Double Loop Control Research Articles

A novel fault ride-through technique for grid-connected Photo Voltaic energy systems

ABSTRACTIn this article, a novel fault ride-through technique has been implanted with a double control loop method. This method is implemented with voltage-source converters, where the active and reactive power could be easily done with the voltage control loop and inherent current control loop. The proposed system has been implemented to grid-connected photovoltaic systems, and the results have been explored and compared with the existing techniques. An additional control strategy is implemented successfully for satisfactory performance of the system during low irradiance periods, and the system is made capable to provide Q-support to the grid according to the system operators request with the help of Q-set point.

Decoupled Current Control With Synchronous Frequency Damping for MMC Considering Sub-module Capacitor Voltage Ripple

Capacitor voltage ripple in the fundamental frequency is distinctive in the performance of modular multilevel converters (MMCs), unlike other voltage-source converters. First, in order to reveal the influence of capacitor voltage ripple, the coupling effect of conventional MMC double-loop control strategy is investigated to explain the unsatisfactory response. Then, decoupled current control with synchronous frequency damping is proposed, eliminating the coupling terms in the presented average value MMC model, which can improve the system dynamic behavior. Moreover, the damping index is defined and designed in the proposed control strategy to compromise between current decoupling and oscillation damping. Furthermore, the dynamic MMC characteristics with the decoupled current control and appropriate damping index are explored with detailed theoretical analysis. Finally, the simulation results validate the effectiveness of the proposed control strategy.

Dynamic Switching of Two Degree-of-Freedom Control for Belt-Driven Servomechanism

This paper proposes a new two degree-of-freedom control structure such that the robustness control of a belt-driven servomechanism is adequately addressed. In conventional design approaches, a trade-off between robust stability and robust tracking performance is unavoidable because the control engineer must take different frequency regions into consideration. In this paper, a frequency-dependent switching control structure is proposed, where the feedback connection to the external-loop controller is dynamically switched between the outputs of the controlled plant and its nominal model. The disturbance attenuation at lower frequencies by the double-loop control, as well as the robust stability at higher frequencies through the reference feedforward control, can be achieved at one fixed two degree-of-freedom control structure. The feasibility of the proposed approach is verified by theoretical analysis and experimental results.

Design of backstepping controller for PV-wind hybrid system with grid-interfacing and shunt active filtering functionality

This paper presents the design of a double loop controller for the grid interconnection of PV–wind hybrid system with shunt active filtering and neutral current compensation capabilities. Using Lypunov stability theory-based procedure, a backstepping controller is designed for the outer loop DC link voltage control. The adaptive nature of back stepping controller results in better dynamic performance compared to conventional controllers. Inner loop consists of instantaneous power theory-based controller for harmonic current compensation. Instantaneous power theory is modified by employing positive sinusoidal sequence regulator and self-tuning filter to improve the system performance in unbalanced and distorted grid voltage conditions. A dynamic model of the system is considered for the design. Numerical simulations are done in MATLAB/Simulink platform for different system conditions to verify the effectiveness of controller in grid interfacing of renewable sources, and the shunt active filtering.

Design of backstepping controller for PV-wind hybrid system with grid-interfacing and shunt active filtering functionality

This paper presents the design of a double loop controller for the grid interconnection of PV–wind hybrid system with shunt active filtering and neutral current compensation capabilities. Using Lypunov stability theory-based procedure, a backstepping controller is designed for the outer loop DC link voltage control. The adaptive nature of back stepping controller results in better dynamic performance compared to conventional controllers. Inner loop consists of instantaneous power theory-based controller for harmonic current compensation. Instantaneous power theory is modified by employing positive sinusoidal sequence regulator and self-tuning filter to improve the system performance in unbalanced and distorted grid voltage conditions. A dynamic model of the system is considered for the design. Numerical simulations are done in MATLAB/Simulink platform for different system conditions to verify the effectiveness of controller in grid interfacing of renewable sources, and the shunt active filtering.

