Piecewise Control Strategy Research Articles

Effect of piecewise damping torques and coefficients on power absorption of a point-absorber wave energy converter

Wave energy converters (WECs), especially point-absorber WECs, are of great interest in recent years due to the global energy crisis. The power take-off (PTO) control strategy plays a crucial role in the motion response and power absorption of the WEC. This study investigates a WEC on a multi-float power generation platform as a case study, and compares four different control strategies. These control strategies are classified into two types based on the method of generating PTO damping: Type-A, which applies damping torque, and Type-B, which applies damping coefficient. Furthermore, each type has two subtypes: continuous and piecewise, depending on whether the damping torque or coefficient is continuous in the upward and downward motions of the WEC. The results indicate that the Type-B control strategy improves the power quality compared with the Type-A control strategy. Among the subtypes, the piecewise control strategy achieves greater power absorption than the continuous control strategy, while keeping the motion performance at an acceptable level.

Hybrid-Type Dual Active Bridge DC–DC Converter for Ultrawide Input-Voltage Range

This paper proposes a hybrid-type dual active bridge (H-DAB) topology and extended gain control (EG) method applied to the ultra-wide input-voltage range. The H-DAB is obtained by adding an auxiliary half-bridge to the conventional current-fed dual active bridge (CF-DAB) topology. The auxiliary half-bridge can assist the CF-DAB to achieve ZVS on the one hand, and further expand the voltage gain range on the other. The proposed extended gain control (EG) expands the input voltage range of ZVS for all switches by calculating the optimal intermediate bus voltage. In addition, the backflow power has also been drastically reduced. The proposed piecewise control strategy simplifies the complexity of control. The proposed topology and the control method are verified by the experimental results of a 500 W prototype. The input voltage range is 27 – 240 V and the output voltage is 375 V. The experimental results proved that the proposed scheme achieves ZVS of all switches in a wide input voltage range and power range, and the efficiency is improved.

Event-based distributed resilient control strategy for microgrids subject to disturbances and hybrid attacks

As a typical class of Cyber-Physical Systems (CPSs), microgrids (MGs) are susceptible to malicious cyber attacks and disturbances that can compromise their security and reliability. To address this issue, an event-triggered distributed resilient control method is proposed in this paper to mitigate the impacts of disturbances, FDI and DoS attacks on MGs. The proposed approach employs a piecewise control strategy and utilizes adaptive method to achieve the secondary control objective of MGs. In order to conserve computing and communication resources, an event-triggered mechanism is adopted and its parameter selection is associated with attacks. This design ensures system stability while also eliminating Zeno behavior. By applying Lyapunov stability theory, it can be proven that the algorithm proposed in this paper is capable of achieving the desired control objective. Finally, the effectiveness and superiority of the developed method are demonstrated through simulation examples.

Supercritical CO2 mixture Brayton cycle with floating critical points for concentrating solar power application: Concept and thermodynamic analysis

A novel concept of supercritical Brayton cycle with floating critical points is proposed to cope with the rapid deterioration of cycle performance at high heat sink temperatures. By coupling the power cycle with a distillation based composition tuning subsystem, the circulating mixture composition in the cycle can be altered dynamically to obtain the desired critical points at various ambient temperatures, thereby leading to a better match between the cold-end parameters of power cycle and the heat sink conditions. A thermodynamic model is established for the proposed novel system based on a recompression layout with single stage reheating. Four binary mixtures, including CO2–H2S, CO2–Butane, CO2–Isobutane, and CO2–Butene are employed. Simulation results indicate that an increasingly larger improvement in cycle efficiency compared to the pure CO2 cycle can be obtained as the ambient temperature increases from 20 to 50 °C. When the composition tuning process is not considered, the CO2–H2S cycle shows the best performance among the four mixture cycles, with an improvement between 1.3% and 7.4% being achieved over the entire temperature range. Several feasible schemes for composition tuning subsystem are proposed and compared in terms of energy consumption. Finally, the hourly efficiencies of the integrated system are evaluated based on typical daily weather conditions, with a piecewise control strategy for critical points. It is found that although the use of CO2–H2S causes relatively high energy consumption for distillation, a significant improvement in the daily average thermal efficiency of the integrated system can still be achieved, with efficiency being increased by 3.5%-5.1% in comparison with pure CO2 cycle on hotter days.

