Double Closed-loop Control Strategy Research Articles

A Robust Switching Control Strategy for Three-Phase Voltage Source Converters with Uncertain Circuit Parameters

This study proposes a novel double closed-loop robust control strategy based on a power switching affine model of three-phase voltage source converters (VSCs). The aim is to overcome the challenges posed by inaccurate mathematical models, complex controller configurations, indirect switching control, and performance degradation under circuit parameters uncertainty or load variation in conventional methods. These conventional methods rely on linearization models, duty ratio regulation, and pulse width modulation (PWM) technologies. The contributions of work are the following: (1) A two-dimensional (2D) power switching affine model is constructed without any approximation or averaging. (2) The proposed approach achieves direct switching control of three-phase VSCs, eliminating the need for complex rotation coordinate transformation, PWM, and phase locking loop (PLL), which are utilized in traditional control methods. (3) The rigor of the system stability analysis is enhanced based on the 2D power switching model compared to the existing three-dimensional (3D) current switching model. (4) A simple control structure with only two control parameters is employed to address circuit parameter uncertainties. The effectiveness and superiority of the proposed method is validated through simulation and experimental comparison results.

Accurate Stability Analysis of Three-Phase Converter System Connected to Weak Grid under Coordinate System Transformation

This paper studies the simplified impedance criterion of the three-phase converter system in different coordinate systems. In addition, the influence of small signal stability of converter units under the weak grid is discussed in three-phase converter systems. Firstly, a small signal model of a three-phase grid-connected converter system is established based on the voltage and current double closed-loop control strategy in dq real coordinate system and the dynamic characteristics of SRF-PLL (Synchronous Reference Frame Phase-Locked Loop). Then, based on the coordinate transformation, the admittance models in the dq real coordinate system and the fb complex coordinate system are derived. Through the analysis of the admittance Bode diagram, the amplitude-frequency characteristics of the three-phase converter system have conjugate symmetry in the real coordinate system and diagonal conjugate symmetry in the complex coordinate system. Therefore, the three-phase symmetrical system can be stabilized only by drawing the Nyquist curve of the open-loop transfer function GHf or GHb. The three-phase asymmetric system can also be stabilized by drawing the Nyquist curve of the modified open-loop transfer function GHfM or GHbM . Finally, the simulation results show that the converter system loses stability when the transmission line impedance Lg = 0.6 pu. In this case, the three current decoupling terms will cause the system to lose stability, but the relative stability of the current reference value is the best, and the phase angle margin is −6.8°. Also, without considering the phase-locked loop dynamics, the system is in a steady state, otherwise, the system loses stability, and the system output current has a 39 Hz oscillation, which is consistent with the theoretical analysis results.

Energy management strategy of urban rail hybrid energy storage system based on fuzzy logic system

Energy management is an important link in the effective functioning of hybrid energy storage systems (HESS) within urban rail trains. This factor significantly impacts the operational stability and economic efficiency of urban rail systems. Safety issues arise from DC bus voltage fluctuations due to varying train conditions. To address these issues, this paper proposes an energy management strategy for the urban rail HESS, which builds upon a traditional double closed-loop control strategy. This strategy incorporates a fuzzy logic system to regulate power distribution parameters and discharge thresholds dynamically. Real-time monitoring of the state of charge (SOC) of the energy storage device informs the decision-making process, utilizing a fuzzy inference system to effectively regulate power and energy distribution in response to the distinct characteristics of batteries and super-capacitors. This approach aims to mitigate power fluctuations within the traction network. To validate the effectiveness of the proposed energy management strategy, the study conducts a comprehensive simulation experiment using MATLAB/Simulink. The simulation results confirm the efficacy of the proposed strategy, highlighting its potential to enhance the stability and overall performance of urban rail train operations.

Double closed-loop feedback control strategy for enhanced external counterpulsation to regulate hemodynamic response of human common carotid artery

Enhanced external counterpulsation (EECP) is a mechanical therapy for the clinical management of ischemic cardio-cerebrovascular diseases. Applying different EECP modes to different patients would be based on the experience of physicians. Existing hemodynamic models could describe the quantitative relationship between different EECP modes and hemodynamic parameters of specific parts of human blood circulatory system. However, currently there is no closed-loop control system available for precisely, personally, and intelligently performing the EECP. Therefore, to significantly improve the clinical benefits of rehabilitation treatment of ischemic cardio-cerebrovascular diseases with the EECP, this study developed a double closed-loop physiological control algorithm for the EECP device. Firstly, a detailed lumped parameter model describing the hemodynamics of human blood circulatory system was updated based on the available models; then the EECP device was coupled to it and the updated model was tested with the clinical data; finally, a double closed-loop feedback control strategy for precise regulation of the carotid hemodynamic response by the EECP was proposed. The control objectives were to maintain the mean arterial pressure and EECP pressure amplitude of patients with two gain-scheduled proportional-integral (PI) controllers. In-silico results showed that the clinical data can prove the accuracy of the updated model, and the appropriate EECP pressure amplitude could provide patients with the best benefits. The proposed control system could generate satisfied hemodynamic effects even with noise, demonstrating its feasibility and robustness. It is also easy to apply with high accuracy, and may be the effective solutions for developing intelligent and personalized EECP devices.

