World Electr. Veh. J., Volume 7, Issue 2 (June 2015) – 20 articles , Pages 173-341

Under hilly road conditions, it is difficult to achieve near-optimal performance of energy management strategy (EMS) of fuel cell hybrid electric vehicle (FCHEV). In order to achieve near-optimality, optimal state reference trajectory is predicted based on future information, and thus reference tracking controller is often considered as real-time predictive EMS. There are two approaches depending on in what way the predicted reference will be used as follows: 1) position-based predictive EMS for tracking position- dependent reference, 2) time-based predictive EMS for tracking time-dependent reference. In this paper, analytical sensitivity analysis based on Pontryagin’s minimum principle (PMP) is performed to prove robustness of position-based predictive EMS with respect to velocity uncertainty. First, optimal control problem is formulated in time and position domain, and PMP approach is used to derive boundary value problem (BVP) that achieves global optimality. Then, sensitivity differential equations are developed which describe sensitivity of original BVP with respect to velocity uncertainty. Finally, these equations will be solved simultaneously with the original BVP to compute first-order sensitivity of time- and position- dependent optimal state. Results show that sensitivity of time-dependent optimal state is much bigger than that of position-dependent optimal state because velocity uncertainty can change predicted travel time, and this effect on sensitivity is significant. Therefore, predictive EMS should use current position to track position-dependent optimal state reference in terms of the robustness with respect to velocity uncertainty. Full article

This paper presents a reliability study of a directly cooled and an indirectly cooled IGBT module after a test drive of 85.000 Km in a fuel cell electric vehicle. In this case, the car was mainly driven on highway, only a minor part of the distance was driven in urban areas. At the end of the test drive, the power control unit was disassembled and analyzed with regard to the lifetime consumption. First, electrical measurements were carried out and the results were compared with the ones obtained directly after module production (End of Line test). After that, ultrasonic microscopy was performed in order to investigate any delamination in the solder layers. As a third step, an optical inspection was performed to monitor damages in the housing, formation of cracks or degradation of wire bonds. The results show none of the depicted failure modes could be found on the tested power modules after the field test. Obviously, no significant life time consumption could be observed. Full article

In this paper, a novel highly integrated System on Chip (SoC) based control unit concept is presented, which is conceived to combine the functionality of various powertrain ECUs and to additionally enhance their control with predictions based on the real-time execution of complex mathematical models. Such a platform has the potential for providing considerable benefits to upcoming hybrid and electric vehicles, especially for highly complex and efficient hybrid and multi-motor electric vehicles. A clear advantage is the reduction of Control Units, consequently also reducing the system complexity, communication requirements and development effort, which are directly associated to production and development costs. A controller architecture capable of exploiting the strength intrinsic to the nature of each platform type is presented, basing on the new generation of high-performance hybrid SoC platforms which combine powerful processors with cutting edge FPGAs. The parallel hardware paradigm of FPGAs enables the implementation into a single component not only of several Field Oriented Control loops for electrical motors, power management functions and vehicle-level optimizations, but also of advanced real-time predictive algorithms. The combination of so many complex tasks would not be feasible on a typical automotive microcontroller unit. A further objective for obtaining a highly integrated solution is to establish an efficient development and prototyping process, aiming to simplify and harmonize the workflow through the whole V model, by completely basing it on model-based-design tools. Finally, the concept demonstrator being implemented in this paper will combine a state-of-the-art high performance microprocessor and FPGA using a commercial SoC platform together with model-based software development tools. This will also fulfil the expectation of providing a topology with great migration and industrialization potential for the case of higher qualification requirements. Furthermore, it is another step towards a necessary mindset shift on control system development and integration methods for increasingly complex vehicles. Full article

Splitting power is a tricky problem for series plug-in hybrid electric vehicles (SPHEVs) for the multi-working modes of powertrain and the hard prediction of future power request of the vehicle. In this work, we present a methodology for splitting power for a battery pack and an auxiliary power unit (APU) in SPHEVs. The key steps in this methodology are (a) developing a hybrid automaton (HA) model to capture the power flows among the battery pack, the APU and a drive motor (b) forecasting a power request sequence through a Markov prediction model and the maximum likeli-hood estimation approach (c) formulating a constraint stochastic optimal control problem to minimize fuel consumption and at the same time guarantee the dynamic performance of the vehicle (d) solving the optimal control problem using the model predictive control technique and the YALMIP toolbox. Our simulation experimental results show that with our stochastic model predictive control strategy a series plug-in hybrid electric vehicle can save 1.544 L gasoline per 100 kilometers compared to another existing power splitting strategy. Full article

