Original Control Strategy Research Articles

Sectorial Fuzzy Controller Plus Feedforward for the Trajectory Tracking of Robotic Arms in Joint Space

In this paper, we propose a Sectorial Fuzzy Controller (SFC) with a feedforward compensation of the robot dynamics in joint space, evaluated at the desired angular positions, velocities, and accelerations, applied to the trajectory tracking of all revolute joints robotic arms. Global uniform asymptotic stability proof applying the direct Lyapunov theorem, is introduced for this new control scheme by using a strict Lyapunov function. This strict Lyapunov function is the first one within the field of fuzzy control that is applied to the trajectory control of robotic manipulators. With this strict Lyapunov function, a sensitivity analysis was also computed for this novel control scheme. Additionally, physical and simulation experimental results are given in comparison to the original control scheme, in which this new controller is inspired: the Proportional-Derivative (PD) controller plus feedforward compensation. The experimental results yielded better performance for the new fuzzy control scheme when compared to the classical structure, in both the joint position errors for similar or smaller values of applied torques, showing the expected tolerance to parametric deviations and uncertainties that all fuzzy controllers possess.

An Improved Reactive Power Sharing Method for an Islanded Microgrid

Conventional droop control is widely used for achieving proportional power sharing in islanded microgrids. The active power sharing becomes proportional to the ratings of the inverters by applying the conventional droop control. However, reactive power sharing is not proportional because of resistive feeder impedance, unequal feeder lengths, and asymmetric load distribution in the network. In this article, an existing control strategy that has been proposed for improving reactive power sharing is enhanced by removing its dependency on communication. The required synchronization for executing the correction is generated by each inverter locally using a load change detection algorithm. This modification also makes the original control strategy immune to load changes happening during the correction process. An almost accurate reactive power sharing is achieved by applying the proposed modification even for highly resistive networks. Also, a tradeoff required in tuning the controller gain is discussed. The efficacy of the proposed modification has been validated by performing detailed simulation studies and by carrying out exhaustive experimental studies on a laboratory prototype.

Research and Analysis of Permanent Magnet Transmission System Controls on Diesel Railway Vehicles

As the energy crisis and environmental pollution continue to be a gradual threat, the energy saving of transmission systems has become the focus of railway vehicle research and design. Due to their high-power density and efficiency features, permanent magnet synchronous motors (PMSM) have been gradually applied in railway vehicles. To improve the efficiency of the transmission system of diesel railway vehicles, it is a good option to use PMSM as both a generator and traction motor to construct a full permanent magnet transmission system (FPMTS). Due to the application of the new FPMTS, some of the original control strategies for diesel railway vehicle transmission systems are no longer applicable. Therefore, it is necessary to adjust and improve the control strategies to meet the needs of FPMTS. We studied several key issues that affect the reliability and comfort of the vehicles. As such, this paper introduced the FPMTS control strategy, including the coordinated control strategy of the diesel and the traction motor, the two degrees of freedom (2DOF) decoupling current regulator, the maximum torque control of the standardized unit current, the wheel slip protection control, and the fault protection strategy. The experiment was carried out on the test platform and the test run of the diesel shunting locomotive equipped with the FPMTS. The results showed that the control strategy described in this paper met the operation characteristics of the FPMTS and that the control performance was superior. The study of FPMTS lays the foundation for the subsequent application of permanent magnet motors in high-powered diesel locomotives and high-speed diesel multi-units.

Hybrid Control Strategy for Force and Precise End Effector Positioning of a Twisted String Actuator

In this article, we propose a new control approach for the twisted string actuation system; a hybrid control scheme consisting of two nested loops, considering the motor angle and the axial force at the clamping point of the actuator as the system outputs. We show that measuring the axial force at the base of the actuator, we can effectively estimate and compensate the coupling torque between the motor and the external load. Then, compensation of the coupling torque allows formulating a linear control law to control the angular position of the actuator and, at the same time, implement an external control loop to regulate the force applied by the actuator. Simulated and experimental results validate the proposed original control scheme. Furthermore, we highlight the contributions of this article in the broader context of control of twisted string actuators.

