Transient Control Research Articles

Transient voltage stability emergency control strategy for HVDC receiving end power grid based on global orthogonal collocation

When asynchronous motors, especially double-fed asynchronous motors in large capacity pump storage are the main loads in the high voltage direct current (HVDC) receiving end power grid, the increase of the equivalent slip of asynchronous motor load may cause transient voltage instability. In order to recover the voltage rapidly in the grid, the emergency reactive power support needs to be quick and accurate. A method for transient voltage stability emergency control by temporarily reducing DC current is proposed, the inverter station is used as emergency reactive power source for the HVDC receiving end power grid. In detail, firstly, aiming at the quantitative calculation of DC current, a nonlinear optimization model with the optimization variable of DC current and the objective of minimizing energy transmission reduction of HVDC is established. Further, in order to achieve fast solution and meet the accuracy requirements, global orthogonal collocation (GOC) is incorporated into the optimization model to transform the differential equations of both objective function and constraints into algebraic equations, thus the optimization is transformed into a nonlinear programming (NLP) problem, by which the emergency control strategy, in specific, the optimal DC current control scheme is obtained. Finally, the modified IEEE 14 benchmark is used to verify the effectiveness and superiority of the proposed strategy.

Research on thermal protection of piezoelectric pressure sensor for shock wave pressure measurement in explosion field

PurposeThe purpose of this study is to clarify the mechanism of ambient and transient temperature effects on piezoelectric pressure sensors, and to propose corresponding compensation measures. The temperature of the explosion field has a significant influence on the piezoelectric sensor used to measure the shock wave pressure. For accurate shock wave pressure measurement, based on the actual piezoelectric pressure sensors used in the explosion field, the effects of ambient and transient temperatures on the sensor should be studied.Design/methodology/approachThe compensation method of the ambient temperature is discussed according to the sensor size and material. The theoretical analysis method of the transient temperature is proposed. For the transient temperature conduction problem of the sensor, the finite element simulation method of structure-temperature coupling is used to solve the temperature distribution of the sensor and the change in the contact force on the quartz crystal surface under the step and triangle temperatures. The simulation results are highly consistent with the theory.FindingsBased on the analysis results, a transient temperature control method is proposed, in which 0.5 mm thick lubricating silicone grease is applied to the sensor diaphragm, and 0.2 mm thick fiberglass cloth is wrapped around the sensor side. Simulation experiments are carried out to verify the feasibility of the control method, and the results show that the control method effectively suppresses the output of the thermal parasitic.Originality/valueThe above thermal protection methods can effectively improve the measurement accuracy of shock wave pressure and provide technical support for the evaluation of the power of explosion damage.

Enhanced transient angle stability control of isolated power grid based on phase sequence exchange

An isolated power grid (IPG) lacks the support of the external power grid, and a single generator or load accounts for a large proportion of the total capacity. Once transient angle instability, the generator and load shedding is not effectively. Phase sequence exchange (PSE) uses power electronic devices to switch the three-phase sequence, thereby reducing the power angle of the generator by 120° and preventing the system from losing stability. This paper proposed a PSE scheme for transient angle instability applied to IPG. The local measurements of IPG are used to identify the critical generator, and the system trajectory is obtained through large-step integration. The stability is assessed by the concavity of the trajectory. Once the trajectory swings from the concave area to the convex area, the IPG loses transient stability, at which point the generators in the critical cluster simultaneously PSE prevent transient instability. Based on Simulink and RTDS platform, the scheme is verified in a 39-bus 10-machine system and an existing IPG system. The results show that the proposed scheme can effectively restore the stability of the IPG, outperforming generators and load shedding.

ANALYSIS OF THE CONTROL SYSTEM OF A WIND PLANT CONNECTED TO THE AC NETWORK

The dynamics of the development of alternative power sources over the past few decades are presented, which gives reason to talk about the trends in the further development of wind energy. An analysis of the structures and technical characteristics of wind generators is provided, namely, types of electric motors, power circuits of semiconductor converters that provide the generation of electrical energy to the general industrial electrical network. The issue of the possibility of operation of wind generators in wide wind ranges, the issue of emission of reactive power and higher harmonics of currents to the general industrial electrical network, as well as the issue of the efficiency of various structures of wind generators are considered. A wind turbine control system with an asynchronous generator is proposed. A study of transient control processes and energy compatibility of a full energy conversion wind turbine with a power supply network by simulation computer modeling in the Matlab / Simulink software environment is given. The obtained result indicates the possibility of operation of an asynchronous generator with a short-circuited rotor as part of a wind turbine, which makes it possible to provide power to the alternating current network at low wind speeds.