In a hybrid electric vehicle (HEV), the braking system is composed of friction braking and regenerative braking. When a driver presses the brake pedal, each braking system collaborates and applies braking torque. The friction brake is a hydraulic system which has a slow response time and the regenerative brake is an electric system which responds quickly. Such characteristics bring a control problem, especially transient characteristic of shifts between regenerative brake and friction brake, because the hydraulic system cannot follow the response time of the electric system. The friction braking torque is also governed by the friction coefficient which changes with temperature. This causes the braking torque to be generated differently with the demanded braking torque, without considering the temperature. Due to these problems, the driver would feel uncomfortable and the vehicle would be unstable resulting from the difference in response time and variance of the friction coefficient when pressing the brake pedal. Hence, it is essential to coincide the settling time of friction and regenerative braking system regarding the temperature. To solve these problems, the hydraulic system was mathematically modelled using the flow and continuity equations and the electric system was modelled using the d-q transformation and voltage equation. The temperature estimation model of the brake components was developed using the heat transfer methods which are conduction, convection and semi-infinite solid. The brake temperature was calculated by the finite difference method (FDM). With the mathematical model of hydraulic and electric systems, the coincidence control for the settling time of both systems was established. It was also possible to find the friction coefficient and calculate the braking torque by using the temperature estimator. In this paper, the numerical simulation was carried out to verify these control algorithms. The difference in response time between friction and regenerative braking system was reduced and the transient characteristic was improved. Also, the braking torque was compensated with the temperature, and the difference between demanded and actual braking torque lessen using the algorithms. Full article

This study describes method of regenerative breaking control for HEV with multispeed transmission. When a gear is shifted during regenerative breaking, almost all TMED HEVs in the world lose decelerate linearity or reduce regenerative breaking to get decelerate linearity. So fuel efficiency is get down. We made concept that is called regenerative breaking practical quantity. Regenerative breaking practical quantity solved problem of decelerate linearity. And this technology is used in all TMED HEVs of Hyundai motor group. Regenerative breaking practical quantity reflect a characteristic curves of motor, shifting process of multispeed transmission and following of hydraulic brake for cooperative control of HCU, MCU, TCU, AHB and so on. As a result of this technology, decelerate linearity is retained for sale the HEV. Furthermore fuel efficiency is improved about 8.4% because regenerative breaking quantity is increased about 28%. Full article

In this paper, control analysis was performed for a hybrid electric vehicle (HEV) equipped with a continuously variable transmission (CVT) under various driving conditions. First, a dynamic CVT model was developed by considering hydraulic and mechanical losses. The hydraulic loss accounts for the majority of the total losses at low vehicle speeds, whereas the mechanical loss accounts for the majority at high speeds. In addition, CVT ratio control and clamping force control strategies were developed, including manipulation of the CVT shift dynamics. On the basis of the dynamic model of the CVT, an HEV performance simulator was developed using Argonne National Laboratory (ANL)’s model-based simulation program, Autonomie. Second, by analysing the test results from ANL, an engine optimal operating line was constructed on the basis of the engine brake-specific fuel consumption. Third, the battery state-of-charge range and the battery characteristics of the maximum charging and discharging power were investigated. Using the analysis results, vehicle operation control strategies were developed for the acceleration, cruising, deceleration and idling modes. Also, control algorithms were developed for each vehicle operation mode. Finally, the control algorithms were verified by comparing the simulation results with the test results. Full article

