Mild Hybrid Vehicle Research Articles

Increasing the efficiency of the automotive generator due to active rectification

Problem. Increasing fuel economy requirements for modern vehicles lead to an increase in their electrification. The rise in the number of electrical systems leads to a higher load on the electrical power supply system, with the vehicle's power load reaching 2-3 kW. Leading automobile companies have begun serial production of vehicles with the new 12/48 V power supply voltage standard. The traditional alternator used today is a synchronous alternator, and rectifier diodes are used to convert the generated AC to DC to charge the battery, which is inefficient. A study of losses in an automobile alternator shows that the diode rectifier creates a significant portion of the machine's losses at low speeds, resulting in increased fuel consumption. The solution to this problem is to use a synchronous rectifier to replace traditional rectifier diodes, thus improving the efficiency of the AC/DC rectifier. Goal: To improve the economic and environmental characteristics of a mild hybrid vehicle through the use of a synchronous two-semi-periodic rectifier with a midpoint in the car generator. Methodology: Analytical methods are used to calculate energy losses on diodes and in the phase windings of the generator when employing a two-semiperiod rectifier with a midpoint, compared to a bridge rectifier. Results: The structure, functions, and operation modes of the synchronous rectification system are considered. The effect of synchronous rectification on the generator efficiency of a mild hybrid vehicle is analyzed. It was determined which configurations of synchronous rectification are more effective from the standpoint of energy saving and under which operating conditions. It was determined that in a two-semiperiod rectifier with a midpoint, compared to a bridge rectifier, there will be the same heating of the phase windings and 2 times fewer losses on the diodes. Practical value: A version of the bridge synchronous rectification system of the 48 V generator for a mild hybrid vehicle using MOSFET transistors and specialized control IC is proposed. A synchronous rectification system and its circuit implementation for a 12 V generator based on a two-semi-periodic rectifier scheme with a midpoint is proposed, which allows increasing the energy efficiency and economy of the automobile generator.

A ZVS Bidirectional 48V/12V Converter with Magnetic Integration for 48V Mild Hybrid Vehicles

A ZVS Bidirectional 48V/12V Converter with Magnetic Integration for 48V Mild Hybrid Vehicles

Drive cycle simulation of light duty mild hybrid vehicles powered by hydrogen engine

In the ongoing efforts to reduce CO2 and pollutant emissions, hydrogen combustion engine can provide immediately available mature technology for carbon-free transportation. Hydrogen combustion does not produce on-site CO2 emissions, the principal pollutant is NOx (which can be minimized using appropriate combustion control and aftertreatment), and the available ICE technology can be readily modified to accommodate for hydrogen use. The paper provides a prediction of the performance of a hydrogen combustion engine in passenger vehicles, aiming at extending or updating the available research with the current powertrain trends, namely downsizing, turbocharging, and hybridization. Data gathered from a single-cylinder engine fueled by a lean hydrogen mixture are used as input into a mild hybrid vehicle model, which is used for quasi-static drive cycle simulations. The results show NOx emission around the EURO VI limit without the use of any aftertreatment and fuel consumption as low as 1.1 kgH2/100 km in WLTC.

Battery sizing of 48 V plug-in hybrids considering calendar and cycle degradation

Plug-in hybrid electric vehicles (PHEVs) with battery packs tailored to the driving use case can help to reduce the environmental footprint of the transportation sector. Compared to common high-voltage systems, PHEVs based on a low-voltage level show a higher fuel consumption, but in return benefit from lower component costs and allow the utilization of cheaper high-energy cells. In this paper, the battery size of a 48 V PHEV concept is optimized to minimize the operational costs while taking battery degradation into account and ensure a lifetime-robust system layout. To investigate the applicability of high-energy batteries, 31 automotive-grade cells were investigated experimentally in a calendar and cycle aging study. The results show that calendar aging has a significant contribution of 17.5 % to the overall capacity loss and should be considered during the battery design process. The cycle degradation model is integrated in a Dynamic Programming simulation environment with various real-driving speed and slope profiles, which are extracted from a measured year-round driving profile. The simulation results show, that considering the degradation in the energy management strategy reduces the capacity loss but results in higher operational costs throughout the vehicle lifetime. The extension of a mild hybrid vehicle to a PHEV can reduce the operational costs by 18.5 %. If the vehicle is not charged, the costs increase by 6 % highlighting the need for frequent charging of PHEVs.