Monte-Carlo Based Optimal Control Strategy Through State Estimator in Autonomous Space Systems

The present research relies on a control strategy to deal with the dynamics and its kinematics of the space systems, while a band of parameters uncertainties and disturbances in line with the variations of the thrust vector, center of mass, engine misalignment, moments of inertial and so on are taken into real consideration. To present the investigated outcomes in such a real situation, the process noise that are related to a set of thrusters and the measurement noise that are also related to a set of sensors are considered to be dealt with through optimal state estimator scheme. There are the double control loops including the inner loop and the outer loop, which are organized based upon a combination of low and high thrusts levels to handle three-axis rotational angles and its rates. The aforementioned thrusts levels in connection with the uncertainties and disturbances are handled through the Monte-Carlo based method to consider the proposed approach performance in a series of experiments. The acquired investigated results indicate that the performance of the proposed strategy is verified in which the well-known state-dependent Riccati equation based on the three-axis rotational angles and the corresponding angular rates is considered as the benchmark approach to be compared in the same conditions. DOI: http://dx.doi.org/10.5755/j01.itc.46.4.15391

Problems of Group Pursuit of a Target in a Perturbed Environment

In this paper, we consider some game-theory problems of group pursuit of a target under perturbations. Here, the players are unmanned flight vehicles (FVs) whose mathematical models are given by transfer functions that describe a double-loop control system with an autopilot and certain settings to provide the necessary stability of flight. According to the separation principle, without loss of generality, solutions are considered in a pitch plane. In the case of an antagonistic game, the velocity of the target is higher than that of the pursuers. The problem is solved when one of the pursuers gets close enough to the target or when the target manages to evade the pursuers. The target tracking problem implies that a randomly-arranged FV group approaches the target and flights near it during a specified time period. The low-velocity target seeks to evade the pursuers as far as possible. Finally, in the path following problem, each FV needs to fly along the trajectory given by the motion of a corresponding reference target. In the process of problem solving, each FV implements a set of heuristic behavioral strategies in a perturbed environment by following the rules of pitch angle and velocity selection. In the experimental part of this paper, some situations typical for these problems are modeled.

Research on Short Circuit Current Characteristics of Doubly-fed Wind Power Generator Considering Converter Regulation

When fault occurs in the grid, the short circuit characteristics of doubly-fed induction generator (DFIG) are more complicated due to the coupling influence of generator electromagnetic transient and converter regulation. In view of this problem, a DFIG stator/rotor short circuit current calculation method considering the transient regulation of both rotor-side and grid-side converters is proposed in this paper. First, DFIG fault equivalent network considering the rotor-side converter control is established, and the analytical expressions of stator/rotor currents in this network are derived. On this basis, considering the DC bus voltage fluctuation, the double-loop transient control process of the gird converter in the short circuit process is described quantitatively. Thus, the mechanism of the second harmonic in the stator short circuit current is revealed, and the expression of the harmonic component is derived. Finally, the analytical expressions of stator and rotor short circuit full currents are obtained. Simulation results verify the correctness and feasibility of the proposed method.

Double-loop PI controller design of the DC-DC boost converter with a proposed approach for calculation of the controller parameters

Parameters of digital proportional–integral/proportional–integral–derivative controllers are usually calculated using commonly known conventional methods or solution of discrete-time equations. In literature, a model-based compact form formulation for calculation of discrete-time proportional–integral/proportional–integral–derivative controller parameters has not been come across yet. The proposed model-based compact form formulations are introduced to calculate the proportional–integral parameters in discrete time as a new approach. Generally, different types of control techniques are chosen in similar studies for double-loop control for direct current–direct current boost converter control except proportional–integral/proportional–integral. In this study, double-loop proportional–integral controller is used as a different control method from literature. By this way, the most important advantages of the proposed study are to reduce different design methods to a unique proportional–integral design method and shorten all calculations. The accuracy of the double-loop proportional–integral controller’s parameters calculated using the model-based compact form formulations is validated both in simulation and experimental studies under various disturbance effects. Satisfactory performance of the proposed controller under model uncertainty and other cases are comparatively shown with the predefined performance criteria.

Adaptive Nonsingular Fast Terminal Sliding Mode Control for Braking Systems with Electro-Mechanical Actuators Based on Radial Basis Function

In this paper an adaptive non-singular fast terminal sliding mode (NFTSM) control scheme is proposed to control the electro-mechanical actuator (EMA) in an electric braking system which is a complex electro-mechanical system. In order to realize high-performance brake pressure servo control, a radial basis function (RBF) neural network method is adopted to deal with the difficulty of estimating the upper bound of the compound disturbance in the system, to reduce the conservatism of the design of sliding mode switching gain, and effectively eliminate sliding mode chattering. The simulation results show that, compared with a linear controller, the proposed control strategy is able to improve the servo performance and control precision. In addition the response speed of the braking actuator is enhanced significantly, without changing the traditional double-loop control structure.