This paper shows how a multiobjective problem is formulated and solved in order to size the components of a vehicle with a split hybrid transmission, such as a Toyota Prius. The goal is to explore feasible design options and the trade-offs between fuel economy and vehicle cost. Eight input variables are provided for this optimization, including plant variables such as maximum power ratings for engine, motors, and battery; final drive ratio; and control variables that determine how the battery energy is utilized. Three constraints are used: achievement of the battery charge balance, ability to trace the drive cycle, and ability to achieve a zero to 60 mph acceleration performance within 10 seconds. We describe a multiobjective optimization algorithm that we have implemented in Autonomie, a simulation tool developed at Argonne, and we demonstrate its ability to utilize parallel computing capabilities of Matlab. A parallel/distributed-computing infrastructure is used to simultaneously evaluate multiple combinations of input parameters, over multiple drive cycles, thereby reducing the overall time taken to perform the optimization and hence reduce the total solution time. The optimization produces several design choices, which form a Pareto front. The search algorithm ensures that as the number of iterations increases, more and more points are added on or near the Pareto front. All the points that form the front are relevant design choices, and the front characterizes the balance between conflicting goals such as fuel economy and performance. Full article

Since road traffic currently contributes 23% to CO₂ emission, the European Union forces car makers to reduce the average CO₂ emission of their fleet to 95g CO₂/km by 2021. This can only be achieved by electrification of vehicles. It is obvious that the market requires electrified vehicles to be comparable to combustion engine cars in price, driving range, maintenance effort, lifetime and safety. The main inverter, also called HPCU (hybrid control unit), with the power module as its core component plays a key role because it is a major lever for CO₂ reduction. The strict rules of the EC requires future power modules with highest power density, high voltage and high current rating, high temperature capability and cooling, sufficient lifetime, low weight and small size. The article describes how Infineon will meet the requirements of power modules for the coming years. On the power semiconductor technology side, a new IGBT generation will be introduced as well as a very thin IGBT technology. On the packaging side, two new packages will be introduced: a very compact low-cost generator module, and a high power motor module with significant improvements in power density and size, cost, stray inductance and efficiency. It will also be discussed how to further increase the robustness of such packages to allow operation at even higher operating temperatures. An insight into wide bandgap power semiconductor switches will also be given. The new technologies will reduce V_ce and switching losses at the same time and thereby increase inverter efficiency and power density. Full article

An electric vehicle conversion project often faces the problem of a sudden and non-smooth acceleration. From this, we see a great demand in improving the throttle control to have a better human-machine interface and better controllability and safe operation of an electric vehicle. Additional improvement on throttle control also helps to reduce energy consumption during acceleration which prolongs the driving range of the vehicle. This work presents a practical method to provide a smooth start for an electric vehicle with brushless DC (BLDC) motor using arduino microcontroller. Additional control algorithms between the throttle and motor controller are implemented with the microcontroller. Two sets of algorithm, which can be used at the same time, have been developed in order to reach the goal of smoother acceleration, better controllability, and lower energy consumption. Tests have been carried out on our in-house developed vehicle, Electric Caterham, to validate the effectiveness of different algorithms. We expect a 10% reduction in energy consumption during acceleration. This paper presents the change in acceleration performance after implementing the proposed feedback control system. Full article

The integrated longitudinal and lateral dynamic motion control is important for four wheel independent drive (4WID) electric vehicles. Under critical driving conditions, direct yaw moment control (DYC) has been proved as effective for vehicle handling stability and maneuverability by implementing optimized torque distribution of each wheel, especially with independent wheel drive electric vehicles. The intended vehicle path upon driver steering input is heavily depending on the instantaneous vehicle speed, body side slip and yaw rate of a vehicle, which can directly affect the steering effort of driver. In this paper, we propose a dynamic curvature controller (DCC) by applying a newly-defined parameter, the dynamic curvature of the path, derived from vehicle dynamic state variables; yaw rate, side slip angle, and speed of a vehicle. The proposed controller, combined with DYC and wheel longitudinal slip control, is to utilize the dynamic curvature as a target control parameter for a feedback, avoiding estimating the vehicle side-slip angle. The effectiveness of the proposed controller, in view of stability and improved handling, has been validated with numerical simulations and a series of experiments during cornering engaging a disturbance torque driven by two rear independent in-wheel motors of a 4WD micro electric vehicle. Full article

