See the Unseen from NVH Performance of E-powertrain – the Un-audible High Voltage Ripple and Transients that Affects EVs

Xiao Cai, Chairman & CTO, Stropower Technologies Co., Ltd.

• The correlation factors between the NVH performance of e-drive vehicles and its inner high-voltage power network
• Extensive impact of underlying electrical fluctuations and transients on electric drive vehicles
• Development of industry testing standards and testing environment

A key difference in NVH performance between e-drive vehicles and internal combustion engine (ICE) vehicles lies in the electromagnetic excitation vibration caused by the vehicle’s electric drive, such as the humming of the battery pack and the characteristic noise of the motor‘s electrical speed in the high dynamic region. This is the NVH characteristic of the high-voltage system of e-drive vehicles that can be perceived when exposed. However, through a deeper understanding of its mechanism, we will see more widespread high-voltage electronic and electrical fluctuations and transients, which more often and silently affect the control performance – functional status – driving experience – safety and durability of the electric drive. Effective high-voltage testing can help us better predict these potential hazards.

The correlation factors between the NVH performance of e-drive vehicles and its inner high-voltage powernet.

The mechanical structure design and power transmission design of the vehicle body form the self-foundation of the vehicle’s NVH performance. With the assistance of good chassis suspension, noiseabsorbing layers, and wind noise isolation, luxurious and quiet models can achieve better NVH performance in terms of mechanical quality. This is a very important design field in the automotive industry. These measures and means are effective and primary for mechanical vibrations below 100 Hertz. However, in electric vehicle models, there are typical noises in the kilohertz frequency band. These comparably highfrequency noises cannot be effectively suppressed by the absorbing materials and traditionally designed body structures, nor can they be masked by other low-frequency noises due to the difference in timbre. And it suddenly brings about new problems in NVH engineering for e-drive vehicles.

The difference in noise sources is the cause of different timbres. The main noise sources existing inside e-drive vehicles are the electrical fluctuations and transients of the high-voltage system caused by the operations of various power semiconductor switches.

A typical phenomenon can illustrate this issue: when charging your laptop with a charger in a quiet room, in most cases, you can clearly hear the humming sound of the charger. This is a common acoustic noise in daily life caused by electromagnetic fluctuations. The reason is that the power transmission control of switching power supplies relies on the switching actions of power devices. During the use of electric vehicles, similar causes of noise can also often be found: a faint humming sound that can be heard even when the vehicle is not in motion after just being powered on, and the special tonality variation in accordance with your pedal position.

During the power fluctuation of several hundred kilowatts (x kW) in an electric vehicle, the voltage and current of the internal highvoltage system will be subjected to electrical fluctuation impacts of varying speeds, ranging from 1V/MS to 1V/ns, for example. In terms of the composition of the high-voltage system, different electronic and electrical units inside are connected in parallel to the DC bus supported by lithium battery packs and DC link capacitors, and they will experience varying degrees of interference.

By conducting ripple injection tests on the lithium battery packs of e-drive vehicles ranging from 10Hz to 150kHz – that is, by simulating the ripple amplitude of the DC bus voltage and applying it to the power battery pack, the acoustic noise spectrum generated by the power battery pack was tested.

From the test results: due to the high-voltage battery pack characteristics of power batteries, there are several uH components in their internal impedance characteristics in the equivalent model at the circuit level. This enables ist response to fluctuations in AC voltage to generate an AC current with a sufficiently high phase difference – that is, the AC current intensity of the power battery pack varies with frequency according to its own impedance-frequency characteristics (D-EIS or in-situ EIS). This also leads to the NVH noise tones produced by the fluctuations of bus voltages of different frequencies on the battery pack being quite distinct. Based on the current test results, the corresponding relationship between the magnetic field stress of the current and the structural vibration (such as copper bars and metal covers) also confirms the causal relationship of frequency correspondence.

Effective control of electromagnetic interference fluctuations that may generate NVH excitation is currently an important research topic in high-voltage electronic and electrical testing. However, due to the very wide differences in the „excitation – transmission – response“ path among different vehicle models, the applicability of general models is limited. More prediction and verification methods still require appropriate test platforms for verification.