Derivation and Analysis of a Secondary-Side LLC Resonant Converter for the High Step-Up Applications

An isolated high step-up converter, which is derived from the reverse structure of a regular <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter, is proposed in this article. The proposed converter consists of an inverter stage, a secondary-side resonant tank, and an active voltage-doubler rectifier. An additional input diode is introduced into the regular push–pull inverter so as to make the magnetizing inductance free from being always clamped by the input voltage and make up new voltage gain features. The leakage inductance, which always shows a significant value when reflected to the secondary side in a high step-up transformer, can be used to make up the resonant tank. Under a simple pulse-frequency-modulation control with 0.5 duty ratios for both the primary-side and secondary-side switches, a high step-up function can be easily realized by the converter with good load regulation ability. Meanwhile, synchronous rectification (SR) can be naturally achieved by the secondary-side switches. The additional input diode can be replaced by a MOSFET with an analog SR chip to further improve the efficiency, without changing the original control scheme. The validity of the study is confirmed by a 500-W prototype with 36–42 V input and 380-V output. The peak efficiency can reach 96.9%.

Research on Voltage Control of Multi Terminal Flexible Medium Voltage DC Distribution Network

In order to solve the problem that the original control strategy cannot meet the voltage quality requirements of the system under various operation modes due to the expansion of DC distribution network scale, this paper studies the voltage control strategy of a ring type medium voltage DC distribution network. Firstly, the traditional control method is improved, the droop control is added to the margin control as the slave station control method. At the same time, the DC transformer connected with the energy storage is used as the backup voltage regulating station in case of power shortage to meet the voltage quality requirements of the system in normal operation and fault. Then, a DC voltage control strategy based on depth first search is proposed to solve the problem of voltage deviation caused by system fault, so that the distribution network can automatically adjust the control according to the real-time structure in case of fault and improve the voltage quality. Finally, the proposed control strategy is simulated in PSCAD / EMTDC to verify the effectiveness of the control strategy.

Conditioned haptic perception for 3D localization of nodules in soft tissue palpation with a variable stiffness probe.

This paper provides a solution for fast haptic information gain during soft tissue palpation using a Variable Lever Mechanism (VLM) probe. More specifically, we investigate the impact of stiffness variation of the probe to condition likelihood functions of the kinesthetic force and tactile sensors measurements during a palpation task for two sweeping directions. Using knowledge obtained from past probing trials or Finite Element (FE) simulations, we implemented this likelihood conditioning in an autonomous palpation control strategy. Based on a recursive Bayesian inferencing framework, this new control strategy adapts the sweeping direction and the stiffness of the probe to detect abnormal stiff inclusions in soft tissues. This original control strategy for compliant palpation probes shows a sub-millimeter accuracy for the 3D localization of the nodules in a soft tissue phantom as well as a 100% reliability detecting the existence of nodules in a soft phantom.

Finite-time tracking control and vibration suppression based on the concept of virtual control force for flexible two-link space robot

The dynamic modeling, finite-time trajectory tracking control and vibration suppression of a flexible two-link space robot are studied. Firstly, the dynamic model of the system is established by combining Lagrange method with assumed mode method. In order to ensure that the base attitude and the joints of space robot can reach the desired positions within a limited time, a non-singular fast terminal sliding mode (NFTSM) controller is designed, which realizes the finite-time convergence of the trajectory tracking errors. Subsequently, for the sake of suppressing the vibrations of flexible links, a hybrid trajectory based on the concept of the virtual control force is developed, which can reflect the flexible modes and the trajectory tracking errors simultaneously. By modifying the original control scheme, a NFTSM hybrid controller is proposed. The hybrid control scheme can not only realized attitude stabilization and trajectory tracking of joints in finite time, but also provide a new method of vibration suppression. The simulation results verify the effectiveness of the designed hybrid control strategy.