Since 2011 the Eindhoven University of Technology (TU/e) is using an in-house developed battery electric vehicle based on a Volkswagen Lupo 3L for educational and research projects. The TU/e Lupo Electric Lightweight (EL) is able to recuperate kinetic energy by using regenerative braking. A brake pedal based regenerative braking strategy demands applying a combination of hydraulic and regenerative brake force. A proper control of this brake blending proves to be challenging. An advantage of an electric vehicle compared to an ICE car is that substantial amounts of deceleration can be achieved without applying the friction brakes. These observations have led to the concept of One Pedal Driving (OPD) where the accelerator pedal can also be used to perform regenerative braking. A similar concept is applied in for example the BMW i3 and Tesla Model S and is rated quite positively by drivers. Since kinetic energy cannot be recuperated with 100% efficiency, for some driving conditions the best thing to do is neither propel nor brake the vehicle and just let the car roll freely, which is known as coasting. During coasting minimal energy is used which improves the overall energy efficiency. To assess regenerative braking strategies that are currently applied in electric vehicles, a selection of vehicles has been investigated. These vehicles are subjectively evaluated by driving tests on public roads where special attention is paid to the regenerative braking and coasting characteristics. Before designing a suitable OPD algorithm, a list of requirements is composed. The overall motor performance limits are investigated and based on the OPD requirements a general accelerator pedal map is designed and implemented. Based on a limited number of driving tests, subjective and objective conclusions regarding energy efficiency and drivability are drawn. The tests with various drivers indicate a slightly improved driving efficiency. Furthermore, all drivers comments positively on using OPD as being very intuitively and are able to adapt to it quickly. Full article

This paper proposes a control method robust against the rotor temperature variation for the induction machine used in the xEV traction application. The rotor resistance (or time constant) of the induction machine varies with the rotor temperature so that its torque control performance will be degraded if this variation is not properly compensated. In this paper, firstly a direct vector control method, which is based on the rotor flux estimator using the current model in the synchronous reference frame, is adopted in order to control the DQ-axis rotor fluxes independently. Secondly, the rotor time constant variation is compensated utilizing the flux estimation difference between the voltage and current models. This method has no transition region which is inevitable in the conventional method that uses the current model in the low speed region and the voltage model in the high speed range for estimating the rotor flux. The robustness to the temperature change of the proposed method is validated through the experiment in the motoring and regeneration modes. Full article

The novel Stator Cage Drive marks a paradigm shift in electrical machine design by substituting layers of windings with stator bars that are short-circuited on one end of the machine. Those bars are individually fed from the opposite end of the machine, utilizing dedicated power electronic switches. Instead of being limited to one fixed MMF-distribution in the air gap, it is now possible to incorporate new degrees of freedom into the control strategy for such a machine, e.g. pole-switching during operation with an asynchronous rotor and the creation of selected harmonics. Compared to conventional designs of traction drives for HEVs or BEVs, this drive architecture achieves a better efficiency, both in peak operation and using common drive cycles, it is cheaper in manufacturing and it also provides better fail-safety. In order to obtain a high-quality MMF-distribution, a number of individually fed stator bars as high as 60 is preferable, which also implies a higher complexity of the control of this machine than for three-phase counterparts. If for example an induction type rotor is chosen, it is possible to vary the number of poles during operation, thus allowing the machine to always operate in the region of highest efficiency, which usually lies in the field weakening region for induction machines. An overview of the capabilities of the ISCAD-Drive is given, the applicability of well-known control methods is investigated and matters of functional safety in current measurement for a high number of phases are discussed. Full article

Inverters for electric vehicle motor drive systems are essential in converting the battery's direct current into alternating current. Si(Silicon) IGBT that is commonly used in inverter modules have large Vce,sat and turn-off time due to p+ drain and tail current. Therefore, inverter modules consist of Si IGBT with relatively low efficiency. If we can use MOSFETs instead of IGBT in inverter modules, it is possible to achieve high efficiency because of short turn-off time and high operating frequency. Yet also has a problem; Si MOSFETs has large on-resistance compared to Si IGBTs. In this study, SiC(Silicon Carbide) was used to make MOSFETs instead of Si. Futhermore, an accumulation channel concept is adapted to a SiC trench MOSFET, namely Trench ACCUFET. Compared with conventional SiC trench MOSFETs, the novel SiC trench ACCUFET structure has not only lower on-resistance but also high breakdown voltage as shown by the simulation results. We fabricated the Trench ACCUFET for verification, and described improvements that is to be made. Full article