Asynchronous Motor in a Mild Hybrid Vehicle

Problem. Strengthening requirements for reducing CO2 emissions requires reducing fuel consumption in cars with internal combustion engines. One of the ways to solve this problem is to equip cars with a hybrid power plant that combines an internal combustion engine and an electric motor. A classic hybrid vehicle requires two energy sources: a fuel tank for the internal combustion engine and a power battery for the electric motor. Therefore, hybrid vehicle has a more complex design and a relatively high cost. A mild hybrid vehicle is a new concept of a hybrid vehicle for urban use that is emerging today. Such MHVs have a simpler design and also allow you to save up to 30% of fuel in urban driving mode. Goal. The purpose of the work is to improve the economic and environmental characteristics of a mild hybrid car, due to the use of an inexpensive asynchronous electric motor with frequency control in the scalar mode, as well as more effective use of power plant control system algorithms. Methodology. Analytical research methods were used to develop algorithms for effective use of the power plant in acceleration, uniform motion, regenerative braking, and stopping modes. Mathematical modeling and calculation methods were used to justify the use of an asynchronous motor for the power plant of a mild hybrid vehicle. Results. The use of a low-power asynchronous motor in the power plant of a mild hybrid vehicle is mathematically justified. The use of the principle of rational amplitude-frequency scalar control is proposed. An algorithm and a scheme for the implementation of an induction motor control system with support for the optimal power factor have been developed. Originality. Instead of using a valve synchronous electric motor with an expensive control system, it is proposed to use an asynchronous motor, which has advantages in the power plant of a mild hybrid vehicle. An asynchronous motor will allow the use of effective algorithms of uniform motion and regenerative braking modes. Practical value. The design of a soft hybrid vehicle with the use of a low-power asynchronous electric motor makes it efficient and cost-effective. The scalar control method of an asynchronous motor, with the slip control, makes it possible to obtain a system with high control quality and lower cost of implementation.

Energy Management Strategy of Mild Hybrid Electric Vehicle Considering Motor Power Compensation

An energy management control strategy based on the instantaneous optimization method of equivalent consumption minimization strategy (ECMS) under motor power compensation for mild hybrid vehicles is proposed in this study to improve fuel economy and ensure the dynamic performance of cars. A mild hybrid platform is built, and the future supplementary model of electric energy and the future consumption model of electric energy are established according to different power flow directions. It determines the equivalent fuel consumption rate of powertrain as the objective function by defining the equivalent factor and corresponding derivation, carries out optimization calculation, and obtains the energy distribution relationship between the engine and the motor. The motor power compensation strategy based on the control strategy is adopted to solve the effect of turbocharged engines’ transient response on vehicle dynamics and fuel economy. The actual results showed that vehicle power and fuel economy can be improved under the control strategy and compensation strategy design. Meanwhile, different motors allow the compensating coefficient to have different power-boosting and fuel economy effects.

Development of a 48V Integrated Starter Generator for Mild Hybrid Vehicles

Development of a 48V Integrated Starter Generator for Mild Hybrid Vehicles

Internal Combustion Engine Starting and Torque Boosting Control System Design with Vibration Active Damping Features for a P0 Mild Hybrid Vehicle Configuration

In order to meet the increasingly stricter emissions’ regulations, road vehicles require additional technologies aimed at the reduction of emissions from the internal combustion engine (ICE). A favorable solution from the standpoint of costs and simplicity of integration is a 48-V electrical architecture utilizing a low-voltage/high-power induction machine, which operates as the so-called engine belt starter generator (BSG) coupled via a timing belt with the ICE crankshaft within a P0 mild hybrid power train and used for starting up and boosting of the ICE power output, as well as for recuperating kinetic energy during vehicle deceleration. The aim of this work was to design a vibration damping system for the belt transmission within the so-called front end accessory drive (FEAD), which couples the BSG with the ICE crankshaft and to test the control system by means of simulations for realistic operating regimes of the P0 mild hybrid power train in order to show the functionality of the proposed approach in terms of mild hybrid vehicle performance improvement. Simulation results have pointed out effective attenuation of belt compliance-related vibrations using the proposed active damping control, with vibration magnitude reduced between three and five times compared to the default case during engine start-up phase. They have indicated the realistic belt slippage effects during engine start-up phase and have illustrated the effectiveness of the FEAD torque boosting capability with 30% gain in acceleration during vehicle launch.