Take the electric drive power unit as an example. Under different power density design requirements, the controlled performance of the motor and the electrical shocks, such as ripple and surge, caused by the high-voltage system during the power output process, are related to the designer‘s optimization level of the control process, as well as appropriate peripheral filtering and anti-interference measures. The final production vehicle’s torque ripple wave and NVH characteristics are the result of design efforts coming from multiple aspects.

Extensive impact of underlying electrical fluctuations and transients on electric drive vehicles

The above description of the explicit NVH performance of vehicles has revealed the impact of electrical fluctuations and transients within the high-voltage system of e-drive vehicles on them, a problem that has not been encountered in ICE models.

In fact, since the large-scale commercial use of electric vehicles began, vehicle problems caused by the dynamic stress of high-voltage electrical systems have been very frequent, and most of these problems do not occur in a way that drivers can perceive.

For example: due to the excessive AC current at the impedance resonance point formed by the high-voltage wiring loop, the relay disengages and the BMS protection signal is mistakenly triggered; the overvoltage warning shutdown of the TMS is triggered by the voltage fluctuation of the DC bus caused by the operation of the MCU; the overvoltage of the DC bus which caused by the energy regnerated during heavy braking, which breaks down the components, etc. From the various electrical dynamics of high-voltage systems that have been mentioned, the major types of threat factors that mainly emerged can be classified in terms of waveform as:

1. Ripple during steady status
2. Transients during dynamic motion

Among them, the steady-state ripple mainly refers to the regular fluctuations in the bus voltage caused by the controller during the process of stabilizing the power output.

Under normal circumstances, since the on-off control of the switching elements by the controller is implemented by the software, if the load current fluctuates within a defined tolerance range, the command response for a stable Output is completed. This process is usually achieved at a steady state through „feedback-control“, such as typical PID control or complex PID control with algorithm update functions. The timing pulses of the switch nodes formed by the on-off control constitute the AC excitation of the entire in-vehicle high-voltage system, and through the impedance network of the system, the bus current is ultimately formed – this is a typical controlled response. Therefore, the level of ripple is directly related to the excitation composition, which is also the key way to usually increase performance or avoid the frequency of feature problems through control and regulation.

Transients during dynamic motion often occur in an „uncontrolled“ state, such as in a typical load-dump situation: the energy shock and high-voltage pulses generated by the drastic changes in current are natural responses without any controller management, and the survivability of the component unit solely depends on the stress margin at the time of design.

Another type of transient occurs with a higher probability. It also appears at the semiconductor nodes of the power bridge; that is, during the instantaneous process of the bridge arm switching, the voltage or current pulse is commonly seen at the rising and falling edges of the switching waveform. Although these transients cannot be regarded as truly „uncontrolled“, in fact, once a piece of hardware design is completed, it is very difficult to make changes to the ramping rates.

So, it is not difficult to see that the main difference between ripple and transient lies in the rate of voltage change, that is: V/s. Inside e-drive vehicles, with the development of the design trend towards functional integration, more and more functional units are gradually integrated into the same high-voltage system. For instance, several inverters are added to achieve an outdoor power supply, a step-up and step-down voltage module is added to be compatible with high and low voltage charging piles, and a 48V module is added for functionality and comfort, etc. Different units operate at different frequencies, which will apply more voltage variability on the DC bus. As a result, the generation of interference and the verification of anti-interference become important.

Development of industry testing standards and testing environment

At present, the industry is still in the research and early standard establishment stage for the design control and suppression countermeasures of ripple and transient pulses in EVs.

Conducting electronic and electrical tests on the high-voltage system of electric vehicles can simulate the extremely large electrical stress that occurs, thereby verifying the safety design margin and functional anti-interference capability of each component unit inside the vehicle. Avoid situations that threaten driving safety and affect the driver‘s experience.

Starting from the early LV123 standard, mainstream European car manufacturers have made many early efforts in the high-voltage electronic and electrical testing standards of vehicles, such as VW80300.