Hybrid simulation model for navigation performance evaluation of the Three Gorges–Gezhouba Dams under novel regulations

As an important project on the golden waterway of the Yangtze River in China, the Three Gorges–Gezhouba Dams (TGGD) plays a pivotal role in the construction of the Yangtze River Economic Belt. To improve the efficiency and safety of ship traffic, some novel navigation regulations have been implemented that change the TGGD operation obviously. For example, a piecewise control strategy proposed in the regulations is applied to control the traffic flow of ships under a sectional manner. With the implementation of these regulations, how to understand the dynamic effects of new changes on TGGD has been an important problem. The purpose of this work is to evaluate the navigation performance of the TGGD via a data- and event-driven hybrid simulation model developed by multi-agent and discrete-event modeling theories. The model simulates the three significant navigable scenarios inherent in the actual operating environment: dry season, wet season, and flood season, reflecting the real situations. The input data come from the statistical analysis of the actual navigation data provided by the Three Gorges Navigation Administration. The validity and reliability of the model are verified by comparing the output results with actual data. Moreover, a set of test experiments are designed to explore the TGGD navigation limit and analyze the key factors that restrict the navigation capacity of the TGGD system. The work is expected to provide a certain decision support for the future cooperative scheduling optimization of the TGGD.

Finite-Time Fuzzy Bounded Control for Semilinear PDE Systems With Quantized Measurements and Markov Jump Actuator Failures.

This article presents a novel reliable fuzzy output feedback controller for a class of semilinear parabolic partial differential equation systems with Markov jump actuator failures. First, the control strategy's novelties include the following aspects: 1) the considered system is represented by using a fuzzy modeling approach, based on which a new asynchronous fuzzy observer is constructed via utilizing a series of discrete output signals that are induced by samplers and quantizers; 2) a novel Markov jump input model, which is more fit for real applications, is introduced to depict various stochastically occurring actuator faults; and 3) inspired by the above discussion, a reliable mode-dependent fuzzy piecewise control strategy, which only needs limited actuators, is developed. Then, some new conditions, which can ensure that the closed-loop system is finite-time bounded, are established. Furthermore, some slave matrices are introduced to relax the strict constraints caused by asynchronous membership functions. Finally, two simulation examples are provided to support the validity of the proposed method.

Active Control Method Based on Equivalent Stiffness and Damping Coefficient for an Electromagnetic Isolation System

For improving the performance of an electromagnetic isolation system with reasonable parameters and avoid the parameter tuning problem of a PID controller, an active control method is put forward based on equivalent stiffness and damping coefficient. In this paper, the range of equivalent stiffness coefficient and damping coefficient of the electromagnetic force are calculated based on the required range of dynamic performance indexes. According to the nonlinear expression between electromagnetic force and coil current and gap, the relationships between the coil current and equivalent stiffness coefficient and damping coefficient are established. Then, the equivalent stiffness coefficient and damping coefficient can be satisfied by the controlled current in different gaps for meeting the required dynamic performance indexes. For reducing the maximum overshoot and the number of oscillations of the system, the active control method with the piecewise equivalent stiffness and damping coefficient is proposed based on the piecewise control strategy to realize the variable control parameters of the isolation system. Simulation and experimental results verify that the control method based on the equivalent stiffness and damping coefficient can obtain the desired dynamic performance indexes and the proposed control method with the piecewise strategy can not only reduce the setting time of the system, but also ensure the stability of the system.

Piecewise control strategy for electric spring

Electric spring (ES) as a device to solve the voltage fluctuation problem caused by the connection of a large number of renewable energy sources to the power grid has developed quickly. ES which involves a power inverter with a capacitor in DC side (ES-C) with the simple structure and low cost has great potential for application with strict control requirements and some operation details are not been discussed. In this study, based on the analytical solution of ES-C's operating points, the operation region of ES-C is divided into four parts. Also, a piecewise control strategy was proposed to ensure the safe and stable operation of ES-C. With the piecewise control, ES-C can participate in system frequency regulation while maintaining load voltage as rated voltage. Also, the simulations in PSCAD/EMTDC proved that the proposed piecewise control can switch between operation regions and can make full use of the operating points of ES-C.