Power control of 5-phase PMSG-diode rectifier-interleaved Boost set under health and fault modes

This paper deals with a fault tolerant marine energy conversion chain. The proposed structure minimizes active components and increases the phase number of generator. Hence, power control of 5-phase Permanent Magnet Synchronous Generator-diode rectifier set associated to 3-interleaved Boost converter is investigated. Dynamic small-signal models of Boost chopper are established. The control strategy is based on double loop control scheme: an inner control loop for DC current and an outer one for output power. The inner loop is guaranteed by an excellent analog current controller. Performances of this power control strategy are highlighted in both health and fault modes. The effects or disturbances caused by load variations or faults are well rejected.

Double Loop Control Design for Boost Converters Based on Frequency Response Data

This paper presents a data driven approach for PI control design based on frequency response data and calculations of stabilizing sets. The geometrical interpretation of the loci of stability margins allows to determine the parameters of a PI controller from a space of achievable specifications, constructed from frequency response data. As illustration for the use of the proposed approach in engineering applications, regulation of the output voltage of a boost power converter circuit under a double loop control strategy is presented. Numerically, it was possible to generate enough amount of data to perform accurate predictions. The key to apply the proposed approach with success was the generation of a Bode diagram for the system with fine resolution, avoiding the explicit necessity for mathematical models.

Integrated control of direct yaw moment control and active suspension system for 4wd vehicles

This paper presents an integrated control of DYC (direct yaw moment control system) and ASS (active suspension system) for 4WD (four-wheel drive) vehicles. In order to improve the comprehensive performance of 4WD vehicles, a ten degree of freedom nonlinear vehicle dynamics model is established and the torque distribution characteristic of an inter-wheel torque distribution device is analyzed. Based on the two degree of freedom linear vehicle model, the direct yaw moment controller with distribution of driving force is designed by means of sliding mode variable structure control. The active suspension system controller with a double-loop control structure is designed on the basis of its dynamics model. According to the analysis of the influence of the suspension on the vehicle steering performance, the integrated control of direct yaw moment control system and active suspension system is studied. The simulation of step steering condition and single lane change condition of vehicle is carried out using MATLAB/Simulink software. The simulation results show that the integrated control system can obviously improve vehicle riding comfort and handling stability much more than the individual control.DOI: http://dx.doi.org/10.5755/j01.mech.23.3.18481

Stabilization and analytical tuning rule of double-loop control scheme for unstable dead-time process

The presence of unstable dead-time systems in process plants often leads to a daunting challenge in the design of standard PID controllers, which are not only intended to provide close-loop stability but also to give good performance-robustness overall. In this paper, we conduct stability analysis on a double-loop control scheme based on the Routh-Hurwitz stability criteria. We propose to use this unstable double-loop control scheme which employs two P/PID controllers to control first-order or second-order unstable dead-time processes typically found in process industries. Based on the Routh-Hurwitz stability necessary and sufficient criteria, we establish several stability regions which enclose within them the P/PID parameter values that guarantee close-loop stability of the double-loop control scheme. A systematic tuning rule is developed for the purpose of obtaining the optimal P/PID parameter values within the established regions. The effectiveness of the proposed tuning rule is demonstrated using several numerical examples and the result are compared with some well-established tuning methods reported in the literature.

A parameter identification model for the Photovoltaic grid-connected inverter

The estimation of the photovoltaic (PV) inverter model parameters could lay the foundation for analyzing the grid-connected operation of PV generation system. In this paper, the control parameters to be identified are determined first through the analysis of the double loop control system structure of the PV inverter. The concerned parameters includes four proportional and integral coefficients (kPU, kIU, kPI and kII) and the filtering inductance (L). Then a parameter identification model based on simulated annealing-particle swarm optimization (SAPSO) algorithm is proposed to identify the control parameters in MATLAB environment. The comparison between the identification results of the SAPSO and the other optimization algorithms indicates that SAPSO identification model possesses high accuracy and fast convergence speed. The simulation results with identified values under the disturbance of temperature and irradiance demonstrate that SAPSO identification model has a strong generalization ability.

