ORNL Motor Drive Design Targets Heat and Wear for High-Power Electric Propulsion

ORNL Motor Drive Design Targets Heat and Wear for High-Power Electric Propulsion

The next phase of transport electrification will depend on more than battery capacity and charging speed. Heavy-duty trucks, construction equipment, ships and aircraft need propulsion systems capable of handling sustained high electrical loads without excessive heat, interference or premature component degradation. Improvements within the motor drive could therefore prove as commercially important as advances in battery chemistry.

Researchers at the US Department of Energy’s Oak Ridge National Laboratory have developed a dual-inverter motor drive design intended to reduce two persistent sources of electrical stress in high-power systems. Simulations indicate that the configuration can reduce neutral-point voltage fluctuations by 90% and current stress on capacitors by 43%, without requiring additional power-electronic hardware.

That combination matters because reliability, packaging and lifecycle cost remain major constraints on electrifying demanding transport and industrial applications. A solution achieved through system architecture and motor winding configuration, rather than extra filters or protective components, could give manufacturers another route towards higher power without proportionately increasing weight, cooling requirements and complexity.

Briefing

• ORNL’s design uses two inversely synchronised inverters to cancel neutral-point current and common-mode voltage at system level.
• Simulations showed a 90% reduction in neutral-point voltage fluctuation and a 43% reduction in capacitor current stress.
• The arrangement retains the original inverter hardware, although it requires a change to the motor winding configuration.
• Potential applications include heavy-duty trucks, marine vessels, aircraft and other high-power electric motor drives.
• The results remain simulation-based and will require physical testing, application-specific engineering and validation before commercial deployment.

Tackling an Electrical Problem with System Architecture

An electric motor drive controls the transfer of electrical energy from a battery, fuel cell or other power source to the traction motor. At higher power levels, this apparently straightforward function becomes a demanding exercise in electrical, thermal and mechanical management. Switching devices must control large currents rapidly, while capacitors, insulation, bearings, cables and cooling systems must tolerate the resulting stresses over thousands of operating hours.

The ORNL research addresses neutral-point current and common-mode voltage within a segmented motor drive using dual active neutral-point-clamped, or ANPC, inverters. Neutral-point instability can produce voltage fluctuations and place additional current stress on capacitors. Common-mode voltage can generate unwanted currents and electrical interference, contributing to insulation stress, bearing damage and electromagnetic compatibility problems elsewhere in the system.

Conventional mitigation measures can include filters, additional passive components, specialist grounding arrangements, shielding and changes to inverter control. These measures can be effective, but each may introduce some combination of extra mass, cost, volume, losses and engineering complexity. Such penalties become particularly important in applications where payload, installation space and energy efficiency directly affect commercial performance.

ORNL’s alternative uses two inverters operating in inverse synchronisation. By coordinating their behaviour and reconfiguring the motor windings, unwanted electrical effects generated on one side of the system can be counteracted by those on the other. The underlying principle is cancellation at drive-system level rather than treating each source of electrical stress separately after it has been created.

Existing Hardware Strengthens the Commercial Case

The most commercially significant feature is the absence of additional inverter hardware. Manufacturers are generally cautious about adding components to high-power propulsion systems because every component must be purchased, packaged, cooled, controlled, qualified and maintained. It may also create new failure modes and extend the certification or validation programme.

“This design change requires no additional hardware,” ORNL researcher Gui-Jia Su said. “As systems move toward higher power levels, we need solutions that are scalable and reliable.”

That statement does not mean the design could be introduced through a software update alone. ORNL has also identified a modification to the motor winding configuration as part of the approach. Manufacturers would consequently need to assess compatibility with their motor architecture, insulation system, control strategy, production processes and safety requirements.

Nevertheless, the ability to retain the principal power-electronic hardware could make the concept attractive during the development of new electric powertrains. It may allow engineering teams to extract better electrical performance from a dual-inverter arrangement without adding filters or increasing the rating of selected components solely to accommodate avoidable stress.