Research on HVDC Supplementary Two-Stage Transient Control and Smooth Switching

HVDC additional transient control is an essential means to elevate the transient stability of AC/DC interconnected systems and the inevitable requirement of intelligent transmission. Two-stage transient additional control and a smooth switching strategy are proposed. By establishing an extended state observer for unbalanced power in the system disturbance, the real-time and accurate estimation of unstable power is realized, and an adaptive emergency power support controller is constructed. The mathematical model of the system is identified by using Total Least Squares-Estimation on Signal Parameters via Rotational Technique (TLS-ESPRIT). Based on the singular value reduction theory, the HVDC additional Active Disturbance Rejection Damping Controller (ADRDC) that can inhibit the low-frequency oscillation of the system is designed. Finally, two switching strategies are designed based on the change in the state of the network fault switch and the change in the power angle oscillation curve. The three-in-feed HVDC system is built in PSCAD, and the simulation analysis is carried out. The simulation results confirm the validity of the proposed method.

DC Transformers in DC Distribution Systems

With the rapid development of power electronics technology and its successful application, many demonstration projects of medium/low-voltage DC (M-LVDC) distribution systems have been constructed. The DC transformer (DCT) is the key equipment in the M-LVDC distribution system for interconnecting the MVDC and LVDC buses. In this paper, the characteristics of DCTs are summarized. The existing topologies of DCTs are analyzed, and the relevant control strategies are researched, including steady-state control, transient control, and cascaded control. The engineering application examples of DCTs are introduced by interpreting the medium and low-voltage DC distribution system demonstration project in Wujiang City, Suzhou. Finally, the challenges faced by the DCT are given, and the future development trend is predicted. This perspective provides a constructive basis for DCTs and an important reference for M-LVDC distribution systems.

Design optimization and energy performance evaluation of a dedicated outdoor air system with dual cooling sources

Dedicated outdoor air systems can save cooling energy and improve thermal comfort compared to conventional air-conditioning systems. Although many studies have investigated the energy performance of dedicated outdoor air systems for a certain application, there is a lack of a modeling resource to investigate with how the designs of the system are coordinated with control strategies aiming to improve its energy efficiency. This paper aims to optimize dedicated outdoor air system designs and develop a flexible model to evaluate the performance of the system. First, two innovative energy-saving designs of dedicated outdoor air system with dual cooling sources were proposed. Alternative design 1 optimizes the structure of the fresh air unit, while alternative design 2 builds on alternative design 1 by coupling it with a heat recovery system. Then, the two innovative systems and a baseline design were modeled using the equation-based Modelica tool. Finally, the energy performance of the three systems was evaluated under a hot and humid climate. Results showed that the Modelica-based models are able to capture the transient control strategy details. Alternative design 2 was found to be the optimal design among the three designs, with the highest energy efficiency ratio of chiller plants at 5.3. Moreover, it can reduce the cooling load supply by 9.3% and save about 7.4% on the energy consumption of chiller plants compared to the baseline design. In addition, alternative design 2 has a payback period of only 2.7 years, compared to the baseline design. It reveals the benefit of the heat recovery system in reducing the energy consumption and the cost of the cooling system. The developed dedicated outdoor air system simulation model can provide an evaluation for further improving the system optimization design, control strategy, and equipment configuration in engineering applications.

Fixed time robust control for tower cranes with unmatched disturbances and input saturation

SummaryTo address the challenging problem of fixed‐time anti‐sway and positioning control for tower cranes with uncertain disturbances and input saturation, a novel fixed‐time anti‐saturation robust algorithm is proposed. First, on the basis of a newly designed fixed‐time convergence system, a fixed‐time disturbance observer (FTDO) is developed to estimate the matched and unmatched disturbances. Then, an anti‐saturation compensator is employed to deal with the input saturation and make the control input leave the saturated region rapidly. Upon which, a novel non‐singular fast terminal sliding mode surface is presented. Furthermore, in order to ensure the stability of each subsystem, a hierarchical sliding mode surface taking into account unmatched disturbances and input saturation is designed. Finally, the FTDO based hierarchical sliding mode control law is introduced to improve the transient control performance and robustness of tower cranes. The fixed‐time convergence of the closed‐loop system is proved by Lyapunov technique. Numerical simulations for four scenarios demonstrate the validity of the presented control scheme and fastest convergence speed in comparison to the recently proposed fixed‐time control methods.