Autonomous Coordinated Control Strategy for Complex Process of Traffic Information Physical Fusion System Based on Big Data

In the era of big data, the global data is growing explosively. The huge growth rate makes data processing and storage difficult, especially in the field of transportation. Based on the above background, this paper aims to study the autonomous coordinated control strategy for the complex process of traffic information physical fusion system based on big data. In this paper, the information physical fusion system is applied to the modern transportation system, and it is used to realize the high integration of computation, communication and control. Realize the independent and coordinated control of the transportation system. This paper proposes an autonomous traffic management mechanism based on multi-agent CPS system. In view of the instability and untimely of the original control strategy, a new traffic optimization control strategy conflict reduction control strategy is proposed. In order to solve the complexity of traffic system, the generation method of CPS autonomous control strategy based on multi-agent is studied and analyzed. Through the evaluation and verification of the conflict reduction control strategy and the online simulation of the incremental data synchronization strategy, it can be seen that the inconsistency ratio curves of message quantity and byte transmission quantity are always kept at a relatively low level, 1% and 2%, respectively. During the whole experiment, the average number of inconsistent messages and byte transmission of the agent are ideally controlled at 1.2 messages / train and 0.5kb/train.

An Output Ripple-Free Fast Charger for Electric Vehicles Based on Grid-Tied Modular Three-Phase Interleaved Converters

An off-board dc fast battery charger for electric vehicles (EVs) with an original control strategy aimed to provide ripple-free output current in the typical EV batteries voltage range is presented in this article. The proposed configuration is based on modular three-phase interleaved converters and supplied by the low-voltage ac grid. The ac/dc interleaved three-phase active rectifier is composed of three standard two-level three-phase converter modules with a possibility to slightly adjust the dc-link voltage level in order to null the output current ripple. A modular interleaved dc/dc converter, formed by the same three-phase converter modules connected in parallel, is used as an interface between the dc link and the battery. The use of low-cost, standard and industry-recognized three-phase power modules for high-power fast EV charging stations enables the reduction of capital and maintenance costs of the charging facilities. The effect of coupling on the individual input/output inductors and total input/output current ripples has been investigated as well, considering both possible coupling implementations, i.e., inverse and direct coupling. Numerical simulations are reported to confirm the feasibility and the effectiveness of the whole EV fast charging configuration, including the proposed control strategy aimed to null the ripple of the output current. Experimental results are provided by a reduced scale prototype of the output stage to verify the ripple-free output current operation capability.

Fuzzy Logic Optimization of Composite Brake Control Strategy for Load-Isolated Electric Bus

To improve the energy recovery rate and increase the driving range of load-isolated electric buses, a composite brake control strategy based on fuzzy logic optimization is proposed. Considering the influence of the battery SOC value and the braking intensity on the braking ratio, a fuzzy controller is designed for small and medium braking strengths to optimize the control strategy. The vehicle simulation model of the load-isolated electric bus was built with the AVL CRUISE software platform. The AVL CRUISE-Simulink cosimulation was carried out under the original control strategy and the optimized control strategy. The simulation results show that, under the premise of ensuring the stability of braking, the driving range of the vehicle with the optimized control strategy is increased by 7.74% and the energy recovery rate is increased by 11.05%.

Feedback linearization-based satellite attitude control with a life-support device without communications

This paper develops a control strategy for a life-support device to be attached to an orbiting satellite to extend its operational life. The objective is met in such a way that the original satellite keeps operating without communications between the two systems (also valuable for energy efficiency). The case in which the original satellite is equipped with a feedback-linearization based controller is considered and the control law for the life-support is developed with the same methodology, obtaining a compensating control which recovers the performance of the original control strategy. Simulations validate the approach considering a real case study in various scenarios.

