Why Do Advanced EV Charging Systems Need Precision Current Sensing?
Advanced current sensors have an essential role in charging systems as part of the feedback control-loop function, which enhances the performance, efficiency, and thermal linearity of EV charging systems.
The latest generation of electrical vehicle (EV) charging solutions needs precise and accurate current sensing in order to achieve their best performance. Only by using the appropriate current-sensing methodology can a charging system offer the best accuracy, reliability, and safety.
The growing adoption rate of electric vehicles of all types has focused even more attention on vehicle battery systems, as the focus shifts from EV range to charging times. EV charging systems must operate safely and reliably, as issues with a poor implementation can range from inefficient operation to shortened operational lifetimes. Using the correct current-sensing methodology prevents these concerns from impacting the system.
When it comes to the latest generation of EV charging solutions, the power electronics infrastructure is as important as the on-board systems in the vehicle. The greater the adoption level, the more important it is to have a functional charging infrastructure in place. While charging stations are currently being deployed on highways and in cities, the ability to charge at home is becoming a major aspect of the EV charging market.
The more that charging infrastructure expands into our businesses, public areas, and homes, the greater the need for safety and reliability in EV charging systems. A failure of any aspect of the power electronics can result in conditions that present a significant fire hazard, especially in a home-based system. However, the same current-sensing solutions that improve EV performance also address issues of safety and reliability.
Range and speed
While the latest power electronics and conversion solutions are eliminating driving-range anxiety and battery-life fears, which also increases consumer adoption, it is also important to improve the efficiency, safety, and performance of the power conversion system in a cost-effective manner. When it comes to EV charging performance, issues include ensuring tight power-factor correction (PFC), measuring the current, and optimizing conversion, while ensuring proper thermal management. Each of these facets leverages the other in a power conversion system.
When it comes to the performance and efficiency of an EV charging solution, current measurement helps manage thermal performance. A serious consideration, improper heat management, can be both destructive and costly. Properly done, the right current-sensing methodology increases the performance, safety, and cost-effectiveness of power electronics.
Among other advantages, advanced current measurement solutions also provide early fault detection and real-time performance information. The ability to rapidly and accurately detect an overcurrent condition or other loss of performance also enables the system to predict and address things like potential circuit problems like conditions that can create thermal issues.
When it comes to the extreme power levels and loading conditions present in EV charging systems, it is not only important to protect against obvious dangers like ground faults and short-circuits, but it is also critical to be able to monitor the system’s real-time performance. Advanced current sensors have an essential role in charging systems as part of the feedback control-loop function, which enhances the performance, efficiency, and thermal linearity of EV charging systems.
Types of current sensors
A simple shunt-based current sensing solution measures the voltage drop to determine the current flowing through the circuit. Although it can offer decent dynamic performance and linearity, a resistive detector has limitations at high and low currents. Active compensation can help address this issue, but at the high currents an EV charging system presents, the resistive power dissipation in the shunt itself can become a thermal issue. In addition, this kind of sensor is contact-based, which increases the system complexity as well as the potential for failure.
A more sophisticated solution than a shunt-based solution, a Hall sensor is isolated, but lacks accuracy and bandwidth compared to other solutions. Based on the circuit topology and performance desired, it can be deployed in potentially compact configurations. A solution using a current transformer is isolated and can be more accurate depending on the circuit topology, but its size and weight are an issue. Such a solution is less than suitable for a cost-effective compact automotive charging system, especially in homes where space and bulk are issues.
An advanced embedded solution based on AMR-based current sensors provides galvanic isolation, with no power dissipation and enables a fast and accurate readout while correcting offsets via active feedback loops to adjust gain parameters and actively compensate for sensor offset. An integrated current-sensing solution in advanced power systems offers both performance advantages in addition to significant footprint savings over other available solutions. The size of a non-integrated solution using an op-amp and comparator will be larger than a single-package solution that presents a footprint measuring dozens of millimeters in size.
In the area of advanced over-and undercurrent protection, the needed speed and power level of EV battery charging systems demand the best solutions. Traditional fuses and circuit breakers are often inadequate, as the faster switching speeds and higher power levels of the latest EV charging systems demand real-time monitoring of every critical aspect.