Today, the main general standards referred to in the industry are ISO 21498-1, -2. Since 2023, Vehicle manufacturers and testing institutions in China have gradually begun to pay attention to the corresponding testing standards and have already made preparations for the release of the corresponding Chinese standards as the testing progresses, and it is expected that the corresponding standards will be released within the next one or two years. In the future, based on the relevant test results and the accumulation of more new test cases, there will also be updated standards to gradually improve the current test standards, enabling them to provide more valuable references for detecting potential design issues of vehicles.

Stropower Technologies has always been dedicated to the development of green energy and the Research and development of zero-emission vehicles R&D. As a major equipment supplier for lithium battery testing and a leading enterprise in the electronic and electrical testing of high-voltage systems for electric vehicles.

Since 2018, based on the VW80300-2016 standard, the world’s first vehicle ripple spectrum response analyzer that fully meets the standard requirements has been developed by Stropower Technologies. Subsequently, it became the first supplier to offer a complete set of test equipment, including different voltage ramping rates and transient pulses.

Stropower Technologies officially released the third-generation vehicle high-voltage electronic and electrical complete test solution in October 2024, which includes a wide-frequency ripple disturbance emulator, a program-controlled test power supply system up to 1200V-1000A, a high-voltage artificial network that fully meets the impedance spectrum characteristics, and other auxiliary test equipment modules. It is a leading test solution provider in the industry that fully complies with test requirements and can comprehensively cover the main power dynamic ranges.

Thanks to the vigorous development of the electric vehicle market in China and the long-term trust and support of major vehicle manufacturers and testing institutions for Stropower Technologies, through the accumulation of hundreds of test cases, the company can not only provide customers with a one-stop complete set of test equipment assembly solutions, moreover, it can provide customers with professional and predictive test environment setup based on their testing purposes and the characteristics of the objects under test, avoiding time waste caused by the lack of understanding of tests and interferences from related variable factors. It also offers professional suggestions and technical support for the correct conduct of tests and the accuracy of test results.

Posted on 4th February 2026

DI (FH) Wilhelm Vallant, Product and Business Development Manager Transmission & E-axle, AVL List GmbH

The automotive sector is experiencing a profound transformation towards electrification, motivated by the dual objectives of mitigating greenhouse gas emissions and ensuring uncompromised vehicle performance. Original Equipment Manufacturers (OEMs) are increasingly challenged to meet rigorous sustainability and cost-efficiency benchmarks. In response, AVL introduces a forward thinking and validated solution that establishes new standards in electric drive unit (EDU) efficiency, lifecycle CO2 emissions reduction, and system integration.

This article details the development and empirical validation of a high-efficiency EDU system that achieves an average cycle efficiency exceeding 94 % under the Worldwide Harmonized Light Vehicles Test Procedure (WLTP) as well as the China Light-Duty Vehicle Test Cycle (CLTC) and maintains vehicle energy consumption below 10 kWh per 100 km. The discussion further encompasses the technological advancements and sustainability frameworks that underpin these accomplishments.

EDU Architecture and Operational Strategy

At the core of a demonstrator vehicle developed by AVL as part of an R&D project lies a dual-motor EDU configuration consisting of:

• Two Permanent Magnet Synchronous Machines (PMSMs)
• A compact, single-stage spur-gear transmission with double helical gears
• Compact final drive with integrated planetary gear differential
• A dual Silicon Carbide (SiC) inverter system
• Oil catch tank to decrease the oil level during operation

o meet the ambitious energy consumption and efficiency goals, an innovation-driven development process was implemented, enabling the early-stage comparison of a wide range of technologies. By applying advanced simulation methods, numerous potential solutions can be evaluated early on in terms of their alignment with the project objectives. Key measures include component technology selection, architectural studies to balance performance and losses and system simulation using AVL’s proprietary development toolchain, the Powertrain System Optimizer (PSO). Step by step, the number of possible variants is reduced by selecting the most promising solutions, while the level of simulation detail is progressively increased. Once only a few options remain, detailed component optimization and initial control strategy refinement are carried out in the final development phase. FIGURE 1 illustrates the AVL PSO methodology.