Adaptive finite-time fault-tolerant control for switched nonlinear systems with actuator fault and dead-zone via prescribed performance

In this work, an adaptive finite-time fault-tolerant control (FTC) technique for a class of switched nonlinear systems in strict-feedback form is presented. The switched nonlinear systems are considered under the influence of actuator fault, input-dead zone, and external disturbances. A prescribed performance function is used to ensure transient and steady-state control performance. To approximate unknown functions and minimize the negative effect of faults, radial basis function neural networks (RBFNNs) are used. With the help of neural networks and the backstepping method, an adaptive finite-time tracking controller is constructed. For the stability analysis of the proposed approach, the common Lyapunov function (CLF) is employed. Based on the Lyapunov function method, it has been shown that all the signals in the closed-loop system are semi-globally practically finite-time (SGPF)-stable. Also, the tracking error converges to a small residual set with the prescribed performance bounds. Finally, two simulation examples show the effectiveness of the presented control method, one of which is an application to a continuous stirred tank reactor (CSTR).

Robustly Cooperative Control of Transient Stability for Power System Considering Wind Power and Load Uncertainty by Distribution Preserving Graph Representation Learning (DPG)

Aiming at the influence of wind power and load uncertainty on the transient stability of a power system under low carbon mode, this paper first proposes a collaborative preventive and emergency control model of transient stability by distribution preserving graph representation learning (DPG). Second, the uncertainty set of wind power output and load demand is studied, and the mathematical form of the two-stage robust transient stability collaborative control model is proposed. Then, the latest artificial intelligence technology is embedded into the global optimization algorithm of the model so as to further improve the solving efficiency of the algorithm. Finally, based on the developed improved two-stage robust optimization framework, an effective collaborative control method for transient stability is developed. The transient stability prediction and control system developed in this project is not only conducive to large-scale wind power grid connection but also expected to make academic contributions to development of power system transient stability and practical simulation verification.

A Physics-Informed Action Network for Transient Stability Preventive Control

This letter proposes a physics-informed action network (PIAN) for power system transient stability preventive control (TSPC). The network firstly renders deep learning to reduce the TSPC complexity. Unlike common data-driven methods that superficially imitate control experience, TSPC is then analytically embedded into the proposed PIAN network, so that to enforce the network to learn in-depth physical patterns. The well-learned PIAN enables highly generalized real-time decisions. Comparisons with one model-based and two data-driven baselines on the IEEE 39-bus system and the IEEE 145-bus system highlight that, the proposed method enables highly reliable control decisions, and beats the others in terms of decision efficiency and generalizability.

Design-Oriented Analysis and Transient Stability Enhancement Control for a Virtual Synchronous Generator

Under fault conditions, virtual synchronous generators (VSGs) are prone to lose transient stability, similar to synchronous generators. However, the existing studies on VSG transient stability are not comprehensive. The transient characteristics of VSGs are highly affected by control parameters, but the transient models of VSGs in existing studies are overly simplified. In addition, the critical clearing angle (CCA) and critical clearing time (CCT) are two indices used to measure the transient stability of a system, but there are few studies that consider both CCA and CCT. In this article, we analyze the CCA and CCT quantitatively to describe the transient stability boundary of a VSG under different control parameters and fault conditions. Then, an equal proportional area criterion is proposed to provide guidance for the control of virtual inertia in the VSG. Based on a theoretical analysis, a transient control method for a VSG is proposed, which can improve the transient stability of the VSG in terms of both CCA and CCT. Finally, simulation and experimental tests are performed to validate the correctness of the theoretical analysis and the proposed method.

The effect of age and mitigation strategies during hot water immersion on orthostatic intolerance and thermal stress.