The Optimized Energy Saving of a Refrigerating Chamber

This paper proposes a control strategy for the energy saving of refrigerating chambers. Combining binary coding and proteome reorganization, the binary proteome algorithm (BPA) is proposed to solve this problem. The refrigeration system model is firstly established based on the performance data of compressors and temperature measurements of each refrigerating chamber. The objective function is an averaged coefficient of performance (COP), which considers the switching loss of the compressors, power consumption of the compressors, and refrigerating capacity of the chambers. The control strategy is defined as an optimization problem with constraints to avoid the ineffective operation of a refrigeration system for improving the COP. BPA is adopted to solve the control strategy for optimizing energy saving. The effectiveness and efficiency of the BPA are demonstrated using a real system, and the results are compared with the original control strategy. Results show that the average power consumption drops from 115.92 kW to 108.82 kW, and the average COP value rises from 1.92 to 2.03. The proposed control strategy is feasible, robust, and more effective in energy-saving problems. Other than energy saving, the proposed control strategy also has the benefits of reducing the evaporator frost formation, which allows the products to avoid chill damage.

Control Strategy for PHEB Based on Actual Driving Cycle with Driving Style Characteristic

To exert fully the energy economy performance of plug-in hybrid electric buses (PHEBs) and enhance the adaptability to different drivers and driving cycles, a control strategy for PHEB based on actual driving cycle with driving style characteristic is proposed in this paper. Through the actual city bus driving data, collected in real time, 6 actual driving cycles with driving style characteristic are fitted by using Principal Component Analysis (PCA) and Cluster Analysis (CA). Based on the 6 driving cycles, the key parameters of rule-based control strategy are optimized and established by a combinatorial optimization algorithm in Isight. Then, an identification model to recognize the current condition based on the Learning Vector Quantization (LVQ) neural network has been built and trained offline, which is integrated in the control strategy for PHEB to invoke the corresponding optimized key control parameters in real time. A hardware-in-the-loop (HIL) test is conducted, and the result shows that the proposed strategy could improve the energy consumption by 4.94%, compared with the original rule-based control strategy, and its validity and practicability are fully verified.

A New Control Strategy of 5-Phase PM Motor under Open-Circuited Phase Based on High Order Sliding Mode and Current References Real-Time Generation

The high quality of electrical power in high power and high reliability applications is a crucial necessity even under fault mode function. However, in these conditions, the quality of the torque is a key feature. To overcome this problem, the multiphase permanent magnet (PM) motors seems to be a very attractive choice. In order to highlight the robustness and reliability of this technology, this paper investigates the control of a five-phase PM motor under an open circuited phase fault conditions. Moreover, a High Order Sliding Mode (HOSM) controller combined to an optimal reference current generation is tested and compared to a PID controller under fault mode conditions. This original control strategy is proposed for faulted conditions. Compared to classical fault tolerant control, this strategy allows a better dynamic tracking of the non-sinusoidal reference currents and leads to a smooth torque with minimal losses even in severe fault conditions. To validate the proposed control strategy, simulation, and experimental results are presented and discussed.

Parallel Optimization of Trajectory Planning and Tracking for Three-Body Tethered Space System

This paper develops a new piecewise parallel optimal control scheme to suppress the libration of a three-body tethered system in circular orbits with a climber. Optimal control is achieved by controlling the tension in tether via regulation of tether length at the end body and the climber speed to minimize the Coriolis’ effect. Thus, the total tether length of the system is no longer constant, which is different from the classical three-body tethered system and more effective in libration suppression. To facilitate the space implementation, the original optimal control scheme is split into two parallel phases on a dual-CPU system to reduce computational burden. Phase I predicts an optimal reference state trajectory for the next time interval piecewise by an open-loop optimization with a grossly simplified three-body tethered system model. Phase II tracks the predicted reference trajectory at the current time interval simultaneously by a closed-loop receding horizon control using a full dynamic model. The simulation results reveal that the newly proposed parallel optimal control scheme is able to suppress the libration of the three-body tethered system by controlling tether tension only. Moreover, by controlling the climber's speed adaptively, the libration angles of the tethered system can be suppressed with a shorter transfer period compared with the constant climber speed.

