1. A lot of the current buzz in electronic systems development is about “smart” products, and the ability to oversee the performance and functionality of these solutions. Between competition and consumer expectations, a product on the market today must perform its functions almost perfectly, or as close as can be achieved through modern technology and processes.
2. Short battery life, poor RF connections, bad thermal management, and other non-critical aspects of performance are also make-or-break parameters when operating in the real world.
3. The explosion in the growth of the electronics marketplace at every level is challenging the industry at every level. From new semiconductor materials to advanced solutions like artificial intelligence, new technologies and approaches are creating new application spaces while rejuvenating old ones. All of this is being driven by the migration to integrate data technology into every aspect of electronics.
4. All of this is creating a disruptive period of demanding growth, which places additional pressure on system designers to ensure the product created is safe, efficient, reliable, and cost-effective (especially that last one).
5. That means design engineers must select the best solutions for every aspect of the systems they are designing, especially the elements involved in monitoring circuit performance. Advanced current-sensing solutions can address these needs in a comprehensive and cost-effective way.
6. When it comes to consumer and medical wearables, advanced personal electronics, and the internet of things, the smaller, more functional, and longer lasting, the better. Similarly, industrial and automotive applications are pushing boundaries to achieve smaller, more efficient, and less thermally-challenging. This can only be achieved by constantly monitoring system performance under all conditions in real time.
EFFICIENCY AND PERFORMANCE
1. When it comes to electronic systems, it is important to distinguish between efficiency and optimum performance. Some focus on efficiency, forgetting that even though a system is very efficient, it may not be cost-effective because it doesn’t respond to the application as needed during periods of challenging operation. Only by real-time monitoring of power usage can one be confident of both during operation.
2. There is no precision without feedback, and it is impossible to compete today without having your product work in as precise a manner as possible. Current sensing can provide the critical performance information an embedded intelligent system needs to manage itself in a non-invasive manner, in that it doesn’t have to become a major infrastructure element in your design.
3. The migration from passive systems to “smart” solutions with intelligent feedback and control has delivered significant operating improvements. In general, power efficiency and motor-drive open-loop current sense accuracy has been highly beneficial to improved operation over the full temperature range. Growing and developing Industry 4.0 needs and processes have moved the goal post to improved performance at temperatures as high as 85°C or 105°C.
4. In the area of advanced solar inverters, systems are achieving higher levels of accuracy over the temperature range. Similarly, applications needing extremely wide dynamic range with very good accuracy and precision will need higher accuracy over temperature, and can implement a single closed-loop current sense system rather than two open-loop current sensors to track lower and higher currents.
THERMAL ISSUES
1. One of the basics in electronics is that power management is thermal management. Power efficiency and thermal performance go hand in hand, as wasted energy from the system is always expressed as heat. If you can improve efficiency, you can reduce the temperature, and your electronics work better and more reliably.
2. Conversely, if your electronics operate poorly, there is more waste heat, and, therefore, more thermal-management, reliability, and safety issues. Optimizing both power and thermal management will significantly improve productivity, cost-effectiveness, safety, and reliability.
3. Inverter, motor drive, power supply, UPS, and external charging stations must be able to operate at an ambient operating temperature range from -40°C to 85°C, often up to 105°C.
4. Even in inverter applications, where the internal maximum temperature is kept relatively low, such power systems are typically specified for 85°C operation, at least to ensure proper operational headroom without derating. Ambient operating temperature requirements for automotive onboard chargers can go up to to 125°C, while motor drives can go up to levels from 105°C to 150°C, depending on the location.
5. Although many systems use fans and other temperature-regulating mechanisms to manage system thermal performance, for systems with rapidly-changing temperatures and performance dynamics, this can be difficult. In addition, external cooling mechanisms take up extra space that could be used for other aspects of the design, consume additional energy, and present their own efficient operation issues.
6. For systems with potentially rapid changing temperature, measuring the system current can be a faster method for predicting and managing the thermal performance of the system. The management controller that is monitoring the actual current level can determine if the current level is rapidly increasing, indicating a potential catastrophic event.
