To improve vehicle handling performance, a variable steering ratio characteristic for steer-by-wire system is designed. The steering ratio is adjusted by a compensating coefficient according to vehicle longitudinal speed and steering wheel angle. To evaluate the performance of vehicle with variable steering ratio, simulations are conducted based on an objective evaluation index, which consists of quadratic cost functions of vehicle lateral deviation, steering angular speed, vehicle lateral acceleration and roll angle. By using the optimized data from the simulation results, a Takagi-Sugeno fuzzy neural network is designed for the steering ratio control. In order to test and validate the proposed controller, a series of comparison experiments are conducted on a closed-loop driver-vehicle system, including lemniscate curve test and double lane-change test. The results demonstrate that compared with a conventional steering system with fixed steering ratio, the proposed system can not only improve steering agility at low speed and steering stability at high speed, but also reduce driver’s workload in critical driving conditions.

The radiated electromagnetic disturbance was evaluated by measuring the electric field intensity in a bandwidth of 10 kHz-2.75 GHz near the valve hall, direct-current (DC) area, reactor room, and transformers in a ±320-kV modular multilevel converter-based high-voltage, direct-current (MMC-HVDC) converter station. In addition, the distribution of electric field intensity was analyzed in various regions in the converter station. According to the law of electric fields attenuation with distance, the radiated electric field intensities at the position 200 m away from the converter station was calculated by using the electric fields measured in the converter station. The results show that the levels of radiated disturbance inside and outside the converter station meet the standards' requirements. The amplitude spectra of the electric field intensity in a traditional HVDC system and MMC-HVDC system were compared. Finally, the mechanism for radiated electromagnetic interference of the MMC-HVDC converter system was analyzed from the aspects of disturbance source characteristics, wall shielding and radiated structure. INDEX TERMS ±320 kV MMC-HVDC, radiated disturbance, intrinsic characteristics, mechanism of radiation.

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