The research was presented in the paper Inverse Segmented Motor Drive Using Dual ANPC Inverters for Common-Mode Voltage and Neutral-Point Current Cancellation. The work, led by Sangwhee Lee with Vandana Rallabandi, Gui-Jia Su, Shajjad Chowdhury and Burak Ozpineci, was recognised at the 2025 IEEE Transportation Electrification Conference and Electric Aircraft Technologies Symposium. It was developed under the US Department of Energy’s Vehicle Technologies Office.

Capacitor Stress Has Consequences Beyond the Inverter

The reported 43% reduction in capacitor current stress is especially relevant to equipment manufacturers. Capacitors are critical to voltage stability and energy management within an inverter, but their performance and service life are sensitive to current ripple and temperature. Reducing electrical stress can lower internal heating and may create opportunities to improve durability or reconsider component sizing.

Those potential benefits must be demonstrated through hardware testing before they can be quantified. A reduction observed in simulation does not automatically translate into a corresponding increase in service life, because real-world durability also depends on ambient temperature, vibration, contamination, duty cycles, cooling performance, manufacturing tolerances and component selection.

The result is still significant as an engineering indicator. Capacitors can influence inverter size, weight, cost and maintenance strategy, particularly in systems designed for sustained high-output operation. If subsequent testing confirms that the architecture reduces stress across representative duty cycles, designers could gain more flexibility when balancing power density against durability.

Lower neutral-point voltage fluctuation could also simplify voltage balancing within the inverter. More stable operation reduces the need for components and controls to accommodate large deviations, supporting the wider objective of producing compact propulsion packages that can operate reliably under highly variable loads.

A Better Fit for Heavy-Duty Duty Cycles

Passenger vehicles provided the first major market for modern electric traction, but heavy-duty machinery presents a markedly different engineering challenge. A road car may experience high power during acceleration and then operate at a modest load. A haul truck, wheel loader, excavator, marine propulsion unit or aircraft powertrain can encounter repeated or sustained demand, often in hot, dusty, wet or vibration-intensive environments.

These operating conditions magnify the consequences of electrical losses. Heat that cannot be avoided must be removed, requiring cooling equipment, pumps, radiators, coolant and control systems. Those additions occupy space, consume energy and increase the number of parts requiring inspection or maintenance.

Construction equipment also places a high commercial value on uptime. An inverter-related failure can immobilise a machine that is supporting an entire production sequence, from quarry extraction and material handling to earthmoving and paving. Reliability gains therefore have implications extending beyond the affected machine to labour utilisation, project schedules and fleet productivity.

The ORNL design does not remove the need for robust thermal management, nor does it establish a direct route to a specific production machine. Its relevance lies in reducing electrical stresses at source. That principle could complement improvements in semiconductor materials, motor cooling, insulation, control software and integrated electric drive design.

Marine and Aviation Applications Raise the Stakes

Marine propulsion systems illustrate the value of reducing component count and thermal burden. Electric and hybrid vessels must accommodate motors, power electronics, energy storage and cooling equipment within constrained machinery spaces. Equipment must also withstand vibration, moisture, salt exposure and long operating periods while remaining accessible for inspection and repair.

An architecture capable of reducing common-mode effects without adding separate mitigation hardware could support more compact installations. However, marine adoption would depend on validation against the relevant classification, redundancy, fault-tolerance and environmental requirements. Vessel designers would also need to consider how a dual-inverter arrangement interacts with onboard generation, batteries, propulsion controls and auxiliary electrical systems.

Aircraft create an even more demanding balance between power, mass and reliability. Every additional component carries a weight penalty, while any change to a propulsion system faces extensive verification and certification. Common-mode voltage and electromagnetic interference are particularly important where propulsion electronics operate near communication, navigation and flight-control systems.

For aviation, the absence of additional hardware is therefore strategically relevant, but it does not shorten the underlying certification challenge. The technology would have to demonstrate predictable behaviour under normal operation, inverter faults, winding faults, thermal extremes and degraded operating conditions. Its strongest near-term role may be as an architecture considered during the design of new propulsion platforms rather than as a retrofit for certified aircraft.

