•By the characteristic analysis of VSG, the causes and influencing factors of TPAI and FOC are revealed, and the inherent relationship between TPAI and FOC is found.•Based on the phase portrait ...theory, the stability analysis of different influencing factors is carried out. It is found that the proposed method can significantly enhance the TPAS of VSG under serious grid faults.•According to the verification results, the proposed method can simultaneously realize the TPAS and FCS of VSG during the fault, and the virtual inductance based on QSA can effectively suppress IIC. In addition, this method has the advantages of simple operation, no need to freeze the reactive power loop, and strong adaptability to engineering application problems such as considering the change of fault impedance and the difficulty of grid fault voltage measurement.
When a serious grid fault occurs, a virtual synchronous generator (VSG) tends to lose transient power angle stability (TPAS) and cause the fault current to exceed the limit. Most existing research usually neglects the inherent relationship between transient power angle instability (TPAI) and fault over-current (FOC), which leads to the two problems being solved separately rather than simultaneously. In this paper, the transient power angle and fault current characteristics of VSG are first studied, and the causes and influencing factors of TPAI and FOC are explored. Then, the TPAS analysis is carried out based on the phase portrait theory. A TPAS control method for VSG considering fault current suppression (FCS) is proposed. This method is fulfilled by the combined regulation of active power reference and reactive voltage regulation coefficient, in which the reference and coefficient can be adjusted adaptively according to different fault degrees and application scenarios. In addition, a quasi-static approximate (QSA)virtual inductance is introduced to limit the instantaneous inrush current (IIC). The proposed method achieves both the TPAS and FCS at the same time during the fault. Finally, simulations and experiments verify the correctness of the theoretical analysis and the proposed method.
In this article, a novel active front steering (AFS) control strategy including the upper controller and the lower controller is proposed to improve the yaw stability and maneuverability for ...steer-by-wire (SbW) vehicles. The adaptive recursive integral terminal sliding mode (ARITSM) control is adopted in the upper controller for guaranteeing the convergence performance of both the actual sideslip angle and the yaw rate with strong robustness and fast convergence rate. Then, a fast nonsingular terminal sliding mode (FNTSM) control with extreme learning machine (ELM) estimator to estimate its equivalent control is designed in the lower controller to track the desired front wheel steering angle calculated from the upper controller for driving the sideslip angle and the yaw rate to converge ideal value. It is shown that the upper controller takes two controlled variables (vehicle sideslip angle and yaw rate) and only one control input (front steering angle) into consideration, which can obtain a better performance compared with the case of using only one of these values. Since using the ELM technique in the lower controller to estimate the equivalent control of the FNTSM, not only the dependence of SbW system dynamics can be alleviated in the process of designing controller but also the excellent steering control performance can be achieved. Comparative simulations are carried out by utilizing Carsim and Matlab software to validate the excellent performance of the proposed control strategy for different steering maneuvers.
This paper proposes a new coordinated method for preventive generation rescheduling and corrective load shedding to maintain power system transient stability under uncertain wind power variation. A ...two-step bi-level optimization model is proposed where generation rescheduling and load shedding are coordinated by a risk coordination parameter, which adjusts the total coordination cost in the upper level. Then, based on Extended Equal Area Criterion (EEAC) and trajectory sensitivities, the non-linear risk and stability constraints are converted into the linear form for generation rescheduling cost and load shedding cost optimization in the lower level, respectively. Uncertain wind power output is modeled as a small number of robust test scenarios. Finally, the golden section search is applied to solve the bi-level problem. The proposed method is validated on the New-England 39-bus system by using commercial grade software. The computational efficiency, economic optimality, and stability robustness under random wind power of the method are demonstrated.