Figure 1: AVL Powertrain System Optimizer Workflow

The selection of transmission, electric motor and inverter technologies was guided by cost reduction and sustainability, with a focus on intelligent integration, minimizing drag losses and using efficient materials. Achieving maximum efficiency in the EDU architecture was essential to reaching a WLTP cycle efficiency of more than 94 %, and a dual-motor concept proved to be the most effective solution. The main motor was designed for efficient continuous operation, while the secondary motor supports boosting and recuperation. This secondary motor, which can be decoupled via a dog clutch, was specifically optimized for its intended use and the load points defined by the operating strategy.

Figure 2: Sustainability in the Drivetrain – Impact of Development Phase on Lifecycle GHG Emissions

The AVL PSO development methodology was used to optimize the EDU’s dimensions, simulating numerous variants to evaluate efficiency and performance under varying parameters. The basic design specification was derived from system simulations, with components and operating strategies already optimized during the early concept phase.

Outcome of this design evolution process is a unique system featuring key elements to support the lowest possible energy consumption in the vehicle. The gear-set features a single stage transmission with double helix gears, reducing mechanical losses in high torque and speed operating conditions by -16 % compared to conventional designs. In moderate torque and speed losses are reduced by 11 %. To enable compact packaging of the two e-Motors a planetary differential is used which could be packaged inside the double helix final drive gear with an axial length of less than 80 mm. The lightweight design reduces weight by -15 % to -20 % compared to conventional solutions.

An oil catch tank is positioned at the differential gear to collect oil effectively. This collected oil is then distributed to various components, including gears, bearings, and the dog clutch. Besides securing proper lubrication of the system the oil catch tank also lowers the oil level in the transmission sump, thus reducing splash-losses while the vehicle is running. The key element for enabling the operation of the boost electric motor is an electromechanically actuated disconnect clutch located on the e-Motor shaft. When it is not engaged, it is ensuring
operational efficiency.

To ensure safe operation of the dog clutch a special simulation experiment was set up to analyze the impact of the stator windings magnetic field on the dog clutch’s actuation force. Based on this investigation, using the advanced in-house simulation capabilities, it was possible in a virtual stage to evaluate a safe operation of the dog clutch under all operating conditions.

With introduction of the disconnect clutch enabled the implementation of an operating strategy, further contributing to highest possible system efficiency hence contributing to lowest possible energy consumption.

Design-to-CO2 Methodology

Considering the complete life cycle as a system with certain limits is essential for a valid analysis. Automotive manufacturers can influence most scope 1 and 2 emissions according to the Greenhouse Gas (GHG) Protocol Corporate Standard (2) and have certain but not full control of the upstream scope 3 emissions of the supply chain, as well as the scope 3 emissions downstream in the usage and recycling phases (3).

In product life cycle modelling, it is important to know the qualitative patterns for CO 2 e influenceability, determination and the actual occurrence to define appropriate optimization measures at the right times.

FIGURE 2 shows an ideal-typical pattern for the product life cycle of a Battery Electric Vehicle (BEV) assuming a European 2023 electricity mix in the production and in-use phase (1). It is shown that the CO 2 e influenceability decreases significantly during the later phases described. Although the majority of CO 2 e emissions occur during the production phase and typically need to be offset during the in-use phase when compared to other powertrain technologies, the development phase has the most significant impact on the CO 2 e footprint.

By integrating life cycle assessment (LCA) methodologies and sustainability criteria from the outset, developers can evaluate and compare the environmental impacts of various powertrain technologies. This proactive approach enables the identification of technologies that not only meet performance and cost requirements but also minimize CO 2 e emissions throughout the product’s life cycle. Consequently, making informed decisions early in the development process ensures that the chosen technology aligns with sustainability goals, leading to a more environmentally friendly product.

Through the integration of these cutting-edge technologies, AVL enables OEMs to deliver electric powertrains that excel in performance, efficiency, and sustainability. This advancement constitutes a significant milestone toward fulfilling the automotive industry’s climate objectives while preserving competitive product offerings.