Implications for Construction Equipment Manufacturers

Off-highway equipment manufacturers are adopting a mixture of battery-electric, cable-electric, hybrid and fuel-cell-electric architectures. Although their energy sources differ, each depends on electric drives capable of converting and controlling substantial amounts of power. Motor-drive improvements can therefore benefit several electrification pathways rather than one particular battery configuration.

A dual-inverter design may be suited to larger traction motors and electrically driven hydraulic systems where high power and controllability are required. Electric drives are already being considered for traction, slewing, lifting, pumping, ventilation and processing equipment. Reducing electrical stress could support greater integration of these functions without allowing reliability or cooling requirements to undermine the operational case.

Procurement teams will ultimately judge electric machinery on total cost of ownership rather than laboratory performance alone. Energy consumption, availability, component replacement intervals, residual value and access to technical support all influence the calculation. Technologies that improve durability without adding material content could strengthen that business case if their performance is confirmed at machine level.

Suppliers may also benefit from design commonality. If a scalable architecture can be applied across several power ratings or vehicle platforms, manufacturers could reduce the need for highly bespoke mitigation systems. The extent of that opportunity will depend on whether the winding and control requirements can be integrated economically into different motor families.

From Simulation to Industrial Validation

The reported figures come from simulations, making them evidence of technical potential rather than proof of commercial readiness. Physical prototypes must establish whether the predicted cancellation remains effective when exposed to switching delays, semiconductor variation, sensor error, temperature changes, motor tolerances and dynamic load conditions.

Testing will also need to measure more than neutral-point voltage and capacitor current. Engineers will want data covering efficiency, harmonic distortion, electromagnetic emissions, bearing currents, insulation stress, acoustic behaviour, cooling demand and performance under partial failure. A system that performs well at nominal conditions must also remain safe and controllable when one inverter, sensor or winding segment behaves unexpectedly.

Integration is likely to be as important as the inverter concept itself. The motor winding arrangement, control algorithms, power source, cabling and mechanical package must be engineered as one propulsion system. This favours collaboration between motor manufacturers, inverter suppliers, vehicle OEMs, research organisations and certification bodies.

ORNL’s National Transportation Research Center is positioned around early-stage transport research and development, including power electronics and electric drives. Moving the concept towards application could involve laboratory prototypes followed by dynamometer testing, representative duty-cycle trials and, eventually, installation in a demonstrator vehicle or vessel.

Designing Reliability into Electrification

High-power electrification will not be secured through a single improvement. Its industrial progress will come from a series of engineering measures that reduce losses, control temperature, increase power density and extend component life while keeping systems manufacturable and serviceable.

ORNL’s work is notable because it treats electrical stress as a system-design problem. Coordinating two inverters and the motor windings to cancel undesirable effects offers a different approach from adding hardware around an established architecture. That could help manufacturers contain the cost and packaging penalties that often accompany movement into higher power classes.

The research is still at a stage where careful qualification matters more than broad claims. Even so, the simulation results provide a credible basis for prototype development. If validated under representative loads, inverse-synchronised dual-inverter drives could become part of the engineering toolkit used to electrify the largest, hardest-working transport and industrial machines.