A Piecewise Control Strategy for a Bidirectional Series Resonant Converter

An energy storage system (ESS) plays an important part in a renewable energy generation system for stable and efficient power harvesting. To realize the function of an ESS, a bidirectional DC/DC converter with high power density and high efficiency is highly desired. In this paper, a high-frequency (HF) isolated dual-bridge series resonant converter (DBSRC) with a piecewise control strategy is proposed for an application with a wide variation of voltage gain. The proposed control strategy is based on dual-phase-shift modulation for a balance between complexity and flexibility. With this proposed control strategy, zero-voltage switching is kept for all switches on the low-voltage side and half of switches on the high-voltage side. Besides, there is no circulation energy on the low-voltage high-current side for full load operation. A step-by-step design procedure is also included to calculate the converter components and control parameters. Verification of the analysis and design are performed successfully through simulation and n experimental test. Comparisons with some existing control methods are also made experimentally, which highlights that the proposed control strategy is able to achieve comparable performance as the reported optimal current control with simpler calculation and implementation.

Cascade compound controller for direct-drive gear shift modules in automated mechanical transmission

A direct-drive gear shift module, which is based on electromagnetic linear actuator (EMLA), is introduced to improve the performance of the shift-by-wire system in automated mechanical transmission. The research background and approaches are first proposed. Then, the structure, characteristics and dynamic model of the EMLA are presented. In order to improve the shift quality, the position and force modes of the EMLA are divided to realize piecewise control strategy for the gear shift process. A cascade two degree of freedom compound controller is designed for these two modes. Specifically, the feedforward controller is based on the differential flatness to achieve high-response tracking performance and the feedback controller is based on the linear extended state observer to ensure robustness against plant uncertainties and disturbances. Simulation and experiment results proved that this cascade compound controller is effective, the duration of the whole shifting process is minimized, and the shift quality is significantly improved. The direct-drive gear shift module is technically feasible.

Research of Control Strategy in the Large Electric Cylinder Position Servo System

An ideal positioning response is very difficult to realize in the large electric cylinder system that is applied in missile launcher because of the presence of many nonlinear factors such as load disturbance, parameter variations, lost motion, and friction. This paper presents a piecewise control strategy based on the optimized positioning principle. The combined application of position interpolation method and modified incremental PID with dead band is proposed and applied into control system. The experimental result confirms that this combined control strategy is not only simple to be applied into high accuracy real-time control system but also significantly improves dynamic response, steady accuracy, and anti-interference performance, which has very important significance to improve the smooth control of the large electric cylinder.

GRAPHICS-BASED CONTROL DESIGNS FOR NONMINIMUM-PHASE NONLINEAR SYSTEMS SUBJECT TO INPUT AND OUTPUT CONSTRAINTS

ABSTRACT This article deals with the output regulation of nonminimum-phase systems subject to input and output constraints. Through the off-line static data reconciliation algorithm for a class of stable nonlinear bioreactors, the static feedforward control can ensure constant disturbance attenuation in spite of input multiplicities and actuators constraints. Under the pseudo-steady-state error diagnoses and a graphics-based mechanism for disturbance estimation, the proposed error feedback control scheme will induce the piecewise output regulation. Based on the “intelligent” algorithm for tuning improvement, the closed-loop simulation shows that the piecewise control strategy turns out to be robust against the unknown disturbances.

Nonlinear Behaviour And Control Of Active Electromagnetic Bearings

This paper investigates nonlinear behaviour and control of magnetic actuators used in electromagnetic bearings,via a high-speed rotor supported by ten electromagnetic actuators and subjected to imbalance and external forces. The actuators having forces proportional to the square of the electric control current and inversely proportional to the square of distance from shaft surface are controlled using a simple and feasible control strategy. The piece-wise control strategy used here has made the system adaptive to changes in both inputs and internal system parameters at the same time as the required energy is kept to a minimum. Fewer computational steps are required with this control strategy, and the use of an online digital computer results in higher shaft speeds and a better response to larger high-frequency disturbances. Finally, the authors show that the measurement of centrifugal forces and accelerations is not necessary to control the system, and that the bearing system can adapt to these forces.

Learning piecewise control strategies in a modular neural network architecture

The authors describe a multinetwork, or modular, neural network architecture that learns to perform control tasks using a piecewise control strategy. The architecture's networks compete to learn the training patterns. As a result, a plant's parameter space is adaptively partitioned into a number of regions, and a different network learns a control law in each region. This learning process is described in a probabilistic framework and learning algorithms that perform gradient ascent in a log-likelihood function are discussed. Simulations show that the modular architecture's performance is superior to that of a single network on a multipayload robot motion control task. >