What is the central question of this study? The aim was to characterize adverse responses to whole-body hot water immersion and to investigate practical strategies to mitigate these effects. What is the main finding and its importance? Whole-body hot water immersion induced transient orthostatic hypotension and impaired postural control, which recovered to baseline within 10min. Hot water immersion was well tolerated by middle-aged adults, but younger adults suffered from a greater frequency and severity of dizziness. Cooling the face with a fan or not immersing the arms can mitigate some of these adverse responses in younger adults. Hot water immersion improves cardiovascular health and sporting performance, yet its adverse responses are understudied. Thirteen young and 17 middle-aged adults (n=30) were exposed to 2×30min bouts of whole-body 39°C water immersion. Young adults also completed cooling mitigation strategies in a randomized cross-over design. Orthostatic intolerance and selected physiological, perceptual, postural and cognitive responses were assessed. Orthostatic hypotension occurred in 94% of middle-aged adults and 77% of young adults. Young adults exhibited greater dizziness upon standing (young subjects, 3 out of 10 arbitrary units (AU) vs. middle-aged subjects, 2 out of 10 AU), with four terminating the protocol early owing to dizziness or discomfort. Despite middle-aged adults being largely asymptomatic, both age groups had transient impairments in postural sway after immersion (P<0.05), but no change in cognitive function (P=0.58). Middle-aged adults reported lower thermal sensation, higher thermal comfort, and higher basic affect than young adults (all P<0.01). Cooling mitigation trials had 100% completion rates, with improvements in sit-to-stand dizziness (P<0.01, arms in, 3 out of 10 AU vs. arms out, 2 out of 10 AU vs. fan, 4 out 10 AU), lower thermal sensation (P=0.04), higher thermal comfort (P<0.01) and higher basic affect (P=0.02). Middle-aged adults were predominantly asymptomatic, and cooling strategies prevented severe dizziness and thermal intolerance in younger adults.

Dual-output PID transient control of an electric-assisted air charge system

Turbo-compressor assembly (also called turbocharger) is added to diesel engines to increase their power density and improve performance. However, during power step-up operations, the added turbocharger system could lead to a significant delay of engine response (also called turbo-lag) which negatively impact drivability. In this paper, an external electric compressor (eBoost) is added to a turbocharged, large displacement diesel engine to significantly reduce turbo-lag, along with a bypass valve. Now, the air charge system has two control targets (boost (intake manifold) pressure and rate of exhaust-gas recirculation (EGR)) but with four control actuators including EGR valve, variable geometry turbo (VGT) vane position, eBoost speed and bypass valve, making it challenge for developing the associated control scheme. In this paper, a dual-output PID (proportional-integral-derivative) controller is proposed for controlling the boost pressure using the VGT and eBoost to reduce turbo-lag, and a transition logic is also devised to detect transient operating conditions to activate the eBoost, along with the closing and opening of the bypass valve, with maximum benefit. The EGR rate PID control remains unchanged. The addition of the eBoost is shown to improve transient response time by up to 55% and reduce transient NOx emissions by up to 42% during transitional operations without negatively impacting steady-state engine performance or emissions. Note that transient performance can be further improved for production implementation when a single engine control module is used by eliminating communication delay among multiple control systems.

Emerging robust and data‐driven control methods for uncertain learning systems

Emerging robust and data‐driven control methods for uncertain learning systems

Does prefrontal connectivity during task switching help or hinder children’s performance?

The ability to flexibly switch between tasks is key for goal-directed behavior and continues to improve across childhood. Children’s task switching difficulties are thought to reflect less efficient engagement of sustained and transient control processes, resulting in lower performance on blocks that intermix tasks (sustained demand) and trials that require a task switch (transient demand). Sustained and transient control processes are associated with frontoparietal regions, which develop throughout childhood and may contribute to task switching development. We examined age differences in the modulation of frontoparietal regions by sustained and transient control demands in children (8–11 years) and adults. Children showed greater performance costs than adults, especially under sustained demand, along with less upregulation of sustained and transient control activation in frontoparietal regions. Compared to adults, children showed increased connectivity between the inferior frontal junction (IFJ) and lateral prefrontal cortex (lPFC) from single to mixed blocks. For children whose sustained activation was less adult-like, increased IFJ-lPFC connectivity was associated with better performance. Children with more adult-like sustained activation showed the inverse effect. These results suggest that individual differences in task switching in later childhood at least partly depend on the recruitment of frontoparietal regions in an adult-like manner.

