Ji Xuewu

A modified structure internal model robust control method for the integration of active front steering and direct yaw moment control

Taking into account the nonlinearity of vehicle dynamics and the variations of vehicle parameters, the integrated control strategy for active front steering (AFS) and direct yaw control (DYC) that can maintain the performance and robustness is a key issue to be researched. Currently, the H∞ method is widely applied to the integrated control of chassis dynamics, but it always sacrifices the performance in order to enhance the stability. The modified structure internal model robust control (MSIMC) obtained by modifying internal model control (IMC) structure is proposed for the integrated control of AFS and DYC to surmount the conflict between performance and robustness. Double lane change (DLC) simulation is developed to compare the performance and the stability of the MSIMC strategy, the PID controller based on the reference vehicle model and the H∞ controller. Simulation results show that the PID controller may oscillate and go into instability in severe driving conditions because of large variations of tire parameters, the H∞ controller sacrifices the performance in order to enhance the stability, and only the MSIMC controller can both ensure the robustness and the high performance of the integrated control of AFS and DYC.

A new inverter compensation strategy based on adjusting dead-time on-line

This paper proposes a new dead-time compensation technique for minimizing current distortion of permanent magnet synchronous motor (PMSM). Conventional dead-time compensation techniques for space vector PWM (SVPWM) are based on the fact that inverter dead-time is fixed, and need current direction information to eliminate dead-time effects correctly. In this paper, a new method which independently adjusts each dead-time of three inverter legs on-line according to the value of corresponding phase current is developed. The new means leads the dead-time disturbance voltage vector to rotate synchronously with current vector and no longer depends on current direction. Furthermore, dead-time disturbance voltages in dq frame can be calculated using id and iq while need no current direction knowledge. The experimental results validate that the new algorithm can minimize the phase current distortion.

Field weakening control of PMSM used in an electric power steering system

Presently, the direct current motor is widely used as an actuator in electric power steering system (EPS) for compact cars. When it comes to mid-size saloons, the permanent magnet synchronous motor (PMSM) is more suitable for numerical advantages. To acquire the smooth steering feeling, the motors torque and speed should match well. However, the rated speed of the motor used in EPS is usually round 1000r/min, while under the condition of fast operating steering wheel the motor speed may be higher than 2500r/min. Therefore, it is necessary to carry out field weakening control of PMSM. In most cases, the stators resistance is ignored when the field weakening control strategy is carried out. However, the stators resistance should be taken into consideration in EPS application for high current and low voltage. This paper proposes a novel field weakening law of PMSM with consideration of motor stator resistance. The proposed law is verified by experiments on EPS test bench. And it is found that the heavy steering feeling problem under the fast operating steering wheel condition is solved by using the field weakening law proposed in this paper.

Phase compensation on EPS

For the purpose of improving the performance of Electric Power Steering System (EPS), phase compensation must be added on the control strategies. Two methods, including speed feedback and differentiation, are discussed in this paper. As to the latter, the emphasis is made on the differences of ideal differentiation and actual one. Simulation results show that the above mentioned methods could obviously increase the stability of EPS system. The control effects are also improved after imbedding the methods to the self-designed EPS system.