Compound Power-split Hybrid Research Articles

Development of a Compound Power-split Hybrid Power System for Commercial Vehicles

Development of a Compound Power-split Hybrid Power System for Commercial Vehicles

Multivariable predictive functional control of a compound power-split hybrid electric vehicle

The Corun hybrid system (CHS) is a deeply coupled multiple-input–multiple-output (MIMO) hybrid system. The two inputs are the torques of the two motors. The two outputs are the carrier speed and transmission output torque. Using the traditional control method, the multi-objective control quality cannot be guaranteed because of the adopted static decoupling method and proportional–integral–derivative (PID) controllers. In this paper, the problems of the traditional control method are carefully analyzed, and a new control method is proposed. Instead of static decoupling, dynamic decoupling is adopted to improve the decoupling control effect. A predictive functional controller instead of a PID controller is adopted to deal with the pure delay caused by controller area network (CAN) communication. The tracking effect of the target value is further improved by predictive functional controllers. For the two decoupled subsystems, that is, the integral system and the second-order underdamped system, two predictive functional controllers are designed. The new control method was verified by simulations and tests. The results show that the new control method is superior to the traditional control method for CHS.

Configuration Design and Optimization of a Novel Two-Mode Compound Power-Split Hybrid System

Configuration Design and Optimization of a Novel Two-Mode Compound Power-Split Hybrid System

Multivariable model predictive control of a compound power-split hybrid electric vehicle during the tip-in/out process

For a compound power split hybrid system, such as the Corun hybrid system (CHS), a frequently encountered problem is determining how to compensate for the inertia torque of the transmission via the torque distribution of the two motors. The equivalent inertia of the transmission is variable and depends on the angular acceleration. According to the traditional control scheme, the target torque of the motors is distributed by simplifying the output angular acceleration to 0. This simplification introduces deviations in the torque distribution, and it is difficult to guarantee the quality of the two control quantities simultaneously. Recent research has also focused only on the control quality of one of the outputs. To solve this problem, a direct MIMO control scheme is proposed in this paper that directly calculates the target torques of the two motors based on control deviations. A multivariable model predictive controller (MPC) was designed for the control of transient processes. The simulation results showed that the proposed control method can improve the control accuracy of two objectives significantly, and it has an excellent ability to reject torque disturbances.

Control optimization of a compound power-split hybrid power system for commercial vehicles

In this paper, based on two planetary gear sets, a novel compound power-split hybrid power system for commercial vehicles is presented. Firstly, mathematical models of the system dynamic torque control and the system efficiency are established by using an equivalent lever diagram and analyzing the power flow respectively. Then the system operating modes which are divided into two pure electric modes and one hybrid mode and corresponding control strategies are analyzed by the combined lever diagrams. Finally, control strategies in different modes to looking for the optimal system efficiencies are designed and validated by the bench test. In order to prolong its service life, the battery is charged with small power in the hybrid mode. The design and test results indicate that the optimal system efficiency control strategies are reasonable and reliable. The maximum value of the optimal system efficiency can reach about 0.92 in the pure electric mode, and 0.39 in the hybrid mode. And the proportion of the engine operating points with the brake specific fuel consumption (BSFC) lower than 215 g/kWh is 81%. The co-simulation results show that the maximum system efficiency can achieve 14.9% fuel consumption per 100 km drop compared with the minimum system efficiency for an 80 km/h constant speed condition, which indicates that the optimal system efficiency control strategy can greatly improve the vehicle fuel economy. This study can offer a research direction for energy management of hybrid power systems.

Experimental and Characteristic Analysis during the Engine Start-Up Process for a Compound Power-Split Hybrid Electric Vehicle

Experimental research is essential in the development of a hybrid electric vehicle. In this study, a bench test was conducted for a compound power-split hybrid electric vehicle (PSHEV) to analyze the real dynamic characteristics of its components and the factors of system shock and vibration during the engine start-up process. Firstly, the mode switching process with an engine start-up was divided into four stages by the lever method. The basic control strategy of mode switching with engine start-up was formulated and tested on a bench test platform. Secondly, based on the bench test data, the output characteristics of the battery motor, engine, and driveshaft were analyzed in detail. The main variable parameters of the engine control unit were investigated in the engine start-up process. Ultimately, the results showed that the engine’s pulsating torque was the main reason for system jerk and vibration during the engine start-up process, and the excessive intake manifold pressure before the engine’s ignition was one of the main reasons for the large output torque ripple. When initiating the electric engine starting process, the jerk and vibration presented a wide fluctuation. The maximum value of the equivalent jerk was 92.12 m/s3, and the maximum value of the absolute value of the vibration acceleration was 4.077 m/s2.