Real Life Demonstrator

From the outset, the goal was to transfer the resulting technology into customer applications, aiming for comparable efficiency and consumption values in the target vehicle. When the EDU was integrated into a customer vehicle based on the original design, a slight efficiency loss was initially observed due to different driving conditions and load points. However, the efficiency still significantly improved the customer’s baseline EDU. To meet the original efficiency targets, goal-oriented adjustments were necessary. Subsequently, the electric motor topologies and gear ratios were optimized. The adaptation process included detailed investigations to improve efficiency under the boundary of materials usage comparable to benchmark solutions. All modifications were made with the updated customer load profile and the geometric constraints of the target vehicle in mind, ensuring seamless integration. Vehicle simulations confirmed the effectiveness of these measures, achieving an average customer cycle efficiency of more than 94 %.

The EDU was tested both on a test bench and in the vehicle to validate system efficiency. While the test bench results did not exceed the 94 % cycle efficiency target, further optimization of the operating strategy for in-vehicle use led to an average efficiency of 94.4 % during real-world testing, confirming the achievement of the project goals.

Conclusion

AVL has developed a high-efficiency electric drive unit (EDU) achieving over 94 % cycle efficiency under WLTP and CLTC standards, with vehicle energy consumption below 10 kWh/100 km. The EDU features a dual-motor configuration with permanent magnet synchronous machines, a single-stage double helical gears transmission, and a dual SiC inverter system, optimized through AVL’s Powertrain System Optimizer. Innovations include a lightweight, compact design with reduced mechanical losses and an electromechanically actuated disconnect clutch to enhance efficiency. The development incorporated lifecycle CO₂ assessments to align with sustainability goals, emphasizing early-stage optimization to minimize emissions. Real-world vehicle integration confirmed the system‘s efficiency, reaching 94.4 % in testing, demonstrating a significant advancement in electric powertrain performance and environmental impact reduction enabled thorough AVL technology and engineering methodology.

Validated Outcomes:

• Achieved an average EDU efficiency of more than 94 % in real-world testing scenarios
• Recorded 94.4 % efficiency in customer-specific driving cycles

Quotes:

• „>94 % EDU efficiency and <10 kWh/100 km energy demand – validated on the road, not just in simulation.“
• „Design-to-CO2e turns sustainability into an engineering parameter, not a marketing claim.“

Our future hybrids are designed to fit in all current BEV platforms

In addition to dedicated hybrid transmissions, Horse Powertrain also supplies dedicated combustion engines and complete drive modules. At the 28th CTI Symposium in Berlin last December, we spoke to Ingo Scholten, CTO of Horse Powertrain, about developments in current and future hybrid technology.

Mr. Scholten, Horse Powertrain has a broad portfolio of hybrid drives, but also produces its own dedicated hybrid engines and ICEs. That’s unusual for a Tier 1 supplier …

It is. There used to be a lot of ‘transmission-only’ suppliers for manual transmissions, automatics etcetera. But usually, OEMs made their engines and dedicated hybrid transmissions, or DHTs, in-house. Now we offer both – as a system supplier. That makes us quite special to our partners. Instead of just components, we can also offer entire drive systems – plus full integration support, including topics like emissions and homologation.

What are customers asking for?

Firstly and naturally, we still make drives for Geely and Renault, our parent companies. The Renault E-Tech hybrid, for instance, is now in its third generation. For Mercedes, we supply a 1.5-liter combustion engine for mild hybrids. In China, we’re developing our dual-motor DHTs, which now use dual-shaft transmissions instead of planetary gearing in earlier years. And we’re talking to other customers in Europe and the US. The demand there for full hybrids is even stronger than in China, but they also want PHEVs. We are discussing range extenders more and more, too. In China, it’s mostly long-range PHEVs with a parallel option; they have big traction motors, and drive like EVs. In Europe, drivers still use manual transmissions so multi speed system are accepted even in combination with electrification. But in China, multi-speed transmissions can be a problem because customers there expect an EV driving experience.

Dual-motor hybrid drives are gaining ground. When do you use serial-only, and when is serial-parallel better?