Analysis of Real-Driving Data Variability for Connected Vehicle Diagnostics

Connected vehicle paradigm allows the systematic recording of data, which may be made available for both on-board and cloud diagnostics functions. However, real-driving conditions may be highly dynamic, making the application of diagnostic methods cumbersome. This article analyzes the variability of real-world data coming from a mild hybrid vehicle at various levels (i.e., vehicle, powertrain and engine cycle). The results show that although non-steady, real-driving conditions can exhibit situations that could be leveraged to characterize the nominal operation of the vehicle over time and therefore ease the detection of faulty operation.

Battery State-of-Charge-Driven Control of a Solar Mild-Hybrid Vehicle

Battery State-of-Charge-Driven Control of a Solar Mild-Hybrid Vehicle

A novel acceleration-based mode selection approach in mild hybrid vehicles

When the regulations were first formulated in 2008, one of the potential way’s automakers were supposed to meet the goal of 95g CO2/km by 2020/21 was the hybridization of vehicles. Market participants and customers are becoming more interested in electric vehicles. Infrastructure, high-power device complexity, driving distance and requirements for protection all seem to be obstacles that will take longer than anticipated to integrate, followed by fuel cell vehicles, which will be the new significant thing, particularly in the commercial vehicle segment. As an outcome, hybrid vehicles with 48V architecture are perceived as the forerunners of complete electrification. It outperforms traditional in terms of fuel efficiency and high voltage hybrids in terms of price and time-to-market. Evaluating a control approach for torque management between the motor and engine and mode change decision, namely, from electric to the hybrid mode or likewise, is a major challenge for automotive service providers for hybrid electric cars. Each of these dynamics will directly affect fuel efficiency and manoeuvrability, notably during mode transition. Research work presented and examines a new idea for improved driving dynamics on a P3 mild gasoline car in Modified Indian Driving Cycle (MIDC) 1ST stage (urban) under system constraints such as sustaining 12V battery voltage, lower battery 48V SOC, and so on. The novel method that has been implemented is focused on two techniques. I. A modified Adaptive Equivalent fuel consumption minimization strategy for the engine’s and the motor’s power distribution, and II) A rules-based mode change decision.

Comparative Study of Three Stator Cooling Jackets for Electric Machine of Mild Hybrid Vehicle

Three stator cooling jacket concepts, including a new cooling jacket concept with parallel straight spiral channels, are evaluated for electric machine of mild hybrid electric car. Steady-state cooling jacket thermal flow analysis and transient-state full motor simulations with circumferential, axial, and spiral jacket concepts are carried out to predict their heat transfer performance and temperature distribution. A prototype motor has been made with the new jacket concept. Infrared thermography is performed to detect the transient temperature distribution of the motor stator windings and laminations for validation of the thermal flow analysis.

Data Preparation and Training Methodology for Modeling Lithium-Ion Batteries Using a Long Short-Term Memory Neural Network for Mild-Hybrid Vehicle Applications

Voltage models of lithium-ion batteries (LIB) are used to estimate their future voltages, based on the assumption of a specific current profile, in order to ensure that the LIB remains in a safe operation mode. Data of measurable physical features—current, voltage and temperature—are processed using both over- and undersampling methods, in order to obtain evenly distributed and, therefore, appropriate data to train the model. The trained recurrent neural network (RNN) consists of two long short-term memory (LSTM) layers and one dense layer. Validation measurements over a wide power and temperature range are carried out on a test bench, resulting in a mean absolute error (MAE) of 0.43 V and a mean squared error (MSE) of 0.40 V2. The raw data and modeling process can be carried out without any prior knowledge of LIBs or the tested battery. Due to the challenges involved in modeling the state-of-charge (SOC), measurements are used directly to model the behavior without taking the SOC estimation as an input feature or calculating it in an intermediate step.