Impartial Sequential Model Predictive Control of Parallel T-Type Rectifiers for Power Sharing and Circulating Current Elimination

A parallel T-type rectifier connection is often required to improve the system capacity and stability in high-power applications. However, the parallel rectifier faces the challenges of zero-sequence circulating current (ZSCC) elimination, neutral point (NP) voltage balance, DC voltage stability and power sharing. First, to solve the multi-objective optimization problem of two parallel three-level T-type rectifiers with LCL filters (LCL-3LT <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> Rs), a double closed-loop control scheme is adopted. In this scheme, an impartial sequential model predictive control (ISMPC) is proposed as the inner-loop controller for ZSCC elimination and NP voltage balance, and an adaptive droop control with voltage feedforward is designed as the outer-loop controller to achieve DC voltage stability and power sharing for each rectifier based on its capacity. Second, the main influencing factors of ZSCC in LCL-3LT <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> Rs are analyzed, and ZSCC elimination is considered as one control objective in ISMPC. Finally, ISMPC is proposed to solve the problem that sequential model predictive control (SMPC) could not select the optimal solution due to the fixed priority and the excessive process only controlled a single objective. The proposed method is tested on a prototype hardware platform of a 10-kW and a 5-kW parallel rectifier. Experiment results demonstrate the superiority of this method over existing methods under several typical scenarios.

Research on stability control strategy of adjustable pressure wall-climbing robot based on adsorption identification

In order to solve the problem that it is difficult to accurately model the complex fluid domain in the negative pressure chamber of the robot in the process of wall climbing, and thus cannot quickly and steadily adsorb, a double closed-loop control strategy based on parameter identification and particle swarm optimization is proposed in this paper to improve the speed and stability of the adsorption response of the robot in the process of wall climbing. Firstly, a vacuum negative pressure wall climbing robot with a spring pressure regulating structure is developed, and the critical conditions of the robot’s instability are solved by mechanical analysis. Then, the rigid-flexible coupling model of the whole machine was established based on mass, spring and Maxwell viscoelastic elements. The model parameters of the adsorption system were identified by vacuum adsorption test. Compared with the experimental data, the accuracy of the model was more than 80%. On this basis, PID controller is used to adjust the adsorption response speed of the robot, a double closed-loop stable adsorption control strategy is designed, and the control parameters of the adsorption system are adjusted by using the dynamic weight standard particle swarm optimization algorithm. Finally, simulation and prototype tests show that, the proposed control strategy can shorten the static and dynamic response time of the adsorption system by about 3.5 s and 1.4 s, the flow response time by about 1.15s, the maneuvering performance of the whole system is improved by about 26%, and the parameter overshoot and steady-state error are lower, which provides a theoretical reference for the stability control and engineering application of the wall-climbing robot.

Computed torque control and force analysis for mechanical leg with variable rotation axis powered by servo pneumatic muscle

It is difficult for a humanoid leg driven by two groups of antagonistic pneumatic muscles (PMs) to achieve a flexible humanoid gait, and its inherent strong coupling nonlinear characteristics make it hard to achieve good tracking performance in a large range of motion. Therefore, a four-bar linkage bionic knee joint structure with a variable axis and a double closed-loop servo position control strategy based on computed torque control are designed to improve anthropomorphic characteristics and the dynamic performance of the bionic mechanical leg powered by servo pneumatic muscle (SPM). Firstly, the relationship between the joint torque, the initial jump angle and the bounce height of the mechanical leg is established, and then we design a double-joint PM bionic mechanical leg containing a four-bar linkage mechanism of the knee joint. Secondly, a cascade position control strategy is developed, which consists of the outer position loop and the inner contraction force loop, and the mapping relationship is designed between joint torque and antagonistic PM contraction force. Finally, we further project bounce action timing of mechanical leg to realize the periodic jumping movement of the mechanical leg, and simulation and physical experiments of the real-style machine platform have been provided to demonstrate the effectiveness of the designed SPM controller.