Unified Distributed Control of Stand-Alone DC Microgrids

Stand-alone direct current (dc) microgrids may belong to different owners and adopt various control strategies. This brings great challenge to its optimal operation due to the difficulty of implementing a unified control. This paper addresses the distributed optimal control of dc microgrids, which intends to break the restriction of diversity to some extent. First, we formulate the optimal power flow problem of stand-alone dc microgrids as an exact second-order cone program and prove the uniqueness of the optimal solution. Then a dynamic solving algorithm based on primal–dual decomposition method is proposed, the convergence of which is proved theoretically as well as the optimality of its equilibrium point. It should be stressed that the algorithm can provide control commands for the three types of microgrids: 1) power control; 2) voltage control; and 3) droop control. This implies that each microgrid does not need to change its original control strategy in practice, which is less influenced by the diversity of microgrids. Moreover, the control commands for power controlled and voltage controlled microgrids satisfy generation limits and voltage limits in both transient process and steady state. Finally, a six-microgrid dc system based on the microgrid benchmark is adopted to validate the effectiveness and plug-n-play property of our designs.

Control of a point absorber wave energy converter

This paper deals with the optimization of a bottom fixed wave energy converter of heaving point absorber type (PAWEC). The PAWEC consists of a unique horizontal cylinder of radius R and length L, connected to the seabed through an extensible Power Take Off device. In this work, an original control strategy is used in order to optimize the PAWEC. The proposed method links the damping coefficient of the power take off device to the relative velocity between the buoy and the wave. This study focus on the comparison of the two cases where a passive control is adopted and where the damping coefficient is a constant. The performance of the WEC in different wave conditions for each of the two cases is investigated. The results show that the recovered energy is considerably increased owing to the adaptation of the damping coefficient with the buoy speed

A Novel MMC Sub-Module Topology With DC Fault Clearance Capability

The sub-module of the modular multilevel converter (MMC) in practical engineering mainly adopt half-bridge sub-module (HBSM), which does not have the capability to clear dc fault current. Based on the analysis of the dc fault current path of traditional HBSM, this paper proposes a novel MMC sub-module with dc fault clearance capability. It adds a bidirectional switch and two diodes to the HBSM. When the dc fault occurs, the bypass absorption circuit is introduced into the arm through the diodes and the freewheeling effect of diodes is eliminated by the sub-module capacitor voltage. Thereby, the fault current can be extinguished rapidly and the requirement for the consistency of the trigger pulse is reduced. By comparing with the operation principle of the HBSM, it can quickly block the dc fault current without changing the original control and modulation strategy. Then, the fault clearance principle of the sub-module and the voltage stress of the key power devices are analyzed. The simulation results in MATLAB/SIMLINK have verified the validity and feasibility of the proposed sub-module topology in the dc fault current clearance.

A decoupled Mechanical Shim core control strategy for a pressurized water reactor using feedforward compensation and a multimodel approach

The advanced Mechanical Shim (MSHIM) core control strategy employs two separate and independent control rod banks, namely the MSHIM control banks (M-banks) and axial offset (AO) control bank (AO-bank), for automatic reactivity/temperature and axial power distribution control respectively. The M-banks and AO-bank are controlled by two closed-loop controllers, independently, called the coolant average temperature (Tavg) controller and the AO controller. Since the motion of the M-banks and AO-bank can both affect the Tavg and AO, an interlocking design between the Tavg controller and the AO controller is adopted in the MSHIM control strategy to avoid the interference between the two controllers during power maneuvers. This design can enhance the stability of the MSHIM control system by avoiding the simultaneous movement of the M-banks and AO-bank and keeping the priority of the M-bank movement. However, the AO control performance is degraded at the same time. In the present study, a feedforward compensation decoupling method and a multimodel approach have been used to eliminate the coupling effect between the two controllers in the MSHIM control system during a wide range of power maneuvers. A multiple feedforward compensation system has been designed with integration of the feedforward compensators for the Tavg and AO controllers at five equilibrium conditions using the multimodel approach. By implementing it in the MSHIM control system, the interlocking between the M-banks and the AO-bank can be released to realize the independent and decoupling control between the Tavg and AO. The effectiveness of the decoupled MSHIM control strategy has been verified by comparing its control performance with that of the original MSHIM control strategy during typical load change transients of the AP1000 reactor. The obtained results show that superior and decoupling control of the Tavg and AO can be achieved using the proposed decoupled MSHIM control strategy.