Numerical investigation on high-speed jet actuation for transient control of flow separation

Flow separation around a lifting body was controlled using a high-speed jet generated via impulsive actuation, and important flow features associated with the transient dynamics were numerically investigated. A jet flow was impulsively applied to the VR-12 airfoil using a boundary condition modeled as a COMPACT module in the wind tunnel experiments. A delayed detached-eddy simulation based on the Spalart–Allmaras turbulence model was conducted. Computational results indicated that the aerodynamic characteristics quickly varied in the early stage after jet initiation, and that the impact of the actuation on the flow behavior was gradually reduced through a larger time scale than the freestream convection. A detailed investigation was performed to assess relevant flow features, and two distinct flow characteristics associated with the transient dynamics were identified: reattachment and recirculation. Reattachment in the early stage after actuation yielded a high suction peak near the leading edge and rapidly enhanced the lift force. Recirculation in the later stage affected gradual variations in the aerodynamic forces and moment to the baseline flow via the generation of a low-pressure region on the suction side.

Transient stability analysis and enhancement control strategies for interconnected AC systems with VSC-Based generations

This paper analyzes the transient angle stability mechanism of interconnected AC power systems with voltage source converter (VSC) based generations and presents a stability improvement control strategy for the VSCs. Firstly, the mathematical model of the prototype AC system with both synchronous generator (SG) and VSC is developed, considering the dynamics of the pre-fault, fault-on, and post-fault systems. For the heterogenous three-machine system, the analytical method for the critical clearing time (CCT) is proposed for transient stability assessment. Then, the evolution of the transient stability margin of the AC system is studied, considering the impact of the VSCs. Under the conditions that VSCs can keep synchronism with the grid during the fault, reducing the active current of the VSCs benefits the transient angle stability of SGs. Based on the mechanism analysis, an enhancement control strategy is developed. It achieves active and reactive current modulation of the VSC using the frequency measurements of the critical SGs (CSGs) in the AC system. The proposed method devotes to boosting the electromagnetic power of CSGs during the entire transient process. Finally, time-domain simulations in PSCAD/EMTDC demonstrate the theoretical analysis. The effectiveness and robustness of the enhancement controller are further validated by the time-domain simulations in a 2-area interconnected system with 4 SGs and a modified New England 39-bus test system.

Online Classification of Transient EMG Patterns for the Control of the Wrist and Hand in a Transradial Prosthesis

Decoding human motor intentions by processing electrophysiological signals is a crucial, yet unsolved, challenge for the development of effective upper limb prostheses. Pattern recognition of continuous myoelectric (EMG) signals represents the state-of-art for multi-DoF prosthesis control. However, this approach relies on the unreliable assumption that repeatable muscular contractions produce repeatable patterns of steady-state EMGs. Here, we propose an approach for decoding wrist and hand movements by processing the signals associated with the onset of contraction (transient EMG). Specifically, we extend the concept of a transient EMG controller for the control of both wrist and hand, and tested it online. We assessed it with one transradial amputee and 15 non-amputees via the Target Achievement Control test. Non-amputees successfully completed 95% of the trials with a median completion time of 17 seconds, showing a significant learning trend ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> < 0.001). The transradial amputee completed about the 80% of the trials with a median completion time of 26 seconds. Although the performance proved comparable with earlier studies, the long completion times suggest that the current controller is not yet clinically viable. However, taken collectively, our outcomes reinforce earlier hypothesis that the transient EMG could represent a viable alternative to steady-state pattern recognition approaches.

Impact Analysis of Digital Delay on Power Factor and Compensation Strategy for Electric Traction PWM Rectifier

Due to fast dynamic response and simple implementation, the transient direct current control (TDCC) strategy is widely used for electric traction rectifiers in high-speed train drive applications. However, the inevitable digital delay may increase the steady-state error of the TDCC and consequently degrade the ac-side power factor (PF). To address this, a comprehensive effects analysis of digital delay on traction rectifier is first performed, in which the relationship between the digital delay and PF is revealed and quantified. Furthermore, a phase shift compensation scheme is proposed to improve the PF. In this scheme, the modulation signal is compensated by shifting a specified angle, where the calculation of phase shift angle only needs a few control parameters. Extensive experimental tests are carried out to verify the effectiveness of the proposed compensation method.