7. Monitoring the current in real-time while the system is operating is a leading indicator of potential out-of-range events and failure conditions, enabling the system to predict potential catastrophic events before they occur, protecting the system and critical components. No matter what the concern, system performance, system reliability, or fault identification of basic safety are situations that must be addressed as early as possible. Current sensing can detect a potential issue, minimizing system downtime and/or preventing catastrophic failure.
TIMING AND PERFORMANCE
1. Synchronization and regulation are important factors to consider in advanced power systems, as power-factor correction (PFC) stages are also time-oriented systems. The output ripple of the circuit must be filtered to avoid current distortion, and the loop frequency is related to the system bandwidth.
2. Think of the PFC stage as a system delivering power from an input voltage, managed by a control signal, so even if the system control loop bandwidth is lower, currents are measured during each power switch cycle, for cycle-by-cycle current. Under ideal conditions, there should be a high multiple of the switching frequency to have a flat gain response, and low phase margins at the switching frequency. Low frequencies can work, with some compromise on gain and phase delays at switching frequency.
3. Although overall control loop bandwidth may be much lower than the switching frequency, the current measurements should be taken at the switching frequency for cycle-by-cycle control. Most Totem pole PFCs are switching at ~65 kHz to 150 kHz, which will require bandwidth of ideally 650 kHz (at least >300 kHz) to 1.5 MHz. This switching frequency is being pushed to 300 kHz in some cases in advance designs and will require ~3-MHz bandwidth (at least 1.5-MHz bandwidth).
4. Power conversion with high currents of up to 1,000 A will nominally switch at levels from less than 1 kHz up to 20 kHz, typically with IGBTs and silicon MOSFETs. Other circuits can switch up to around 40-50 kHz with wideband silicon carbide (SiC)/gallium nitride (GaN) power switches, and further advances in SiC/GaN power stages may move this high-current switching up to 100 kHz eventually, requiring bandwidth from 500 kHz up to 1 MHz.
5. Whatever the application, pay careful attention to the following parameters in designing your power monitoring system:
SELECTION CRITERIA FOR POWER MONITORING SYSTEM
1. Accuracy: Class 1 power meters require current sensors with much better than 1 percent accuracy. The sensor is generally expensive and utilizes costly manufacturing processes. An alternative to using expensive sensor elements is to calibrate the power meter for each single element. Taking into account the specific characteristics of each sensor allows you to use it in its most precise operating mode and to mitigate the variations from one sensor to another.
2. Drift: A sensor's drift defines its ability to sustain a given reading over time independent from the initial system calibration. Some variations in sensor characteristics may be caused by changes in ambient humidity and temperature as well as component aging. Clearly the designer's task is to select a sensor with low-drift consistent with the most cost-effective solution
3. Linearity: We can define linearity as the sensor's ability to retain its characteristics over its full operating range. A high linearity of the analog sensing part is essential to provide accurate measurement over a wide range of primary currents, and especially at low current levels. Several technologies offer good performance over only a limited measuring range, thus limiting their application to rather high or low currents.
4. Phase shift: The accuracy of the true active power or energy calculation is related not only to the accuracy and linearity of the AC current and voltage sensor in terms of amplitude, but also the phase shift that may occur between the measurement of these correlated values. The phase shift should of course be as low as possible.
5. Integration: The sensor's current transformers are essentially self powered, and do not require wiring other than a 2-wire output connection to the main power monitor unit. Many of them provide calibrated standard outputs, allowing easy integration in the power monitoring system. The typical 1- and 5-amp or 333 mV outputs are compatible with most standard power meters on the market.
6. High-accuracy power meters require specific calibration with sensors that are no longer interchangeable. As a consequence, these systems often deliver low-current outputs that are safer than traditional 1- and 5-amp signals. Sensors with current outputs are almost insensitive to interference and are preferable to voltage outputs when long cables are required to connect the sensors to the power meter.
7. Price: The cost of the sensors come into play especially when three accurate current sensors are required for 3-phase power measurement. When considering overall price, also consider installation and maintenance costs. Although more expensive, reliable and easy to install and replace, split-core sensors bring greater cost reduction to the system as a whole.
Source:
https://www.edn.com/current-sensors-and-industry-4-0-what-do-engineers-need-to-know/
https://www.eetimes.com/which-current-sensor-for-power-measurement/?_ga=2.264454031.1697459327.1672210160-2082054220.1670837804