EV manufacturers are also addressing these advanced charging demands by increasing the working voltage, which is currently as high as 800V. Providing the same amount of power with less current, these higher-voltage systems can result in a lower overall vehicle weight, as they have a lighter charging cable to carry. An EV with an 800V charging architecture and a charging station that can handle high power levels drops the charging time significantly. While 400V EVs can be charged at around 150 kW, for example, an 800V charger can recharge at a rate of 350 kW.
In order to present as cost-effective a solution as possible, home-based systems are usually deployed with the highest possible power densities. This means the latest EV chargers must have advanced current measurement for early fault detection and performance information in real time. Advanced charging systems must always be on the alert for out-of-range current conditions and other performance challenges, alerting the system to potential thermal and performance issues.
EV power issues involve more than managing the battery and charging systems.
The rest of the system is just as important in an EV’s (and in many industrial motor-drive applications as well), like the traction inverter and the rest of the drivetrain. Using advanced current sensing as a method to obtain additional vehicle performance information like the real-time battery discharge rate is another advantage for the battery management system, further increasing EV safety and reliability.
Avoiding risks, improving performance
Many next-gen chargers are being driven at the edges of their performance envelopes, especially in compact home-based systems, underscoring the need for early fault detection and real-time performance information. In order to predict and address potentially dangerous issues, hard-driven EV battery-charging systems must be able to immediately detect out-of-range current conditions or other loss of performance.
These dangers range from typical ground faults and short-circuits to those that come from operating at extreme power levels and at loading conditions beyond the system’s capability to support. Advanced current sensing in charging systems also performs the initial part of the feedback control-loop function, regulating the performance, efficiency, and thermal linearity of the power circuits in inverters.
Current measurement is a key aspect of over-and undercurrent protection. At the speeds and power levels of EV charging systems, traditional fuses and circuit breakers aren’t up to the job, unless used to prevent catastrophic failure in extreme situations. Advanced current sensing enables intelligent fault management that can better address creeping performance issues like user error and minor damage to cables and connectors.
Smart power methodologies using advanced current sensors protect both the circuit and the battery or batteries involved against abuse (intended or unintended), while optimizing performance, reliability, and safety. In the case of powerful and dense cells based on Lithium Iron Phosphate (LFP) or Lithium-titanate (LTO), it is important while charging to determine the battery’s State of Charge (SoC), State of Health (SoH), and State of Function (SoF). Only by closely monitoring those aspects can one confirm a battery’s complete functional status.
Advanced sensing solutions that protect from overcurrent conditions and improve safety, like those from Aceinna, are well suited for the task due to their very fast response time and large current measurement range. Such isolated devices work in both the high and low sides of a circuit, and their integrated nature reduces design complexity when compared to a shunt-plus-amplifier solution. For example, on the high side of the power circuit, Aceinna current sensors can detect ground faults of the phase current (possibly due to wrong wiring, aging, etc.), thereby protecting the entire circuit.
Power and heat are inextricably linked when it comes to system safety. It is important to design a circuit to be as efficient as possible to reduce waste heat. The power electronics must also address any external heat the system encounters that adds to the thermal load, meaning any power electronics design must also be optimized for thermal conditions generated from within or without.
The heat generated from the power management circuitry is not properly handled, it can impact the performance of any electronics in the vicinity, especially sensitive analog components like sensors, forcing these products to work at much higher operational temperatures than they are normally exposed to. Advanced current sensing methodologies can also help monitor these thermal issues in a circuit.
By reducing EV charging instability and the risk of system failure, among other circuit issues, advanced current-sensing methodologies also improve a system’s performance. Leveraging Anisotropic Magneto-Resistive (AMR) technology, Acienna’s current sensors are precise and contactless, which, in addition to optimizing performance, also reduces the complexity of the design compared to using a shunt-plus-isolated-amplifier solution.
The power factor of a circuit is a big part of the power quality equation and is essential for efficient operation in advanced EV chargers. The power factor correction (PFC) in a circuit improves the power factor ratio and power quality, increases the device’s energy efficiency, and also reduces grid stress and electricity costs. Improving the power factor, with the ideal compensation applied at the point of load in real time, can leverage advanced current sensing on the low-voltage side to improve the power available.
Driving forward
The EV charging ecosystem is still developing as we deploy it, and the final configuration is still a long way ahead of us. Using next-generation circuit-management solutions empowered by Acienna’s current-sensing solutions can help you navigate it safely, without sacrificing performance, in a cost-effective manner. Efficiency, reliability, and performance are all intertwined, and the proper current-sensing solution will serve all aspects of an EV charging system.
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