Research on modelling and simulation of single-mode power split hybrid system

Aiming at an optimised single-mode compound power split hybrid system, the main operating mode of the hybrid system and the torque control strategy were developed in this paper. LMS/AMESim was used to establish the plant model of the vehicle as well as the key components of the hybrid system, while the vehicle control model was established in Matlab/Simulink. In addition, the fuel economy of a certain SUV under the NEDC road spectrum was simulated by the co-simulation model, and the simulation results were compared with the experimental results on the auto chassis dynamometer. The results demonstrated that the established simulation model is an accurate reflection of the physical reality under different road spectrum conditions. Application of the model can greatly reduce the difficulty of control strategy design and improve the efficiency of vehicle development.

Research on modelling and simulation of singlemode power split hybrid system

Aiming at an optimised single-mode compound power split hybrid system, the main operating mode of the hybrid system and the torque control strategy were developed in this paper. LMS/AMESim was used...

Torque ripple compensation control for hybrid UGVs in mode transition based on current harmonic control of a PMSM

Load jumping and mode transitions both cause the unstable dynamic states for compound power-split hybrid Unmanned Ground Vehicles (UGVs), and these phenomena lead to vibrations of the transmission system and longitudinal buffeting of the vehicle. This study presents a feed-forward compensation control strategy for load jumping and mode transitions to reduce the corresponding torsional vibration in hybrid UGVs. The proposed method injects an appropriate harmonic current into a permanent magnet synchronous motor (PMSM) to generate a harmonic torque that is opposite to the load torque, which improves the dynamic response quality of the vehicle load. First, the multimode structure of a hybrid UGV and mode switching vibration and shock are investigated, as well as a feed-forward compensate control architecture is proposed. Second, two models are established the PMSM dynamic model based on the electromagnetic coupling principle and a 2-degree-of-freedom torsional vibration model of transmission system by simplifying the vehicle system. Third, the harmonic current injection method is proposed, and the harmonic current equation is derived. Based on the field-oriented control algorithm, a double closed-loop controller is designed for the torque and speed of the PMSM, and the internal model control method is applied to design the current controller. The simulation results show that the proposed strategy effectively suppresses jerk and that the harmonics current transfers the energy from the mechanical vibrations of the system into electric power fluctuations.

Estimation of Transmission Input&Output Shaft Torque and Drive Wheel Speed for Compound Power Split Powertrain Based on Unknown Input Observer

Precise estimation of transmission input&output shaft torque and wheel speed is significant to the development of torque distribution and coordinated control method for the power split hybrid powertrain system. This paper studies an estimation method of transmission input and output torque as well as drive wheel speed using an unknown input observer in different operating modes for a compound power split hybrid powertrain system. Firstly, the configuration and dynamic characteristic of power split transmission is analyzed. Then, state equations in different operating modes are established, and a Takagi-Sugeno (T-S) fuzzy model is utilized to deal with the nonlinearities of load resistance torque. Furthermore, an unknown input reduced-order observer is designed to estimate the transmission input&output shaft torque and wheel speed. The asymptotical stability of the developed observer is verified based on Lyapunov theory. Finally, the performance of the unknown input observer is assessed by comparing with the Luenberger observer based on Matlab/Simulink simulation platform and test bench. Simulation and experiment results show that, the proposed observer can estimate the transmission input&output shaft torque and wheel speed more effectively in different operating modes.

Modeling and Dynamic Response Analysis of a Compound Power-Split Hybrid Electric Vehicle During the Engine Starting Process

This study is aimed at revealing the dynamic response characteristics of a power-split hybrid electric vehicle (HEV) during the mode transition process with the engine starting. In this paper, for a hybrid powertrain system whose engine is directly connected to a compound power-split transmission, the equivalent lever method is first used to analyze the mode transition process with the engine starting. Then, based on the theoretical formulations and lookup tables, a dynamic model of the compound power-split HEV is established in detail, taking into consideration the engine ripple torque, battery-motor characteristics, dynamic meshing force between gears, and shaft spring-damping characteristics. The powertrain dynamic model is verified by a bench test. Moreover, taking the vehicle jerk and engine starting time as the evaluation indexes of the dynamic response characteristics, the influencing factors of the dynamic response characteristics in the engine starting process are analyzed comprehensively from the aspects of the engine, battery-motor, and engine starting condition. Finally, the engine starting process is synthetically optimized based on the obtained impact law of different influencing factors. The simulation results show that the synthesis optimization method can effectively reduce vehicle jerks and the engine starting time and improve driving comfort during the engine starting process.

