Effective current sensing aids automotive fast DC charging - Embedded.com

Effective current sensing aids automotive fast DC charging

For the demanding consumer EV marketplace, fast DC charging systems based on the latest wide-bandgap semiconductors are emerging as the preferable way to go.

For the demanding consumer EV marketplace, fast DC charging systems based on the latest wide-bandgap semiconductors are emerging as the preferable way to go.

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.

The adoption curve for electric vehicles (EVs) is constantly changing for the better, as EV performance improves due to advanced power electronics and conversion topologies, which address driving-range anxiety and battery-life fears. These improved EV power management and motor control electronics are mostly due to the advent of next-generation wide-bandgap (WBG) semiconductors, as they have enabled the creation of highly efficient advanced power systems.

These same WBG semiconductors are also energizing (pun intended) the EV charging industry at all levels. As consumer concerns shift from range anxiety to charging speed, WBG-based charging systems are now being fielded in the marketplace to address the need for fast in-home EV charging. These next-generation EV chargers have a significant role in the rate and extent of EV adoption going forward.

Charging forward

The most prevalent type of WBG-based wall-plug chargers are known as Mode 3 (level 2) systems delivering up to 50 kilowatts, a much higher output than earlier level-1 systems, based on legacy technologies, are capable of. A DC-based charger, also known as a level 3 or direct-current fast charging (DCFC) system, operates from 25 kilowatts to over 350 kilowatts, significantly reducing charging times in kiosks and other public locations.

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Charging Stations

Charging Stations

In 15 minutes, a 150 kW DC charger can put 200 km on an EV, and many can get an 80% charge in under an hour using the best DC fast chargers available in the market today. 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.

All that can be done to cost-effectively improve the efficiency, safety, and performance of the power conversion system can only increase acceptance. The three 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.

WBG types

WBG semiconductors currently come in two types, Gallium Nitride (GaN) and Silicon Carbide (SiC). Each has its individual benefits, but both create devices significantly better performing than legacy transistors based on Silicon. Interestingly enough, GaN is well-suited for low-to-medium power applications, while SiC addresses very high voltages and power levels.

GaN is a piezoelectric semiconductor that enables extremely high efficiencies and switching frequencies, enabling not only better performance, but also a reduction in solution footprint due to the ability to reduce the size of the passive components involved. SiC can operate at higher temperatures more efficiently while managing voltages high enough to address even the most demanding EV systems.

In the latest home and public EV chargers, GaN is finding itself more in the control electronics, and SiC is finding itself more in the power conversion stages. This split is blurry at median power levels, as both GaN and SiC can address applications in the hundreds of volts and dozens of amps. This has resulted in a pressure to upgrade all the related components on the board to address the added capabilities of the system.

Current events

In an advanced WBG-based power system, accurate, rapid, and intelligent current measurement is critical. In addition to determining power output, proper current measurement can also help manage thermal performance, as poor thermal management is destructive and costly. Properly done advanced current measurement can significantly increase performance, safety, and cost-effectiveness in advanced WBG-based power circuits.

Most next-gen chargers are being driven at the edges of their performance envelope, and advanced current measurement provides, among other things, early fault detection and real-time performance information. WBG-based power systems require an indication of an out-of-range current condition, or an over-current 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 advanced charging systems are deployed in each of the converter circuits to perform the initial part of the feedback control-loop function which regulates the performance, efficiency, and thermal linearity of the power systems in inverters, especially those based on WBG semiconductors.

When it comes to current-sensing in these power systems, an integrated sensing solution is the only real solution, as it offers not only the needed performance but also 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 WBG-based power systems, traditional fuses are no longer adequate in any manner for these advanced power products except to prevent catastrophic failure. The higher switching speeds and power levels of WBG power systems demand real-time monitoring of every critical aspect of an advanced EV charger.

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, overcurrent detection response can be optimized for any 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 amr sensor and temperature correction, reduces 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.

current sensor

Power quality is essential for efficient operation, especially in these advanced WBG EV chargers, and the power factor is a big part of it. The ratio of active to apparent power, a bad power factor, less than 95% for example, results in more current needed to do the same work. Power factor correction (PFC) improves that ratio and the power quality, 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 in the AC/DC inverter front end, and most of the time, isolation between the primary and secondary side 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

The switching frequency in a power circuit has gone up significantly in WBG-based power systems, especially those based on GaN, demanding higher performance from the magnetics and passive devices. Advanced current sensing addresses this need for better components in the system. In addition, increasing regulator frequency reduces the size and board footprint requirements of a power circuit. However, as frequency increases, so do switching losses, mostly due to high-side losses during turn-on, as well as body-diode conduction losses.

Current measurement in advanced WBG 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, require advanced, efficient, and cost-effective charging solutions based on the latest WBG devices and circuit topologies. In-home fast charging with the latest power systems is one of the more preferable forms of EV replenishment, and using advanced current sensing to optimize such WBG-based systems will ensure product success in the EV charging marketplace.

>> This article was originally published on our sister site, Power Electronics News.

Michael DiGangi has been appointed Executive Vice President and is responsible for ACEINNA’s worldwide sales efforts. He brings with him over 26 years of Power and Analog IC semiconductor sales, business development and marketing experience spanning a number of larger corporations and start ups.

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