Study on Active Disturbance Rejection Control of Permanent Magnet Synchronous Motor Based on Variable Structure Extended State Observer

Linear extended state observer (linear extended state observer, LESO) is the core component of linear active disturbance rejection control (linear active disturbance rejection control, LADRC), and its performance is critical to the control effect. The linear ADRC is applied to the speed loop of the permanent magnet synchronous motor control system with a double closed-loop control strategy. By adding a scale factor to the linear extended state observer, the utilization efficiency of the observed signal and the observation speed is improved. On this basis, a hybrid switching strategy is adopted to achieve a smooth transition between the traditional ESO and the improved ESO, avoiding the motor speed imbalance and motor chattering caused by direct switching. Finally, the improved ADRC strategy and the traditional ADRC strategy are compared and analyzed through simulation, which verifies the effectiveness and superiority of the improved strategy.

Decoupled adaptive terminal sliding mode control strategy for a 6-DOF electro-hydraulic suspension test rig with RBF coupling force compensator

Aiming at the problems of poor tracking accuracy, low convergence speed, weak robustness of a 6-DOF electro-hydraulic suspension test system under system uncertainties and external disturbance, this article proposes double closed-loop control scheme. In the outer loop controller, this article designs a new decoupled adaptive fast nonsingular terminal sliding mode (DAFNTSM) control to achieve fast convergence rate, high accurate and adaptive disturbances estimation during trajectory tracking. Additionally, a coupling force compensator based on RBF neural network is employed, which can reduce online calculation quantity and guarantee accuracy. For six inner loop controllers, each hydraulic actuator can precisely follow the required force solved by outer loop controller. The hard-in-loop experiment results reveal that the control approach we proposed in this paper realize superior trajectory tracking characteristics in comparison with the conventional nonsingular terminal sliding mode (CNTSM) method.

Dynamic analysis and vibration control for overhead hoist transport

The OHT system is a transport device used for intra- or inter-plant transport in a fab or other factory, the load-bearing part of the goods stored under the trolley generates longitudinal vibration and lateral oscillation due to inertia force When the OHT in the air starts or stops. Firstly, the trolley dynamic model under the action of lateral thrust and longitudinal tensile force need to be established. secondly, the coupling analysis of horizontal oscillation and longitudinal oscillation on the model is carried out. Thirdly, aiming at the lateral swing and longitudinal vibration of the carriage, a double closed-loop vibration control strategy with tension control as inner loop and speed control as outer loop and carry out the simulation analysis of longitudinal vibration control is proposed. In the experiment of the ground trolley, the control strategy is applied. The simulation and experimental results show that the control method can quickly restrain the longitudinal vibration of the trolley bearing plate, reduce the pulling force of the trolley on the lifting steel belt, and avoid the large displacement of the bearing plate in the air.

Discrete-time adaptive predictive sliding mode trajectory tracking control for dynamic positioning ship with input magnitude and rate saturations

This paper investigates the discrete-time adaptive predictive sliding mode trajectory tracking control problem based on a reference sliding mode trajectory for the dynamic positioning ship with model uncertainty, environmental disturbances and input magnitude and rate saturations. Initially, a two-step delay discrete-time disturbance observer is designed to estimate the model uncertainty and environmental disturbances, and the input constraints are processed by quadratic programming. Then, an adaptive expected heading is proposed to ensure faster trajectory tracking and more stable heading changes simultaneously. Furthermore, using a double closed-loop control strategy, a new discrete-time virtual velocity controller is designed in the outer loop based on Euler discretization to convert trajectory tracking into velocity tracking. In the inner loop, a discrete-time adaptive predictive sliding mode velocity controller is designed based on a new adaptive reference sliding mode trajectory and an integral terminal sliding mode surface with disturbance estimation error. The proposed strategy can adaptively adjust the sliding mode bandwidth and convergence speed, which not only ensures the system’s rapid convergence but also reduces the tracking error and weakens the chattering. Finally, the stability analysis proves that the closed-loop system is uniformly bounded stable. Comparative simulation results verify the effectiveness of the proposed control scheme.

