Direct Yaw Moment Control for Distributed Drive Electric Vehicle Handling Performance Improvement

For a distributed drive electric vehicle（DDEV） driven by four in-wheel motors, advanced vehicle dynamic control methods can be realized easily because motors can be controlled independently, quickly and precisely. And direct yaw-moment control（DYC） has been widely studied and applied to vehicle stability control. Good vehicle handling performance： quick yaw rate transient response, small overshoot, high steady yaw rate gain, etc, is required by drivers under normal conditions, which is less concerned, however. Based on the hierarchical control methodology, a novel control system using direct yaw moment control for improving handling performance of a distributed drive electric vehicle especially under normal driving conditions has been proposed. The upper-loop control system consists of two parts： a state feedback controller, which aims to realize the ideal transient response of yaw rate, with a vehicle sideslip angle observer; and a steering wheel angle feedforward controller designed to achieve a desired yaw rate steady gain. Under the restriction of the effect of poles and zeros in the closed-loop transfer function on the system response and the capacity of in-wheel motors, the integrated time and absolute error（ITAE） function is utilized as the cost function in the optimal control to calculate the ideal eigen frequency and damper coefficient of the system and obtain optimal feedback matrix and feedforward matrix. Simulations and experiments with a DDEV under multiple maneuvers are carried out and show the effectiveness of the proposed method： yaw rate rising time is reduced, steady yaw rate gain is increased, vehicle steering characteristic is close to neutral steer and drivers burdens are also reduced. The control system improves vehicle handling performance under normal conditions in both transient and steady response. State feedback control instead of model following control is introduced in the control system so that the sense of control intervention to drivers is relieved.

GENERALIZED TRANSFER FUNCTION OF CONTROL SYSTEM AND AN IMPROVEMENT ON THE DECISION METHOD OF MOVEMENT STABILITY

In this paper the definitions of generalized transfer functios of control system and itscontinuity are presented.Using generalized transfer function as a tool,a set of theorems fordeciding movement stability have been constructed.Thus basing understanding of thecharacteristics of a control dynamics system on its measured procedure will simplify thedecision method of movement stability problems.

Automatic SOC Equalization Strategy of Energy Storage Units with DC Microgrid Bus Voltage Support

In this paper,an improved sag control strategy based on automatic SOC equalization is proposed to solve the problems of slow SOC equalization and excessive bus voltage fluctuation amplitude and offset caused by load and PV power variations in a stand-alone DC microgrid.The strategy includes primary and secondary control.Among them,the primary control suppresses the DC microgrid voltage fluctuation through the I and II section control,and the secondary control aims to correct the P-U curve of the energy storage system and the PV system,thus reducing the steady-state bus voltage excursion.The simulation results demonstrate that the proposed control strategy effectively achieves SOC balancing and enhances the immunity of bus voltage.The proposed strategy improves the voltage fluctuation suppression ability by approximately 39.4%and 43.1%under the PV power and load power fluctuation conditions,respectively.Furthermore,the steady-state deviation of the bus voltage,△U_(dc) is only 0.01–0.1 V,ensuring stable operation of the DC microgrid in fluctuating power environments.

Improving Plasma Confinement by Controlling Hard X-Ray

Since runaway electrons and magnetohydrodynamics activity can contribute to serious damage and energy losses in tokamaks, the effect of an external electric field on runaway electrons and hard x-ray spectra is investigated. Parameters such as the plasma current, the hard x-ray photons count and the mean energy of runaway electrons are measured. Positive and negative voltages of 300 V are applied at lOms after the plasma initiation （while the plasma is forming）, at 15ms （while the plasma is stable） and at 20ms （while the plasma is fading away） to attain the most effective time of applying the external electric field. The number of hard x-ray photons has the most changes in the range of O-200 keV when the external electric fields are applied. Also in the duration of 20-30ms of plasma the greatest number of hard x-ray spectra is detected. When the external electric fields are applied, the mean energy of runaway electrons reduces significantly, especially at 15 ms （while the plasma is stab/e）.

How Can Macroeconomic Control Be Improved?

Ⅰ.New macroeconomic controls not fully realised China introduced a new set of macroeconomic controls in 2004 in an attempt to control excessive growth.Due to the impact of the Asian Financial Crisis, China’s economy grew at a low growth rate between 1998 and 2001.However it accelerated from 2002 onwards,and saw a GDP increase of 11%in the fourth quarler of 2003,a historical high since 1997

Systems model-guided rice yield improvements based on genes controlling source, sink, and flow

A large number of genes related to source, sink,and flow have been identified after decades of research in plant genetics. Unfortunately, these genes have not been effectively utilized in modern crop breeding. This perspective paper aims to examine the reasons behind such a phenomenon and propose a strategy to resolve this situation. Specifically, we first systematically survey the currently cloned genes related to source, sink, and flow;then we discuss three factors hindering effective application of these identified genes, which include the lack of effective methods to identify limiting or critical steps in a signaling network, the misplacement of emphasis on properties, at the leaf, instead of the whole canopy level,and the non-linear complex interaction between source,sink, and flow. Finally, we propose the development of systems models of source, sink and flow, together with a detailed simulation of interactions between them and their surrounding environments, to guide effective use of the identified elements in modern rice breeding. These systems models will contribute directly to the definition of crop ideotype and also identification of critical features and parameters that limit the yield potential in current cultivars.