Model Predictive Control of Engine Start-up for Compound Power-split Hybrid Powertrain

Model Predictive Control of Engine Start-up for Compound Power-split Hybrid Powertrain

Robust hierarchical estimator of clutch torques for a compound power-split hybrid electric vehicle

Abstract A hierarchical estimator for a compound power-split hybrid electric vehicle is proposed herein to individually observe interacted clutch torques. It consists of reference layer and estimation layer, and combines several classical observers. The estimator utilizes less nonlinear parameters in clutch assembly by introducing torque estimations from unknown input observers into update laws, and forms a closed-loop structure to better achieve system robustness through interactive feedbacks from each other. Uncertainties of estimation model and disturbances of real system are considered and introduced into the analysis of input-to-state stability. As a result, an algorithm of gain matrix optimization is obtained in the form of linear matrix inequality. Results from platform simulations and real car tests demonstrated that it improves overall performance of steady accuracy and fast response, and obtains excellent robustness for the complicated hybrid system.

Robust optimisation of dynamic and NVH characteristics for compound power-split hybrid transmission

In this paper, vibro-acoustic characteristics of a power-split hybrid transmission including a compound planetary gear set are investigated by numerical procedure and refined system dynamics modelling. For validation of the numerical predictions, bench tests are performed for dynamic and acoustic responses of the hybrid transmission, contribution rates of acoustic radiation power induced due to the planetary gears, support bearings, transmission shafts and the gearbox housing are estimated. In improving the noise, vibration and harshness (NVH) performance of the transmission during hybrid vehicle acceleration, traction torques of the motors against the planetary gear parametric resonance are formulated and an optimal control strategy is proposed. By real road NVH test results acquired on board of the midsize hybrid car, it is demonstrated that a significant reduction of the planetary gear whine noise is achieved. As a result, numerical approaches applied to establish relationships between torques of the two traction motors and parametric excitations of the compound planetary gear train are experimentally validated.

Investigation of mode transition coordination for power-split hybrid vehicles using dynamic surface control

For passenger cars propelled by the dedicated compound power-split hybrid powertrain, driveline oscillations-induced vehicle jerks are often excited during clutch-to-clutch shift operations while drive mode changes. To tackle this issue, a coordinated dynamic surface control is developed by integrating clutch slips and motor torque compensation strategies through trajectories tracking of both clutch slip speed and wheel speed. Uncertainties or disturbances are treated to be additional inputs of the system, and model nonlinearities are considered and implemented in discretized form through lookup tables. A complex simulation model including electro-hydraulic system is proposed and validated via experiments. The coordinated controller is validated by collaborative simulation. Numerical examples are made and simulation results verify that the controller is effective and robust enough against parameters uncertainties.

Engine start-up optimal control for a compound power-split hybrid powertrain

Abstract Engine start-up is the key for the control of mode transition from electric drive mode to electronic-Continuously Variable Transmission (e-CVT) mode for a compound power-split hybrid electric vehicle (HEV). With the engine shaft directly connected to the powertrain through a torsional damper spring (TDS), the engine ripple torque (ERT) before ignition is amplified by the powertrain and transmitted to the wheel, which has a significant impact on the vehicle. To improve the ride comfort of the mode transition process, an engine start-up control strategy is proposed. First, the ERT model and the dynamic model of power-split powertrain were built, and the mode transition process was analyzed. Second, an optimal crank track of engine speed was designed based on the dynamic programming aiming at ride comfort. Third, the engine reference acceleration curve was calculated according to the optimal speed track, and an optimal engine start-up control strategy was proposed. Finally, through simulations of the dynamic programming the influence factors for engine start-up were examined, and the experiment results indicate that the proposed engine start-up optimal control can effectively improve the ride comfort during mode transition.

