Technical Article

# How to Empower Automotive DC Fast-Charging with Advanced Current Sensing

November 26, 2021 by Michael DiGangi, ACEINNA

## Although range anxiety is disappearing from the short list of objections to EV adoption, it has been replaced by recharging speed angst. For the demanding consumer marketplace, fast DC charging systems are emerging as the preferable way to go.

While the adoption curve for electric vehicles (EVs) is constantly changing for the better, the automotive industry is dealing with the remaining driving-range anxiety and battery-life fear.

Through improved EV electronics such as power management and motor control, along with increased energy storage densities, the automotive industry has gone far to alleviate range and capacity concerns. There are still reasonable concerns behind EV charging times. This is why it is critical that the EV industry fields advanced fast battery-charging systems and make them available to the public.

Faster charging will increase EV adoption, as it directly addresses perceived user aggravations. It is also financially lucrative, as the EV charging market is growing rapidly, with installations expected to surpass 9 million units by 2025. In 2019 the EV charger market was approximately $4 billion and should reach$25.5 billion by 2027 (https://www.alliedmarketresearch.com/). The Electric Vehicle Charging Station market worldwide is projected to grow to 30,758,000 units by 2027. There are several methodologies available when it comes to charging EVs. Highway and city charging stations are currently being deployed, but the ability to charge at home is a major market trend. Most individual passenger cars remain parked overnight, making home charging easier and often cheaper than charging elsewhere. However, even home charging situations can demand short daytime recharging, if only for other family member vehicles and visitors.

## Charging types

The most common wall-plug chargers are known as Level 1 and Level 2 systems. Since EV batteries are charged with a DC current, a conversion stage is needed. Using an onboard AC charger is more affordable in some deployments because in-vehicle power conversion stages replace any needed in-house charging systems. However, in-car conversion circuitry limits power capacity and charging time (see figure 1).

##### Figure 1. Various levels of AC and DC Electric vehicle Charging Systems. Image used courtesy of Bodo’s Power Systems

Level 3 DC fast charging is available in higher voltages and can charge some plug-in electric vehicles with up to 800 volts, allowing for very rapid charging. This solution is best for residential and business buildings as well as facilities due to cost. For most household deployments, high-power Level 2 systems, currently operating at levels of up to 50 Amps, are turning out to be the best mainstream solution.

In-home DC fast-charging systems are becoming a significant part of the growing electrical mobility infrastructure. When developing consumer-oriented capital goods, longevity and reliability compete with cost-effectiveness in the buying decision. Cost-effectively improving the efficiency, safety, and performance of the power conversion system increases consumer acceptance. The four aspects of a power conversion system involve measuring the current, ensuring tight power-factor correction, frequency management, and addressing thermal issues. Each leverages one another to impact the overall performance of the system.

## Current measurement

Beyond determining power output, current measurement can also help manage thermal performance. Poor thermal management is destructive and costly, and when properly done can significantly increase performance, safety, and cost-effectiveness. Current measurement provides, among other things, early fault detection and real-time performance information. Many power systems require an indication of an out-of-range current condition, or an overcurrent condition, or other loss of performance, to predict and address potential thermal issues. Dangers to power electronics’ performance, and thereby system thermal issues, range from ground faults and short-circuits to operating at extreme power levels and at loading conditions beyond the system’s capability to support. Current sensors in charging systems are deployed in each converter module in a charging system, as part of the feedback control loop function regulating the performance, efficiency, and thermal linearity of the power systems in inverters.

When it comes to current-sensing in power systems, an integrated sensing solution offers significant footprint savings over board-assembled solutions using an op-amp and comparator. The size of a non-integrated implementation will vary depending on the actual components chosen, but it will be larger than a single-package solution. If we use a traditional component package size for devices of this type, around 2~3 mm, this leads to solution footprints dozens of millimeters in size.

## Overcurrent detection

By definition, current measurement is a key aspect of over-and undercurrent protection against damage in electronic systems. At the speeds, power levels, and always-on aspect of modern systems, fuses are no longer adequate in any manner for advanced power products except to prevent catastrophic failure. Using a fuse for protection doesn’t give you any information on the actual performance of the power system beyond cutting the power in an overcurrent situation. Using a current sensor, an overcurrent detection response can be optimized for a given application. Circuit protection and safety of the overall system is paramount, and current-sensing solutions like ACEINNA’s are well suited for overcurrent detection, due to their very fast response and large current measurement range. Being isolated, they can be used on both the high and low sides of the circuit.

Integration of aspects such as isolation, along with the core Anisotropic Magneto-Resistive (AMR) technology, creates sensors that are precise and contactless. This manner of current sensing optimizes performance and enables temperature correction, reducing the complexity of the customer design compared to a shunt plus isolated amplifier solution. Additionally, by using a device such as the ACEINNA current sensor on the high side, the ground fault of the phase current could be detected (possibly due to wrong wiring, aging, etc.), and the overall system could be protected. Power quality is essential for efficient operation, and the power factor is a big part of it. Power factor measures the efficiency of incoming power used and is a ratio of active to apparent power. If you have a bad power factor, less than 95% for example, it results in more current needed to do the same work. Power factor correction (PFC) improves that ratio and the power quality. PFC reduces grid stress, increases device energy efficiency, and reduces electricity costs while reducing instability and risk of system failure.

Producing reactive energy in opposition to the energy absorbed by loads such as battery chargers, close to the load, improves the power factor, with the ideal compensation applied at the point of load, at the needed level in real time. Using a current sensor on PFC equipment on the low voltage side improves the power available. When it comes to harmonic distortion, PFC is necessary for the AC/DC inverter front end, and most of the time, isolation between the primary and secondary sides of the AC/DC front end module is required, ACEINNA’s current sensors not only simplify the overall system design but reduce the cost of implementation.

## Switching frequency

With the increasing demand for higher performance, CPUs, DSPs, and other such devices are growing more power-hungry. Increasing the regulator frequency reduces the size and board footprint requirements of the power circuit involved while increasing power density. However, as frequency increases, so do switching losses, mostly due to high-side losses during turn on, as well as body-diode conduction losses. These forces limit the switching frequency of conventional converters and regulators.

Current measurement in advanced fast-switching circuits is required to track the currents in real-time for the highest efficiency possible. Intelligent current measurement is also required in AI and machine learning to create a control algorithm for better performance. ACEINNA’s high accuracy and high bandwidth current solutions increase the efficiency of the system while simplifying the current control design, due to its high phase margin.

## Driving forward

The market for fast recharging systems to accelerate EV adoption and market viability, requires advanced, efficient, and cost-effective charging solutions. Fast DC charging is one of the more preferable forms of EV replenishment, and using advanced current sensing to optimize such systems, will ensure product success in the rapidly growing EV charging marketplace.