Coal face spalling is a major issue affecting the safety of a large-cutting-height mining face, especially in deep mining. In order to analyze failure mechanisms and propose corresponding stability ...control measures in a large-cutting-height longwall face, panel 1303, with a mining depth of 860 m, which is arranged and advanced distances of 300 m and over 1000 m along the dip and strike directions of a coal seam, respectively, was selected as the engineering background. In addition to uniaxial compressive strength (UCS) tests, triaxial compression tests under different confining pressures and loading methods were carried out to investigate the deformation characteristics of the coal specimens. A mechanical model, the “coal face support roof”, was established to illustrate the factors affecting the stability of the coal face. Combined with numerical simulation, the dominant factor was obtained, and the stress distribution around the coal face at different advance distances was revealed. Based on the coal face failure mechanism, the pertinent in situ measures of “manila + grouting” reinforcement technology for controlling coal face spalling were proposed. The results showed that the coal face spalling depended mainly on vertical cyclic loading and horizontal unloading in both initial and periodic weighting. In terms of deep mining, the surrounding stress distribution played a vital role in coal face failure and instability. Specifically, two dimensions of loading conditions were found in the front 3 m of the coal face, and the principal stress
σ
xx
of the coal body was significantly less than the other two principal stresses in the front 8 m of the coal face. In addition, the horizontal principal stress σ
yy
was greater than the vertical principal stress σ
zz
. Therefore, the horizontal principal stress and strength of the coal body were the prominent influencing factors in the large-cutting-height coal face. The mining height and support system working resistance were also of great importance with respect to the stability of the coal face to some degree. Lastly, “manila + grouting” reinforcement technology proposed in this study resulted in 70–80% reduced potential for the occurrence of coal face spalling and in the degree of failure of the coal face, as well as grouting cost could be saved of 30–40% compared with pure grouting measures.
Direct yaw moment controllers improve vehicle stability and handling in severe manoeuvres. In direct yaw moment control implementations based on Linear Quadratic Regulators (LQRs), the control system ...performance is limited by the unmodelled dynamics and parameter uncertainties. To guarantee robustness with respect to uncertainties, this paper proposes a gain scheduled Robust Linear Quadratic Regulator (RLQR), in which an extra control term is added to the feedback contribution of a conventional LQR to limit the closed-loop tracking error in a neighbourhood of the origin of its state-space, despite the uncertainties and disturbances acting on the plant. In addition, the intrinsic parameter-varying nature of the vehicle dynamics model with respect to the longitudinal vehicle velocity can compromise the closed-loop performance of fixed-gain controllers in varying driving conditions. Therefore, in this study the control gains optimally vary with velocity to adapt the closed-loop system to the variations of this parameter. The effectiveness of the proposed RLQR in improving the robustness of a classical LQR against model uncertainties and parameter variations is proven analytically, numerically and experimentally. The simulation and vehicle test results are consistent with the formal analysis proving that the RLQR reduces the ultimate bound of the error dynamics.
•Propose a model-free method for transient stability prediction and control.•New stability criteria based on OMIB-ω trajectory is derived from the IEEAC/SIME.•A new trajectory prediction method is ...presented based on E-OS-ELM.•A fast-analytical generator-shedding stability control method is proposed.•Relationship of shedding amount and the latency of PMU environment is illustrated.
Using PMU measurements, this paper proposes a model-free method to predict post-fault transient instability and develop emergency generator-shedding control. First, the multi-machine system is converted to an equivalent one-machine-infinite-bus (OMIB) system based on online generator clustering, and then the stability criteria are derived to judge the transient stability using the OMIB rotor speed (OMIB-ω) trajectory. Next, a new trajectory prediction algorithm based on ensemble online sequential learning machine (E-OS-ELM) is proposed to predict the OMIB-ω trajectory with an adaptive prediction window. The post-fault transient instability status can be detected in advance on basis of the predicted ω trajectory and the derived stability criteria. Lastly, when the system is foreseen to lose stability, an analytical generator-shedding control algorithm is presented, and the relationship between the generator-shedding amount and the time delay is illustrated. Case studies on the New-England 39-bus system, the NPCC 140-bus system and a realistic province power system in China are presented to show the proposed methodology can detect the instability status early, and help the system maintain synchronism.
A conventional robotic wheelchair containing four wheels (two active driving wheels and two passive casters) is statically stable with poor manoeuvrability. In comparison, a two-wheeled robotic ...wheelchair (TWRW) without the support of casters offers much better manoeuvrability but is inherently unstable and requires a stability control. Most stability controllers rely on the driving torques of the wheels which are high in magnitude and result in large energy consumption. Various disturbances in the system also affect the performance of the controller.
