Protecting High-voltage Circuits

Yazaki readies a new solution for arc suppression in circuits of 48V or more.

June 1, 2019

Lindsay Brooke

As OEMs develop their next-generation electrical architectures aimed at new hybrid, EV and autonomous vehicles, engineers are focused on delivering systems that are even more robust and “fail-safe” than those used today. Handling more power safely is a given, experts say, as more power-gobbling heated seats, electric turbos, active suspensions, lidars, on-board data processors and other safety sensors are added.

“The industry is now undergoing a fundamental change in how much electrical power is being used,” observed Eric Varton, chief engineer of advance development for Yazaki North America Core Engineering. He noted that the typical 12V vehicle architecture launched in the early 1960s is only capable of deliveing around 2 kW power. In an autonomous vehicle, the autonomous Drive module alone could consume 2 kW.

“I believe forty-eight volt systems with up to 20 kW of power will ultimately replace 12 volt systems,” Varton asserted, and he predicts 350V-, 400V-, 600V-systems on full hybrids—with larger vehicles and trucks moving to 800V to 1000V. “Component draw will increase; consumers will see value in features like window defrosters that can defrost a windshield in 30 seconds, instead of two minutes,” he explained. “They’ll pay for heated wipers, and for seats that heat up even faster.”

As vehicle architectures move to higher voltages, enter the need for advanced current-sensing and DC arc suppression. New examples of both technologies have exited the proof-of-concept stage and are nearing production at Yazaki. The value of arc suppression is to protect the electrical circuits and their connectors and devices, in the event of an energized disconnect of various causes—from operator error (loose-not-attached connections) during vehicle assembly, to road-induced vibration, to service-tech diagnostic mistakes. Arc suppression also offers the benefit of extending the life of high-current switches or relays, Varton said.

Solid-state solution

Small but effective: Yazaki’s arc suppression device is compact and cost-effective, the company says. (Image credit: YAZAKI NORTH AMERICA)

An arc is a discharge of electrical energy between two electrodes in a live circuit. As the energy released in an arc event increases, so does the amount of destruction it can potentially inflict on system components. Arcing can be characterized as Serial — a hot disconnect, for example — and Parallel, such as a short circuit. It’s an issue on power systems over 42V as ionization of the air in the gap between wire terminals is more easily achieved at higher voltages.

Arc intensity is directly related to voltage, current, and the rate of separation of the contact terminals. Arc event likelihood increases as voltage and current increase in a circuit. The slower the terminal separation, the more likely an arc will occur, explained Varton.

“Arcing creates damage — and potentially fire,” he asserted, then showed video clips of two arcing events demonstrated in the Yazaki laboratory. The first demo, conducted with a 48-V, 11-amp; circuit — the load of a typical heated seat — shows a flash of near-MIG-weld intensity. The second demo was of a 500-V, 2-amp circuit — the arc erupted into fire in about four seconds.

According to Varton, DC arcs create frequency harmonics that can be detected by DSP (digital signal processing) hardware. He said that while DSP technology works well at a system level for detection, it also requires costly hardware to implement. And in a serial-arc event, DSP response times typically are too slow to prevent circuit damage, he stated. Sometimes, the circuit is shut down only after the arc event is completed.

Scaling arc-suppression solutions up to 500V is important to meet upcoming hybrid and EV requirements, noted Yazaki’s Eric Varton. (Image credit: LINDSAY BROOKE)

Short circuits can be detected with a fuse or a smart FET to shut down the loads, but they come with issues, Varton argues. (Field-effect transistors are electronic devices that use an electric field to control current flow.)

“Smart FETs are really great except they require a microcontroller and are expensive — and you have to really characterize your loads well,” Varton noted. Yazaki’s DC arc suppression device—resembling an insurance dongle but physically smaller — is solid state and scalable up to 500V. When wired in parallel into the circuit, it senses the change in voltage, opening a semiconductor switch that reroutes the electrical energy instead of it traveling across the pins.

“Our little unit — it’s just a small board in a box—fits in a standard ISO relay slot and can protect up to two circuits,” Varton said, then asked rhetorically, “In the event of a live disconnect or short circuit, what do you do — replace a high-cost component because a connector was melted? Or install a device that is far less expensive to protect that high-cost item?”

Hi-res in a small range

Current sensors capable of higher resolution are also in advanced development at Yazaki, revealed David Scheffler, Yazaki North America’s VP engineering. He explained that vehicle voltages of 48V and above are driving the need for higher current-resolution measurement. This is particularly vital in the lower current range in order to precisely calculate battery state of charge and state of health (SOC and SOH). In lower resolution technologies, measurement errors can accumulate over time to skew SOC and SOH readings.

“Current sensing is a patented technology here,” Scheffler told Automotive Engineering. “Our new approach senses resonance using a Hall Effect sensor that’s more accurate than the sensors we use to certify our parts for the OEMs. In fact, we’re identifying applications beyond automotive for this.”

Raising system voltage from 12V to 48V reduces current by a factor of four—“still managing a lot of power, but with a small current,” Varton noted. “So, you need better resolution in this very small range,” better than shunt - and magnetic-based solutions can deliver, he claims. “When you have offset in this small range you don’t have enough resolution to get an accurate result for battery and SOC management.”

In Yazaki’s Resonant Current Sensor that’s nearing production, offset and gain errors are canceled out, Varton said. Sensing gain is independent from the operating voltage and temperature variations. The RCS will be offered in form factors from +/-350A to +/- 1200A, with 9V-16V operating voltage. Minimum measurement range is ± 1200A @ 13.5V (± 1000A @ 9V). Both differential and single-end signal interfaces are available, according to Varton.