How to improve the efficiency of electric vehicle onboard power

Infinitum chose to produce industrial motors, a market with huge scale. Infinitum's solution (right) takes up less space than traditional wound motors. (Infinitum)

The development of electric powertrains is advancing at a breakneck pace as OEMs, suppliers and startups work to optimize existing technologies while pioneering new ones.

Current drive motors and electronics are already very efficient, but automakers are still innovating a lot to further improve the efficiency of electric vehicle onboard power. Here are some of the latest developments:

Infinitum：

Continue to launch newer, lighter motors

Infinitum removed all the iron and copper windings from the stator core of the motor and replaced them with a printed circuit board (PCB) stator with etched copper conductors, resulting in a smaller and lighter motor than traditional axial flux motors. The design eliminates all core losses in the stator, such as torque ripple, cogging, stator hysteresis and eddy currents, which "significantly improves efficiency." The motor is smaller, quieter, more efficient, and has higher efficiency across the entire motor operating curve.

An exploded view of Infinitum's Aircore Mobility motor. (Infinitum)

Initially, Infinitum sought to address the inefficiencies of HVAC motors and is currently focusing on the industrial market.

Infinium delivers coolant directly to the center of the stator, where it is centrifugally spun outward, cooling the stator and other parts, until it hits the housing and drains into the sump, where it is recirculated. (Infinium)

At CES 2023, Infinitum announced its latest development - a hollow core motor with a PCB stator, whose liquid cooling system can deliver coolant directly to the motor heat source. The motor injects coolant into the hollow shaft so that it is in direct contact with the stator, and the excellent heat dissipation makes the power density four to five times higher than that of traditional radial flux motors. Most cooling methods used in radial and axial flux motors can only inject coolant into the jacket around the motor. Infinitum inputs coolant into the center of the stator, and centrifugal force can push the liquid into the outer jacket, drain it into the liquid tank, and recirculate it, so that the motor with 150 kW (201 hp) continuous power and 300 kW (402 hp) peak power can run at 95% efficiency at 7500 rpm.

The company's head said that hollow motors using silicon carbide MOSFETs can achieve higher-speed switching. The motor can be updated OTA, and its size can be determined according to the application or whether to use multiple smaller motors instead of a large motor.

The air-core motor is designed for cyclic use. The etched copper laminates use an off-the-shelf FR4 glass epoxy as the insulation material. The company says this makes the standard stator 10 times more reliable. How is this done? Schuler explains: "All of our copper laminates and insulation materials have equal coefficients of thermal expansion and will heat and cool repeatedly at the same rate without mechanical interference and therefore failure."

Schaeffler:

System efficiency

Schaeffler is looking to improve the efficiency of permanent magnet motors by adjusting the position of the magnets, and is turning its attention to externally excited motors without magnets. Motors without magnets are generally less efficient, but Schaeffler engineers say they can develop externally excited motors with "equal" efficiency to permanent magnet motors.

Schaeffler's 4in1 e-axle seeks to maximize system integration by integrating traction motor, transmission, power electronics and thermal management system (which may include heat pump). (Schaeffler)

The company's recently revealed solution is the "4in1 e-axle" - based on the traction motor, transmission and power electronics in its three-in-one system, a thermal management system has been added to greatly improve efficiency. Schaeffler claims that the silicon carbide power electronics developed in collaboration between departments can provide more than 99% efficiency. Schaeffler's new 4in1 e-axle can integrate the shift mechanism of the second-speed gearbox. Some people think that this is a worthwhile addition for the larger and more inertial vehicles favored by the US market. In addition, Schaeffler also provides corresponding decoupling units.

ZF:

The entire powertrain

In November 2022, ZF launched a new electric drive powertrain that combines many advantages. Like other designs focused on adapting to 400V or 800V architectures, its flexibility comes from controller chips and inverters with separate power switches. The company claims that this architecture requires fewer components than today's power modules. The system has a minimum shaft power of 100 kW (134 hp) and a maximum of 300 kW. Related reading: ZF launches a full set of electric drive systems to help OEMs shorten development time.

ZF's electric motors use braided windings to increase power density and reduce raw material use. (ZF)

ZF's new electric drive system uses braided winding technology to increase power density. Roland Hintringer, head of the motor product line, said: "The hairpin winding introduced five to seven years ago is the most advanced technology today, but it requires hundreds of laser welding points." He also said that ZF's braiding is formed in the same operation step, saving both time and space. Its winding head is 15 mm, while the hairpin winding is 28 mm. Only 24 welding points are required, and the braiding method also saves 10% of the raw materials.

At the same time, ZF is also developing liquid cooling technology like Infinitum. In addition to water-cooling the motor housing, cooling oil is pumped around the housing and into the slots of the braided windings themselves. Compared with existing technologies, the peak performance of this technology is improved by 85%, the power is increased by 50%, and the amount of rare earths used is only 1% of the current level.

eLeap Power：

Inverter that doesn't require an onboard charger debuts at CES

Canadian company eLeap Power says its inverter technology uses the existing motor windings in the drive motor, eliminating the need for an onboard charger and transformer. eLeap says this invention has many benefits:

800v charging speed, but compatible with 400v systems.

By eliminating the onboard charger, the vehicle is 30-40 kg (66-88 lb) lighter and has a longer range.

Compatible with almost all current electric vehicle powertrain architectures, and at a low cost, because it can adapt to the 800V architecture while using the cheaper, lower voltage switching elements available today.

It is fully bi-directional in both AC and DC. This allows the direct charging of vehicle batteries using renewable sources such as wind and solar, while also allowing the vehicle to “recover energy” during peak demand.

The inverter uses a split-battery or dual-battery system to achieve higher reliability. If one part of the system fails, the vehicle is still usable.

eLeap Power's integrated inverter uses the motor's windings (the motor doesn't move) to replace the onboard charger and slow down charging. (eLeap Power)

The relevant person in charge of eLeap believes that the system is smarter and more powerful. It means that the vehicle can charge faster and travel farther after charging. It also saves costs and is more environmentally friendly. The core of the eLeap system is that it uses the magnetic field and windings in the motor in combination with software to generate high-speed current to charge the battery. In addition to removing the on-board charger, vehicles such as Lucid Air, which currently use 400v/800v boost converters, no longer need to use converters. He said: "We are able to gain huge cost advantages because we use motors in charging operations. Therefore, inductors and transformers are usually not required." He said: "The charging process is static, the motor does not rotate, and there is no vibration."

eLeap says it solves the problems other companies encounter when trying to integrate the inverter by splitting the battery, essentially putting the inverter somewhere in the middle of the process. (eLeap Power)