The use of the mild hybrid system in vehicles with regard to exhaust emissions and their environmental impact

Pollution of the environment is a global phenomenon. The lack of specific actions to reduce environmental pollution can lead to an increase in the average temperature of the Earth's air and to global consequences. One of the important sectors affecting environmental pollution is transport, including road transport. Currently, intensive legislative and construction works are underway to reduce the emission of harmful substances from road transport. Meeting the requirements imposed by the European Union makes it necessary not only to make structural changes to combustion units or exhaust aftertreatment systems, but also to use additional systems supporting the operation of the main engine. This group includes, among others, Mild Hybrid propulsion systems and classic hybrid systems. Their application is to affect not only the possibility of reducing the swept volume of a combustion unit, while maintaining its operational parameters, but also to reduce the emission of harmful substances of exhaust gases. The conducted research and its analysis indicate the legitimacy of using a newer vehicle equipped with a modern propulsion system, i.e. Mild Hybrid, in real conditions. In the case of toxic emissions of exhaust gases, a difference in emissions of individual components is noticeable, depending on the chosen driving mode. However, it is worth mentioning the difference in the emission of nitrogen oxides and the number of particulate matters. Their emission is reduced in relation to a vehicle using a classic powertrain. The use of a modern propulsion system also improves reliability. The tested Mild Hybrid vehicle does not use a conventional alternator and starter. This eliminates the elements that are prone to damage in prolonged operation. This is an unquestionable advantage when taking into account the operation of the vehicle.

Lithium-ion cell requirements in a real-world 48 V system and implications for an extensive aging analysis

Mild hybrid vehicles with a 48 V vehicle electrical system are regarded as a great contribution for achieving the fleet-wide CO2 targets of many car manufacturers. For minimizing the fuel consumption the utilization of the 48 V battery has to be optimized. Knowledge about realistic load profiles of the lithium-ion battery in a mild hybrid application is essential to improve the component design and to avoid serious durability issues. In this paper, we investigate battery data of over 60 test drives with mild hybrid development vehicles, covering an accumulated driving distance of more than 7,000 km. Here, the electrical and thermal load of the high-power lithium-ion battery is characterized and critical operating conditions with regard to cell aging are identified. Differences with respect to the cycling conditions of batteries in fully electrified vehicles are highlighted. Application-oriented aging matrices are defined, which allow an evaluation of the lifetime and a detailed parametrization of an aging model. Our research helps to optimize and minimize testing effort based on insights from real world data. Moreover, it enables a better evaluation of new cell candidates in early development stages and proofs the conformity of lifetime requirements of early cell sample phases within vehicle development cycles.

DBC-Packaged Inverter Power Module for Integrated Motor-Inverter Design Used in 48 V Mild Hybrid Starter-Generator (MHSG) System

This paper presents an improved package design of an inverter power module specialized for the 48 V starter- generator used in 48 V mild hybrid vehicles. The inverter module, called the mild hybrid starter and generator (MHSG), is integrated with its motor for size/volume reduction. However, the integrated motor-inverter presents supplementary challenges, such as limited cooling capabilities, in addition to the challenges resulting from the elevated voltage of 48 V of the mild hybrid systems. The proposed MHSG power module addresses these challenges. Parallel-connected metal-oxide-semiconductor field-effect transistor (MOSFET) dies were solder-bonded onto a direct bonded copper (DBC) substrate, and three DBC substrates (providing six legs) were assembled in a custom housing mounted on a forced air cooler. Shunt resistors and surface-mount device components were also soldered onto the DBC substrates. For improved stability and balance, ribbon bonding was used instead of wire bonding, the module components were repositioned, and DBC patterns were adjusted. The aforementioned approaches minimized the parasitic inductance, unbalanced/concentrated current density, and maximum temperature of the 48 V MHSG inverter module. The proposed module was validated through multiphysics finite-element method (FEM) simulations, manufactured prototypes, and experiments, all of which confirmed that the proposed module exhibits the electrical/thermal characteristics required for 48 V integrated MHSG systems.