A strategy for population pharmaceutical quality assessment based on quality by design

From a regulatory perspective,drug quality consistency evaluation must concern different processes used for the same drug.In this study,an assessment strategy based on quality by design(QbD)was developed for population pharmaceutical quality evaluation.A descriptive analysis method based on QbD concept was first established to characterize the process by critical evaluation attributes(CEAs).Then quantitative analysis method based on an improved statistical process control(SPC)method was established to investigate the process indicators(PIs)in the process population,such as mean distribution,batch-to-batch difference and abnormal quality probability.After that rules for risk assessment were established based on the SPC limitations and parameters.Both the SPC parameters of the CEAs and the risk of PIs were visualized according to the interaction test results to obtain a better understanding of the population pharmaceutical quality.Finally,an assessment strategy was built and applied to generic drug consistency assessment,process risk assessment and quality trend tracking.The strategy demonstrated in this study could help reveal quality consistency from the perspective of process control and process risk,and further show the recent development status of domestic pharmaceutical production processes.In addition,a process risk assessment and population quality trend tracking provide databased information for approval.Not only can this information serve as a further basis for decisionmaking by the regulatory authority regarding early warnings,but it can also reduce some avoidable adverse reactions.With continuous addition of data,dynamic population pharmaceutical quality is meaningful for emergencies and decision-making regarding drug regulation.

Comparisons and Improvements of Key Operating Characteristics of Current Source Converter Applied in HVDC System

Because of its controlled power factor and no commutation failure,current source converter(CSC)made up of reverse-blocking IGCTs(RB-IGCTs)offers broad application prospects in the field of HVDC system.Valve voltage and power operating range as the most important operating characteristics should be paid attention to but they are always contradictory.First,the relationship between valve voltage and modulation index is obtained.In particular,valve voltage of converter under the three typical modulation methods is compared,analyzed,and verified.Second,with the help of the independent control strategy and coordinated control strategy of both ends,power operating ranges of the three modulation methods are comprehensively analyzed and compared.Third,in order to solve power coupling at a low active power,the improved coordination control strategy at both ends in this paper is proposed and the relationships among active power,reactive power,DC current and phase angle difference are given in detail.Finally,a 500 kV/3 kA simulation system was built in PSCAD/EMTDC to obtain comparison results of the key operating characteristics of CSC under different modulation methods and the converter can realize unity power operation under random active power after adopting the improved coordinated control strategy,and DC current does not decrease to zero,verifying effectiveness of the coordinated control strategy.

Cascaded navigation control for agricultural vehicles tracking straight paths

In precision agriculture(PA),an agricultural vehicle navigation system is essential and the navigation control accuracy is important in this system.As straight path tracking is the major operating mode of agricultural vehicles on large fields,a cascaded navigation control method for straight path tracking is proposed in this study.Firstly,a cascaded navigation control structure for the agricultural vehicle was discussed.Based on this structure,the navigation control task was decomposed into two cascaded control tasks,namely,the path tracking control task and the steering control task.Secondly,a relative kinematics model of agricultural vehicles was deduced,and an optimal Proportional-Derivative(PD)method based on the deduced model was developed in the path tracking control task.Then,an improved PD method based on a transition process was proposed in the steering control task to enhance the performance of the steering control subsystem.Finally,the effectiveness and the superiority of the proposed method were verified by a series of experiments.Results of the experimental data analysis show that mean value of the lateral position deviation is 0.02 m and standard deviation of the lateral position deviation is 0.04 m,which proves that the proposed method has achieved satisfactory effects on the straight path tracking of agricultural vehicles.

Active Collision Avoidance System Design Based on Model Predictive Control with Varying Sampling Time

In active collision avoidance,the trajectory tracking controller determines the deviation from the reference path and the vehicle stability.The main objective of this study was to reduce the tracking error and improve the tracking performance in collision avoidance.Unlike the previously proposed model predictive control(MPC)strategies with constant sampling time,an improved MPC controller with varying sampling time based on the hierarchical control framework was proposed in this paper.Compared with the original MPC tracking controller,the improved MPC controller demonstrated better adaptive capability for the varying road adhesion coefficients and vehicle speed on a curved road.The simulation results revealed that the hierarchical control framework generated an optimal trajectory for collision avoidance in real-time by minimizing the potential field energy.

An improved ET control method to determine the water-saving potential for farmland in Baiyangdian Watershed, China

Resource-based water-saving potential has been recognized as the reduction of evapotranspiration and water loss of inefficient irrigation systems. In this paper, an improved evapotranspiration control model is applied to calculate resource-based water-saving potential, considering the influences of effective rainfall （uncontrolled evapotranspiration） and irrigated water （controlled evapotranspiration）. Farmland in Baiyangdian Watershed, a highly productive area in northern China, is analyzed to determine the water-saving potential of irrigation processes. The water-saving potential was zero, 163.90 × 10^6m3, and 318.24 × 10^6m3 in wet, normal, and dry years, respectively, and was greater in years with less rainfall. Under the combined effect of rainfall, crop water consumption, and crop water requirements, the water-saving potential showed obvious temporal and spatial variations. July and August comprised almost 98.6% of the annual potential. In the northeast and southwest corner of the study area, potential approached zero. The potential was 1.53 times greater in the north-central than in the south-central area. The model can furnish the appropriate timing and region to water managers for implementing water-saving strategies.