Research on VDG Control Strategy in Hybrid Energy Storage System of Photovoltaic DC Microgrid

With the access to many energy storage devices in the Photovoltaic DC microgrid, energy storage converters are also widely used, which have the characteristic of low inertia. Therefore, there are problems of low inertia in the optical storage DC microgrid system, which contains an energy storage converter, and the instability of the system causes by the fluctuation of micro-source and load mutation. In order to solve the existing problems, the paper proposes a Virtual DC Generator (VDG) control strategy based on the traditional double closed-loop control strategy in the hybrid energy storage system (HESS) of a photovoltaic DC microgrid. Applying this proposed control strategy can make the inertia and damping characteristics introduced into the converters, which provides sufficient inertia support for the optical storage DC microgrid and further improves the voltage quality. The microgrid system is modeled and analyzed based on VDG. The results show that the VDG control strategy effectively reduces power fluctuation of the hybrid energy storage and improves the stability of the microgrid system.

Research on Bidirectional Isolated Charging System Based on Resonant Converter

This paper proposes a two-stage bidirectional isolated charging system, which can realize the bidirectional flow of electric energy, not only making the electric energy flow from the grid side to the battery side but also converting the battery’s energy into single-phase alternating current to supply other electric equipment. The charging system also has the function of power factor correction and wide-range voltage output. The front stage of the charging system is a bidirectional totem pole structure power factor correction converter with a voltage and current double closed-loop control strategy to ensure the stability of the DC bus voltage, and the rear stage is a bidirectional CLLLC resonant converter, which adopts a high-frequency soft start strategy to reduce the inrush current during start-up and ensure the safe operation of the converter. Moreover, the frequency control strategy is used to make it have a wide range of DC output characteristics. In this paper, the principle analysis and parameter calculation of the charging system is carried out, the simulation platform and hardware circuit design are built, and a test prototype is piloted to verify the bidirectional operating characteristics of the charging system. The simulation and experimental results demonstrate the correctness of the theoretical analysis and topology design.

Control Design for the NPC Three-Level Grid-Connected Converter with Non-Ideal Grid System

Background: The large-scale distributed new energy integrations bring about various non-ideal grid situations, which could deteriorate the control performance of grid-connected converters. Objective: This study aims to improve the control performance of the grid-connected converters when the grid is non-ideal. Methods: Firstly, a neutral point clamped (NPC) three-level grid-connected converter was studied, and the characteristics of the non-ideal grid were analyzed in detail. Then, a real-time signal extraction method called generalized sliding discrete Fourier transform (GSDFT) has been proposed to extract the non-ideal signals, e.g., harmonic components and negative sequence components, based on which a double closed-loop control strategy was designed to improve the control performance of the grid-connected converters when the grid is non-ideal. Results: The experimental results show that the converter double closed-loop control strategy in the non-ideal grid environment is suitable for a variety of non-ideal grid environments, and the gridconnected effect is good. Conclusion: Firstly, this paper analyzes the characteristics of non-ideal grid and establishes the mathematical model of NPC three-level grid-connected converter in non-ideal grid environment. Secondly, aiming at the problem of characteristic harmonics and negative sequence components in non-ideal power grid, a real-time and fast extraction method of non-ideal signals based on generalized sliding discrete Fourier transform is proposed. Finally, taking the three-phase grid current of grid-connected converter as the control target, the closed-loop control strategy of non-ideal signal extraction based on GSDFT is designed, and a good control effect is achieved.

A novel design and control method for improved LCL filter three-level inverter to suppress common mode resonant current and leakage current

The method of connecting the common point of the LCL filter capacitor of the three-level grid-connected inverter to the midpoint of the DC side can effectively suppress the leakage current between the DC side photovoltaic panel and the power grid. However, the improved MLCL inverter is easy to generate common mode resonance, which results in excessively increasing the midline current and affecting the efficiency and stability of the system. Aiming at the common mode resonance problem of MLCL three-level inverter, this paper expounds the generation of common mode resonance current and large neutral current by establishing the mathematical model of the improved MLCL filter. After analyzing the restraining effect and limitation of traditional passive damping control scheme on common mode resonance, a novel filtering structure is proposed in this paper, which is combined with PI+ PR double closed-loop control scheme to solve the above problems. Simulation results verify the validity of the analysis on common mode resonance and neutral current, and the effectiveness of the scheme in suppressing common mode resonance current, midline current and leakage current is also confirmed.

Observer-Based Double Closed-Loop Control for Mixed Vehicle Groups: A Macro and Micro Perspective

The paper aims to ensure that traffic parameters are simultaneously available between sparse sensors, and to improve the traffic efficiency of expressways and achieve the consistent driving state of mixed vehicle groups. Firstly, we propose a dynamic mixed segmental linear (DMSL) traffic model with external disturbances including automated vehicles (AVs) and connected automated vehicles (CAVs) as the composition of mixed vehicle groups on the expressway. Secondly, an observer-based double closed-loop control strategy is investigated by jointly controlling the on-ramp flow in the outer-loop control system and the driving state of mixed vehicle groups on the main section of the expressway in the inner-loop control system. Thirdly, the convergence and stability of the inner-loop control system and the outer-loop control system are analyzed by using Lyapunov stability theory, and the control gain and observation gain of the double closed-loop are obtained via adopting linear matrix inequality (LMI) method. Finally, numerical simulation experiments are executed to confirm the feasibility and accuracy of the proposed control algorithm. The results illustrate that the proposed control method is effective while the percentage of automated vehicles (AVs) is gradually increasing.