For maximum efficiency, including on highways and rural roads, you’d normally use serial-parallel – mostly P1 and P3. A serial-only drive would cost you 4-5% in efficiency. Parallel or multi-speed transmissions are better for higher tractive force requirements. P2 still has its place for small vehicles in segments A or B. And if you already have an all-wheel-drive system with an electric rear axle, P2 is fine there too; you don’t really need a hybrid drive with two electric motors in the front then. P2 can also work when OEMs design vehicles as ‘BEV native’ or ‘BEV first’, respectively. Space is limited, so a P2 with a single electric motor can be practical when a market needs a hybrid variant of the BEV.

Looking at P1/P3 hybrids, we’re seeing solutions with a single fixed gear, and solutions with two, three, or four gears. What do you think will prevail?

When markets want cars that ‘drive like a BEV’, it makes sense to have fewer gears. Often, just one is enough. For high towing capacity, you can use multiple gears to modulate tractive force. When customers ask us for advice, we often recommend either a large traction motor with one fixed gear or a powertrain with four gears and a smaller traction motor. As I mentioned, Renault has a successful solution that’s now in its third generation.

Many OEMs still need two vehicle platforms; others are moving to ‘BEV first’ and using a BEV platform for hybrids, too. What’s your approach?

That’s currently one of our main topics, as I showed in my presentation here at CTI. Some vehicles still use traditional hybrid architectures, which require certain compromises; others use BEV-only architectures. A hybrid drive with one or two electric motors requires more space than an ICE-only drive, whereas a BEV drive requires much less. So, if you optimize a vehicle’s front end for BEV, the installation space is shorter and, above all, narrower. The subframe mountings are configured differently, the drive shafts sometimes go in front of the axle. And then a traditional hybrid drive won’t fit. You need a hybrid drive design that fits within a BEV vehicle architecture without requiring OEMs to compromise their BEV optimization.

Which of your products meet that requirement?

Firstly, there’s our highly compact HORSE G10 for range extenders. It has a two-cylinder boxer engine with a compact pushrod design and a generator mounted directly on the crankshaft. Then we developed the HORSE C15, a range extender as well. This can be installed either vertically or horizontally. And then we have the Future Hybrid System, which is available in P2 or P1/P3. According to our research, it fits most of the dedicated BEV platforms currently available. So, if European customers with a BEV-first approach want a hybrid derivative for their platform, they can use these powertrains while still meeting all the BEV crash-test requirements.

You also offer dedicated hybrid combustion engines. What are their thermal efficiencies, and how much more is possible?

We are in production with over 44 percent break thermal efficiency. And those are figures from engineering, not marketing. We’re aiming for 49-50 percent. But to get there, we need to implement a few more technologies – for instance, lean combustion. We also then need to design exhaust systems that won’t significantly increase overall system costs. On the other hand, ICE dynamics are lower in serial operation, so that simplifies exhaust after-treatment to a certain extent. For tomorrow’s lean-burn engines, the key is to keep lambda above 2.2 as much as possible so after-treatment doesn’t get too complex.

Ingo Scholten during his presentation at the CTI Symposium 2025 in Berlin

How do you rate the potential of synthetic fuels in terms of lower CO2 emissions?

Nobody expects all the markets to switch to synthetic fuels in the short term. But it could well be a gradual process. In five years’ time, maybe we could add five percent of synthetic fuels, then later fifteen percent, or twenty. The really good thing is that you can reduce CO₂ across your whole existing fleet. Methanol is another field in which Geely is working. They started selling methanol engines in 2013. Originally, these were 100 percent methanol, designed for taxi fleets in regions where methanol was basically a by-product of coal mining. But now they’re working with bio-methanol and trying to create a circular economy there. At last year’s Vienna Motor Symposium, Geely presented onboard CO₂ capture for trucks, for example. Some innovations are just getting started, but we’re already seeing potential here and there.

The EU Commission has just reopened the window slightly for combustion engines after 2035. What do political decisions like this mean for Horse Powertrain?

None of our products is specifically designed for Europe. Our product strategy is very broad, with products we use in the European market, Brazil, India, and elsewhere. So, in terms of capacities and defining technical requirements, decisions about the time after 2035 don’t affect us that much. As a globally operating company, we offer solutions that can meet the requirements of various and changing markets.

Interview: Gernot Goppelt.