Comparative Concept Study of Passive Hybrid Energy Storage Systems in 48 V Mild Hybrid Vehicles Varying Lithium-Ion Battery and Supercapacitor Technologies

A single energy storage technology will deliver either high power or high energy density. In high cycle applications like 48 V mild hybrid electric vehicles, lithium-ion batteries or supercapacitors have to be oversized to meet power, energy and cycle life requirements. However, a passive hybrid energy storage system is able to meet those challenges, but its performance depends on several factors. In this study, simulations and experimental investigations show how the design and operation conditions influence the performance of a passive hybridized system. In a comparative study for 48 V systems, consequences on performance are discussed.

Electric Motor and Dry Clutch Control in Launch Manoeuvres of Mild-Hybrid Vehicles Based on AMT/DCT Transmissions

Mild-Hybrid Electric Vehicles (mild-HEVs) earned market share over the last years an as effective roadmap to limit air pollution in big cities. In addition to this role, hybrid propulsion can be used to avoid dry clutch overheating in mild-HEVs equipped with automated manual transmissions. Indeed, high thermal level could result in serious damaging of dry clutch linings with very fast decay of expected lifespan affecting vehicle reliability. This paper shows results of vehicle launch simulations to highlight how the propulsion due to electric motor can effectively reduce clutch thermal stress during the slipping phase.

Multiphysics Simulation Analysis and Design of Integrated Inverter Power Module for Electric Compressor Used in 48-V Mild Hybrid Vehicles

This paper presents designs, multiphysics finite-element method (FEM) and circuit simulations, and experimental validations of a three-phase inverter power module for an electric compressor (e-Compressor) used in 48-V mild hybrid vehicles. The inverter module is integrated with its motor and scroll. The integration and e-Compressor operation situations raise sequential challenges in the module design and analysis. Thus, the e-Compressor module employs a direct bonded copper (DBC) substrate on which MOSFET dies, shunt resistors, and other electronics are soldered. Multiphysics FEM and circuit simulations are conducted to analyze (and minimize) the parasitic and loop inductances, current concentration, and temperature elevation of the design. The modeling and simulation processes are customized to represent the integrated DBC-based e-Compressor module, including the determination of loop inductance and overshoot voltage by considering systemic current conduction and reasonable simplification of cooling fluid effects. The simulation process and module performances are validated by experiments. The designed e-Compressor inverter module is improved to fully satisfy all the required specifications. Moreover, an excellent agreement between the simulation and the experimental results is confirmed, demonstrating the similar reductions of: 1) loop inductances simulated by FEM (~57%); 2) circuit-simulated overshoot voltages (~47%); and 3) experimentally measured overshoot voltages (~53%).

Visualization and quantitative evaluation of eddy current loss in bar-wound type permanent magnet synchronous motor for mild-hybrid vehicles

This paper describes the conductor eddy current loss that occurs in a permanent magnet type synchronous motor with a distributed winding stator using a rectangular copper wire designed for mild hybrid system applications for small vehicles. Compared with the conventional round wire inserter method, the space factor can be improved and the coil-end length can be shortened by applying a so-called hairpin windings using a pre-formed into hairpin shape of bar conductor, and as a result, DC current resistance of the armature winding can be reduced. However, since the conductor cross-sectional area tends to increases, the conductor eddy current loss generated by the space harmonics linkage becomes too large to ignore. In order to study the reduction of the conductor eddy current loss, it is important to visualize the spatial leakage flux distribution which causes loss and finely analyze how the magnetic path is formed. Therefore, analysis of the conductor eddy current loss distribution generated in the bar-wound conductor is performed using the CAE model that faithfully reproduces the coil-end shape of the actual machine. Furthermore, it was qualitatively clarified what ratio of conductor eddy current loss at various driving points. Finally, the results of preliminary study on reduction of conductor eddy current loss are reported.