Key Industry Questions

1. What is the main purpose of ORNL’s motor drive design? The design seeks to reduce neutral-point current and common-mode voltage in high-power electric motor drives. These effects can contribute to voltage instability, capacitor heating, electrical interference, insulation stress and premature wear. ORNL’s system coordinates two ANPC inverters in inverse synchronisation and uses a modified motor winding configuration so that unwanted electrical effects counteract one another. The objective is to improve drive performance and durability without installing extra filters or other inverter hardware. This could be useful in applications where power density, cooling, component life and equipment availability are important design constraints.
2. Does the ORNL design require completely new inverter hardware? ORNL states that the design requires no additional hardware and retains the original dual-inverter arrangement. However, it is not simply a software-only modification. The research describes a change to the motor winding configuration, alongside the inverse synchronisation of the two inverters. Commercial implementation would therefore need to be incorporated into the motor and drive-system design. Existing platforms may require significant engineering work if their motors are not compatible with the required winding arrangement. The strongest initial opportunities are likely to be new propulsion systems where the motor, inverters, controls and cooling package can be developed together.
3. Why is common-mode voltage a concern in electric machinery? Common-mode voltage is an unwanted voltage shared between electrical conductors and a reference such as the chassis or ground. In motor-drive systems it can produce leakage currents, electromagnetic interference and currents through motor bearings. Over time, these effects may contribute to bearing surface damage, insulation degradation or interference with nearby electronic systems. The severity depends on the inverter, switching strategy, motor, cabling, grounding and operating environment. Heavy-duty machinery, vessels and aircraft contain numerous sensors and control systems, making electromagnetic compatibility and long-term component protection important parts of propulsion-system engineering.
4. What does a 43% reduction in capacitor current stress mean operationally? Lower capacitor current stress should reduce one source of internal heating and electrical loading. In principle, this could support longer component life, improved reliability or greater flexibility in capacitor sizing and cooling. It does not establish that capacitor life will increase by 43%, as durability also depends on temperature, voltage, vibration, duty cycle, component quality and installation conditions. The result is currently based on simulation, so physical testing is needed to establish its effect under real operating loads. For fleet operators, the eventual value would come from fewer failures, longer service intervals or more compact drive systems.
5. Could this technology be applied to electric construction equipment? Potentially, particularly in large machines using high-power traction motors or electrically driven hydraulic and auxiliary systems. Construction equipment operates under variable loads, vibration, dust, heat and long working cycles, placing considerable demands on power electronics. A drive architecture that reduces electrical stress without adding components could improve packaging and reliability. Adoption would still require machine-specific development, including shock and vibration testing, environmental sealing, cooling analysis and validation against realistic duty cycles. It is therefore better understood as an enabling motor-drive architecture than as a product ready for immediate installation in existing equipment.
6. Why are dual-inverter systems useful at higher power levels? Dual-inverter systems can distribute power conversion duties and provide greater control over motor windings than a conventional single-inverter arrangement. Depending on the architecture, they may support higher voltage utilisation, segmented windings and fault-management options. ORNL’s concept uses the relationship between the two inverters to cancel neutral-point current and common-mode voltage. This system-level interaction is central to the design. Dual inverters also introduce additional control and integration requirements, so their benefits must be weighed against software complexity, packaging, safety architecture and the behaviour of the system if one inverter becomes unavailable.
7. When could the design reach commercial applications? No commercial timetable has been announced. The published performance figures are derived from simulations, and the next stages would normally include prototype construction, laboratory testing and evaluation under representative loads. Vehicle, vessel or aircraft integration would then require application-specific engineering, durability trials and regulatory or certification work. Heavy-duty trucks and off-highway demonstrators may offer a less restrictive validation route than commercial aviation, where certification demands are particularly extensive. Progress will also depend on manufacturer interest, intellectual-property arrangements, production feasibility and whether physical testing confirms meaningful lifecycle and packaging advantages.
8. What should manufacturers examine before adopting the architecture? Manufacturers should assess the complete propulsion system rather than the headline reduction figures alone. Important considerations include motor winding manufacturability, inverter controls, switching behaviour, efficiency, electromagnetic compatibility, fault tolerance, insulation life and thermal performance. They should also evaluate the architecture across real duty cycles and environmental conditions, including vibration, contamination and temperature extremes. Commercial analysis should consider whether reduced electrical stress lowers cooling requirements, component ratings, maintenance costs or warranty exposure. Any benefit must be balanced against redesign work, validation costs, supplier capability and the implications for servicing the dual-inverter system in the field.

Strategic Takeaways

1. Reducing electrical stress through inverter and motor architecture could help high-power electrification advance without a corresponding increase in filters, cooling hardware and component count.
2. ORNL’s simulation results are technically promising, but physical validation will determine whether the reductions produce measurable gains in efficiency, durability and lifecycle cost.
3. Construction equipment and heavy-duty vehicle manufacturers could benefit where sustained loads make capacitor heating, electromagnetic interference and motor-drive reliability major operational concerns.
4. Integrating the design into new platforms is likely to be more practical than retrofitting existing machines because the approach includes a change to the motor winding configuration.
5. Future procurement decisions will depend on demonstrated uptime and total cost of ownership, making machine-level trials more commercially decisive than performance figures obtained in isolation.