Analysis and Design of Vector Control for VSC-HVDC Connected to Weak Grids

Voltage source converter based high voltage direct current transmission(VSC-HVDC)is considered one of the most suitable technologies to integrate renewable energies.However,connecting VSC to a weak grid is challenging since traditional vector control tends to become unstable under high power demand conditions.In this paper,an improved vector control method is proposed wherein a feed forward branch based on steady state and small signal analysis of the VSC system is added under weak grid situations.The feed forward branch promotes faster reactive power response,thus enhancing the stability of the VSC system.Since the improved vector control uses the same inner loop as traditional vector control,the proposed method allows for the ability to retain fault current suppression capabilities.Furthermore,the control parameters of the outer loop of the improved vector control need not vary according to the variation of the operating points,which makes it easy to implement.The feed forward branch is implemented by solving a nonlinear equation or through use of a look-up table.The influence of the estimation errors of short circuit ratio(SCR)on the control performance is also studied.The effectiveness of the improved vector control is demonstrated through small signal model analysis and time domain simulations.

Droop Control Method to Achieve Maximum Power Output of Photovoltaic for Parallel Inverter System

In general,the power distribution of a parallel inverter is achieved by the use of droop control in a microgrid system,which consists of PV inverters and non-regeneration energy source inverters without energy storage devices in an islanded mode.If the shared load power is no more than the available maximum PV inverter output power,then there is a power waste for the PV inverter.In addition,due to the intermittency of PV sources,the system may become unstable if the shared load power is more than the available maximum power output of the PV(MPO-PV)inverter.Therefore,in order to avoid power waste and potential instability caused by insufficient PV power by traditional droop control,this paper recommends an improved droop control scheme to maximize the power output of PV units.As required by the load,the remaining power is composed of the other inverters,which can effectively improve the utilization rating of renewable energy sources and system stability.At the same time,according to the system stability analysis based on small signal modeling,it has been designed around the droop coefficients of the improved droop control loop.In the end,the simulation and experimental results show that the suggested scheme has a varied validity and robustness.

Design of variable-rate liquid fertilization control system and its stability analysis

Variable-rate technology(VRT)has been paid more attentions by farmers in an attempt to match inputs to local growing conditions efficiently.Farmers in every country are highly encouraged to adopt this practice rather than uniform-rate application(URA).However,the standard methods and design used to quantify application accuracy for VRT remain lacking.Therefore,a variable-rate liquid fertilization control system was designed to meet accurate fertilization demand.The designed control system could enable the real-time proportion and mixture of three kinds of liquid fertilizers,namely,N,P and K,in accordance with decision support subsystem.The task controller reads related information and sends such data to the control system,which is responsible for fertilization operation.The controller could realize liquid fertilizer adjusting through the electromagnetic flow control valves.A high-precision flow meter could measure the fertilization amount,which is sent as feedback to the controller to form a closed-loop control system based on the improved proportional-integral-derivative(PID)control algorithm that could enhance the stability and accuracy of precision variable-rate liquid fertilization control systems.Comparisons between the actual and planned application rates indicated good performance for both static and field experimental trials.Mathematical models and transfer functions for some functional modules were then constructed by classical theories to derive a system characteristic equation.To verify the static and dynamic performances,the control system was simulated using the Simulink module on Matlab.Results showed that the variable-rate fertilization was in accordance with the planned data and that the signal trace effect was good.The error was less than 5%for fertilization amount and fertilizer proportion,respectively,and the control response time was 6 s.

Data Driven Model-Free Adaptive Control Method for Quadrotor Trajectory Tracking Based on Improved Sliding Mode Algorithm

In order to solve the problems of dynamic modeling and complicated parameters identification of trajectory tracking control of the quadrotor,a data driven model-free adaptive control method based on the improved sliding mode control(ISMC)algorithm is designed,which does not depend on the precise dynamic model of the quadrotor.The design of the general sliding mode control(SMC)algorithm depends on the mathematical model of the quadrotor and has chattering problems.In this paper,according to the dynamic characteristics of the quadrotor,an adaptive update law is introduced and a saturation function is used to improve the SMC.The proposed control strategy has an inner and an outer loop control structures.The outer loop position control provides the required reference attitude angle for the inner loop.The inner loop attitude control ensures rapid convergence of the attitude angle.The effectiveness and feasibility of the algorithm are verified by mathematical simulation.The mathematical simulation results show that the designed model-free adaptive control method of the quadrotor is effective,and it can effectively realize the trajectory tracking control of the quadrotor.The design of the controller does not depend on the kinematic and dynamic models of the unmanned aerial vehicle(UAV),and has high control accuracy,stability,and robustness.