Investigation of an Output Voltage Harmonic Suppression Strategy of a Power Quality Control Device for the High-End Manufacturing Industry.

Due to the influence of nonlinear loads, power quality control devices under the traditional double closed-loop control strategy suffer from a large output voltage harmonic distortion rate and a slow harmonic suppression response and cannot meet the high-quality power supply requirements of high-end manufacturing. A compound control strategy based on voltage feedback and current feed-forward is proposed to solve the voltage quality problem under a nonlinear load. Firstly, based on the mathematical model of power quality control device, the working principle and voltage current coupling relationship are analyzed. Then, an output voltage compound control strategy based on feed-forward and feedback is proposed, and the harmonic suppression mechanisms are deduced and analyzed. Finally, simulation and experimental results are presented to show that, compared with the traditional double closed-loop control strategy, the harmonic suppression effect of the composite control strategy proposed in this paper can be increased by 2.2%, and the response time is decreased to 100 ms.

Bivariate active power control of energy storage hydraulic wind turbine

With the increasing proportion of wind turbines in power system, high-precision control of power generation directly affects the proportion of wind turbines connected to the grid. This paper takes the energy storage hydraulic wind turbines (ESHWTs) as the research object, the mathematical model of the hydraulic main transmission system and the hydraulic energy storage subsystem are established, and the energy transmission and control mechanism is obtained. The corresponding relationship between the output power of the hydraulic main drive system and the hydraulic energy storage subsystem and the variable motor speed is analyzed, based on the small signal linearization method, and the power transmission state is obtained with the variable motor speed fluctuation, and a double closed-loop power control strategy is proposed under the motor speed fluctuation, with the power control requirements after grid connection, Based on MATLAB software and 24 kW semi-physical simulation test platform of energy storage hydraulic wind turbine, the output power is accurately controlled and the power output problem is solved under the fluctuation of motor speed with the proposed control strategy.

An Electromagnetic Var Compensator Suitable for Wind Power Access and Its Control Strategy

As the proportion of large-scale wind farms and distributed wind power connected to the power grid increases annually, the effects of their intermittent and random characteristics on the active and reactive power fluctuations of the power grid are becoming increasingly evident, causing frequent voltage fluctuations at the grid-connected point. To solve these problems, this study proposes a new topology of an electromagnetic var compensator (EVC) based on a rotary phase-shifting transformer (RPST). The EVC can work under capacitive and inductive conditions to compensate for inductive and capacitive power, respectively. In accordance with the parallel steady-state mathematical model of the EVC, a double closed-loop control strategy with high precision and considerable robustness is proposed for the EVC on the basis of instantaneous reactive power theory. Finally, simulations show that the topology of the proposed EVC exhibits bidirectional and continuous adjustment capability that can meet the reactive power compensation requirements of power systems with a high percentage of wind power. Compared with the existing reactive power compensation device, the EVC exhibits the advantages of high voltage, large capacity, low cost, strong impact resistance, and good tolerance, imbuing it with great prospects for development.

Error allocation model and coordination control for stringer–skin T-shape structure welding robot with multiple manipulators

A new kind of 18 degrees of freedom gantry robot with multiple manipulators could be used to complete the double-sided laser beam welding of stringer–skin T-shape structure for aircraft skin. The coordination control combined with error allocation model analysis is proposed to improve the stability and accuracy of the robot in this article. Firstly, the error model of the stringer–skin T-shape structure welding robot end effectors is analyzed. The score of the robot end effectors position error caused by each joint is obtained. Secondly, according to the path-points transformation matrix of the local coordinate system relative to the base coordinate system, the desired position of stringer–skin T-shape structure welding robot end effectors is calculated to be the input of the control model aiming at the dual-beam laser welding process. Then, the double closed-loop control strategy is proposed for stringer–skin T-shape structure welding robot coordinated motion on the basis of the end error analysis results and proportional-integralderivative (PID) method. Finally, ADAMS and MATLAB are used to establish a co-simulation platform to verify the effectiveness of the proposed coordination control strategy.