -40°C to +115°C, enabling them to withstand harsh application settings. For greater system design versatility, engineers can choose either RS485 or CANbus interfacing.
Smart Shunts in Action
There are many applications where Riedon Smart Shunt technology is now being leveraged, with automobile manufacturers and industrial OEMs among the client base. One interesting
application is the project being pursued by Purdue University, in West Lafayette Indiana, USA. Smart Shunt devices are being employed in its ‘DC Nanogrid House’.
This project’s objective is to evaluate the feasibility of DC power distribution throughout residential buildings, rather than having to rely on AC power instead. Purdue engineering staff and post-graduate students have retrofitted the entire house to run off a highly-efficient DC-powered nanogrid. By doing this, energy efficiency improvements may be realized, translating into estimated 12-15% savings off the average household’s electricity bills. The principles aren’t only applicable to domestic use either, major savings could be made by small communities of houses, university campuses, hospitals, etc.
For over 130 years electrical distribution has been AC-based, yet the equipment it powers within the home is nearly always DC-based (thus requiring individual conversions). Dynamics, such as increasing contribution from localized renewable energy generation and greater prevalence of energy storage (thanks to reductions in Li-Ion battery costs), are making DC much more relevant again. If AC current coming from the grid only has to be converted to DC once, and is thereafter accessible in that form all over the building, then there’s no longer a need for subsequent conversions (each of which otherwise resulting in power losses). On top of this, battery-stored energy and electricity coming from on-site renewable energy resources aren’t needlessly converted to AC and back again before they can be consumed (reducing wastage).
Another factor that cannot be overlooked is AC grid stability. In recent years there have been several occasions when extreme weather conditions brought about prolonged blackouts. Instead of being dependent on the AC grid, the DC Nanogrid House has energy autonomy properties. If there’s an outage, electricity can be supplied by roof-installed solar panels and by drawing from on-site battery reserves.
Several of the research team involved in the project now stay in the house - becoming part of a living experiment. Occupancy detection means air conditioning and lighting are only activated if people present in those rooms.
The electrical system architecture consists of four elements.
● Solar input
● The 48V lighting element
● A 380V bus for powering appliances
● An EV charging element
Every one of these needs’ accurate electricity monitoring capabilities, and has been fitted with an individual Smart Shunt for executing these measurement functions.
Click image to enlarge
Figure 2: The DC distribution panel with its four constituent elements
With the advent of the SSD series, deployed analog output devices are now being replaced by digital versions. This will expedite the monitoring/analysis process, for better comprehension of different aspects.
By providing a current sensing solution with considerably lower insertion resistance than passive shunt sensors, with much greater accuracy and operational stability than Hall Effect sensors, Smart Shunt devices are already opening up whole new opportunities for current monitoring within high-power systems. With the added bonus of digital interfacing the argument for using them has now got even stronger.