This paper presents a new optimization method to design a rotor structure for a permanent magnet motor that can reduce vibration. The optimization problem is formulated with a multi-objective function to minimize the fluctuation of the radial magnetic force and the torque ripple. To obtain the optimal rotor shape consisting of a permanent magnet and ferromagnetic material, a multiple level set model is employed to express the structural boundaries and magnetic properties of each material. The updating process of the level set function based on the adjoint sensitivity and the time evolutional equation makes it possible to obtain a novel rotor configuration of the motor. To verify the usefulness of the proposed method, a rotor design example of the surface-mounted permanent magnet motor for electric power steering system is performed. Full article

Abnormal electromagnetic noise of traction motor in hybrid electric vehicle (HEV) occurred after the endurance test is experimentally investigated. Theoretical model explains that the abnormal components, which are ±1 orders of the number of slots, can be sourced from an unbalanced rotor. Experimental approach confirms that the abnormal noise is mainly from the rotor. Since there are no variations in the strength of the magnet flux, the vibration of the magnets is strongly believed as the main reason of the abnormal noise. Finally, the magnetic fixing method is changed from bond to mold, and the improvement of the noise is demonstrated. Full article

Axial flux (AF) motors and generators have been used in niche automotive applications for many years. Given their disk like shape they offer distinct advantages for integration into hybrid powertrains where available length is limited. An overview of axial machine topologies is given and the design and performance laws that govern the sizing of axial flux permanent magnet machines are presented. Based on the analytical laws described it is shown that an axial machine can achieve significantly more torque than a size comparable radial machine. 3D finite element analysis is used to fine-tune designs and to investigate loss mechanisms. A P2 hybrid module case study is used to show the benefits and challenges of the axial topology when compared to the radial one. The cooling system of the machine is presented in order to show how the integration of coolant passages could be achieved. The possibility of introducing heat barriers into a hybrid powertrain, decoupling the hybrid module from the rest of the powertrain, is also presented. The predicted performance of the machine is presented and compared to the initial test results. Full article

The mass production of electric vehicles can pressure some specific natural resources that are needed for the production of the motors utilized in such vehicles. In those lines an alternative to the use of rare-earth magnets in the propulsion system is to substitute permanent-magnet synchronous machines (PMSM) by switched reluctance motors (SRM). One of the main drawbacks of SRMs is the torque ripple and consequently the noise and vibration that it can cause in the driveline. The further development of this motor technology needs to properly understand and address the mechanical vibrations caused by the magnetic forces in the stator. The goal of this paper is to investigate the effects of increased complexity of structural modelling in capturing the physical phenomena that governs this system. By comparing the modal parameters of structures modelled by 2D analytical techniques, finite elements (FE) with isotropic material and FE with orthotropic properties, it is possible to discuss the limitations and applicability of each technique. Full article

As previously reported [1-3], ArcelorMittal has a specific electrical steel product line for core laminations, which optimises the performance for automotive traction electrical machines. This iCARe^® product family consists of Save grades allowing for higher efficiency, Torque grades allowing for higher torque density and Speed grades for high speed rotors. The iCARe^® electrical steels now have been developed towards further loss reduction and polarisation increase. This paper shows the improved machine performance achievable by using these new iCARe^® grades. Automotive traction machines require high power density, high efficiency and high torque, to maximise the powertrain’s performance and minimise the use of battery power. Permanent magnet synchronous machines (PMSM) are the preferred choice for electric and hybrid vehicles. When searching for cost reduction via eliminating the need for permanent magnets, wound rotor synchronous machines (WRSM) are an alternative. In this paper, a material comparison study is presented for both a PMSM and a WRSM having the same nominal speed and rated mechanical power. The reference case uses M330-35A electrical steel. The impact of switching to either Save or Torque grades of the latest generation is compared numerically: to determine the efficiency of each combination of machine topology and lamination type, the ArcelorMittal loss model is used [4], an extension of Bertotti’s loss model [5]. The impact of each grade is checked by varying the stack height whilst keeping the output power level constant. Hence the bill of materials is affected, reflecting the amount of active materials (laminations, magnets, windings) needed within each machine type, depending on the chosen electrical steel grade. The results show the efficiency benefits when using low loss Save grades and the torque density benefits when using Torque grades. Moreover, the new Torque grades with lower losses present a new potential for further machine performance enhancement: for instance the Torque 27 grade combines outstanding increase of torque density with high efficiency. Full article