To address these problems, this paper presents a novel control approach where the stability control is achieved through the motion of a pendulum-like movable mechanism added to the TWRW. A scaled-down TWRW is designed to evaluate the performances of the controllers based on PID control and second order sliding mode control (SOSMC). Experimental results show that under the proposed controller approach, the stability of the TWRW is achieved with much less torque, power, and energy consumption than the conventional control systems.
Herein, a novel humic acid-Fex+ complex-coated ZVI (HA-Fex+@ZVI) was synthesized and used to activate peroxydisulfate (PDS) for phenol degradation. The HA-Fex+ shell selectively reacted with PDS ...rather than O2, leading to the formation of modified ZVI with excellent surface stability in storage and ultraefficient PDS activation in advanced oxidation processes (AOPs). As a result, the phenol degradation and PDS activation efficiencies of HA-Fex+@ZVI/PDS were ∼14.4 and ∼1.8 times higher than those of ZVI/PDS, respectively. Mechanistic explorations revealed that the replacement of the HA-Fex+ shell relative to the original passivation layer of ZVI greatly changed the SO4•- generation pathway from a heterogeneous process to a homogeneous process, resulting from the slow exposure of Fe0 (generating dissolved Fe2+) and the depolymerized HA (enhancing the Fe3+/Fe2+ cycle). Based on experimental analysis and density functional theory (DFT) calculations, the Fe3+ in HA-Fex+ could be reduced to Fe2+ by PDS, resulting in the disintegration of the HA-Fex+ shell and exposure of Fe0 core active sites. Furthermore, compared to similar catalysts synthesized with commercial HA and traditional chemicals, HA-Fex+@ZVI synthesized with multiple waste biomasses exhibited better performance. This research provides valuable insights for designing ZVI-based catalysts with excellent storage stability and ultraefficient PDS catalytic activity for AOPs.
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•Novel humic acid-Fex+ complex-coated ZVI (HA-Fex+@ZVI) were synthesized.•HA-Fex+ shell of HA-Fex+@ZVI selectively reacted with PDS rather than O2.•PDS could reduce Fe3+ in HA-Fex+, leading to the disintegration of the shell.•HA-Fex+@ZVI showed excellent storage stability and ultraefficient PDS activation.•HA synthesis method could be universally applied to different waste biomasses.
Abstract
In order to reduce the rate of traffic accidents under extreme working conditions and to achieve stability control of the vehicle system under these conditions, a theoretical model of ...vehicle dynamics with four degrees of freedom was derived with full consideration of lateral, transverse, lateral and longitudinal motions, and a joint simulation was carried out on MATLAB/CarSim software with steering wheel angular step input. The difference between the lateral velocity output of the model built in this paper and the output of the CarSim model is 0.005m/s at most, and the difference between the transverse swing angular velocity output and the output of the CarSim model is no more than 0.2deg/s; the difference between the lateral tilt angle output and the output of the CarSim model is no more than 0.5deg. In summary, the output of the model built in this paper matches well with the output of the CarSim model, that is to say In other words, the dynamics model developed in this paper can better reflect the vehicle driving characteristics under the vehicle angular step conditions.
This paper focuses on the stability control algorithm for four-wheel independent steering (4WIS) and four-wheel independent drive (4WID) electric vehicle (EV) with the coordinated control of ...four-wheel steering (4WS) and direct yaw-moment control (DYC) techniques. In order to design an adaptive gain-scheduled robust controller for stability control, linear parameter-varying (LPV) system and H∞ optimal control theory are applied. The polytopic model is proposed to build the LPV system for 4WIS-4WID EV. Taking structured uncertainties and sensor noise into consideration, gain-scheduled robust controller is designed and worked out using linear matrix inequality (LMI). To verify the performance of the adaptive gain-scheduled robust controller, fishhook maneuver and sinusoidal steering maneuver are carried out based on hardware-in-the-loop (HIL) tests. Test results indicate that the adaptive gain-scheduled robust controller can improve vehicle's handling stability especially in extreme conditions. Meanwhile, the designed controller shows strong robustness to suppress system parametric perturbation.
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