Dynamic coordinated control during mode transition process for a compound power-split hybrid electric vehicle

Abstract The fuel economy of the hybrid electric vehicles (HEVs) can be effectively improved by the mode transition (MT). However, for a power-split powertrain whose power-split transmission is directly connected to the engine, the engine ripple torque (ERT), inconsistent dynamic characteristics (IDC) of engine and motors, model estimation inaccuracies (MEI), system parameter uncertainties (SPU) can cause jerk and vibration of transmission system during the MT process, which will reduce the driving comfort and the life of the drive parts. To tackle these problems, a dynamic coordinated control strategy (DCCS), including a staged engine torque feedforward and feedback estimation (ETFBC) and an active damping feedback compensation (ADBC) based on drive shaft torque estimation (DSTE), is proposed. And the effectiveness of this strategy is verified using a plant model. Firstly, the powertrain plant model is established, and the MT process and problems are analyzed. Secondly, considering the characteristics of the engine torque estimation (ETE) model before and after engine ignition, a motor torque compensation control based on the staged ERT estimation is developed. Then, considering the MEI, SPU and the load change, an ADBC based on a real-time nonlinear reduced-order robust observer of the DSTE is designed. Finally, the simulation results show that the proposed DCCS can effectively improve the driving comfort.

STUDY ON DYNAMIC CHARACTERISTICS OF ELECTROMECHANICAL COUPLING IN MODE SWITCHING PROCESS OF MULTI-POWER TRANSMISSION SYSTEM CONSIDERING INTERNAL AND EXTERNAL EXCITATION

The compound power-split hybrid transmission system is usually driven by the internal and external excitation to cause the impact or vibration of the transmission system. In this paper, a pure torsional nonlinear dynamic model of electromechanical coupling is established for a compound power-split hybrid transmission system. The dynamic torques outputted by the power sources are used as the external excitation of the planetary gear power coupling mechanism, the meshing shocks caused by gear backlash in the gear mechanism are taken as the internal excitation. From the perspective of elastic dynamics, the influence on the dynamic characteristics of the electromechanical system is analyzed by considering the interaction of internal and external excitation during the mode switching from the pure electric mode to the hybrid mode. The results show that, with the decrease of the dynamic torques of motors, the external excitation will cause the internal excitation in the form of meshing impact between the planetary gears and the sun gears. The influence of the interaction of the internal and external excitation on the mechanical properties of the dynamic coupling mechanism increases with the increase of the gear backlash. However, the influence on the dynamic characteristics of power sources is not obvious.

Mode transition coordinated control for a compound power-split hybrid car

With a compound power-split transmission directly connected to the engine in hybrid cars, dramatic fluctuations in engine output torque result in noticeable jerks when the car is in mode transition from electric drive mode to hybrid drive mode. This study designed a mode transition coordinated control strategy, and verified that strategy’s effectiveness with both simulations and experiments. Firstly, the mode transition process was analyzed, and ride comfort issues during the mode transition process were demonstrated. Secondly, engine ripple torque was modeled using the measured cylinder pumping pressure when the engine was not in operation. The complete dynamic plant model of the power-split hybrid car was deduced, and its effectiveness was validated by a comparison of experimental and simulation results. Thirdly, a coordinated control strategy was designed to determine the desired engine torque, motor torque, and the moment of fuel injection. Active damping control with two degrees of freedom, based on reference output shaft speed estimation, was designed to mitigate driveline speed oscillations. Carrier torque estimation based on transmission kinematics and dynamics was used to suppress torque disturbance during engine cranking. The simulation and experimental results indicate that the proposed strategy effectively suppressed vehicle jerks and improved ride comfort during mode transition.

Development of a Plug-In HEV Based on Novel Compound Power-Split Transmission

In order to extend the product applications into plug-in hybrid electric vehicle field, a high capacity lithium-ion battery is configured and matched to the previous compound power-split hybrid transmission which is based on a modified ravigneaux gear set with two additional brake clutches. The equivalent lever diagrams are used to investigate the operating modes for the hybrid system, and its dynamic and kinematic characteristics in equations are derived. To evaluate the economy and power performance of the plug-in hybrid vehicle, a forward-looking simulation platform and components model are established. In addition, the simulating results of key power and economy tests are demonstrated. Results show that the proposed powertrain configuration can be well used for plug-in applications, and the economy and power performance can be further improved.