Adaptive super-twisting sliding mode control for a three-phase single-stage grid-connected differential boost inverter based photovoltaic system

This paper presents an adaptive super-twisting sliding mode control (STC) along with double-loop control for voltage tracking performance of three-phase differential boost inverter and DC-link capacitor voltage regulation in grid-connected PV system. The effectiveness of the proposed control strategies are demonstrated under realistic scenarios such as variations in solar insolation, load power demand, grid voltage, and transition from grid-connected to standalone mode etc. Additional supplementary power quality control functions such as harmonic compensation, and reactive power management are also investigated with the proposed control strategy. The results are compared with conventional proportional-integral controller, and PWM sliding mode controller. The system performance is evaluated in simulation and in real-time.

Double‐loop control strategy for SRGs

In this study, a novel double-loop control strategy is proposed to improve performance of switched reluctance generator (SRG) systems. The proposed double-loop control contains a power loop to control output power and an efficiency loop to optimise system efficiency. Development of the double-loop control contains three parts. First, a modified angle–voltage control (MAVC) scheme is developed to control phase current over the entire operating range. Second, firing parameters are optimised to enlarge the output power range when the SRG is controlled by MAVC. The turn-off angle is calculated by a simplified model; the turn-on angle and the DC-link voltage are optimised by differential evaluation algorithm. Third, an online mechanical power estimator is designed, with which the input mechanical power can be estimated for online efficiency optimisation in the efficiency loop. In the end, simulation and experimental results are presented to validate resulting improvements of the proposed control strategy.

T-S Fuzzy Model Based H-Infinity Control for 7-DoF Automobile Electrohydraulic Active Suspension System

This paper presents a double loop controller for a 7-DoF automobile electrohydraulic active suspension via T-S fuzzy modelling technique. The outer loop controller employs a modified H-infinity feedback control based on a T-S fuzzy model to provide the actuation force needed to ensure better riding comfort and handling stability. The resulting optimizing problem is transformed into a linear matrix inequalities solution issue associated with stability analysis, suspension stroke limit, and force constraints. Integrating these via parallel distributed compensation method, the feedback gains are derived to render the suspension performance dependent on the perturbation size and improve the efficiency of active suspensions. Adaptive Robust Control (ARC) is then adopted in the inner loop design to deal with uncertain nonlinearities and improve tracking accuracy. The validity of improvements attained from this controller is demonstrated by comparing with conventional Backstepping control and a passive suspension on a 7-DoF simulation example. It is shown that the T-S fuzzy model based controller can achieve favourable suspension performance and energy conservation under both mild and malevolent road inputs.

微电网逆变器的改进型下垂控制策略

本文通过对传统下垂控制算法的有功、无功分析，引入虚拟电感的电压电流双环控制策略，虚拟电感使逆变器等效输出阻抗成感性，从而通过调节感抗匹配程度提供功率均衡效果；提出一种多逆变器并联运行的改进型下垂控制算法，通过改进型下垂控制参数设置，减弱了阻抗对环流的影响。实验仿真结果表明，改进型多逆变器并联的微电网改进型下垂控制算法提高了多逆变器的并联运行性能，有效减小了多逆变器并联运行的环流问题，大大提高了多逆变器并联运行的无功均衡效果。 In this paper, through the analysis of active and reactive power of traditional droop control algorithm, the voltage and current double loop control strategy is introduced. The virtual inductor causes the equivalent output impedance of the inverter into emotional, to provide a power equalization effect by adjusting the impedance matching degree; an improved droop control algorithm is proposed for multi-inverter parallel operation, and the influence of impedance on the circulation is weakened by the droop control parameters setting. The simulation results show that the improved droop control algorithm of multi-inverters parallel operation in micro-grid improves the performance of multi-inverters parallel operation. The circulating current problem of multi-inverters parallel operation is effectively reduced, and the reactive power balance effect of multi inverters parallel operation is greatly improved.

Droop control strategy of the AC/DC hybrid micro‐grid based on quasi‐PR control

With the developments of renewable energies and integrations of new loads into distribution system, the hybrid of AC and DC has been becoming the typical existing form of the micro-grid. Studying on the droop control strategy will be very important for improving the safe and economic operation of micro-grid. Therefore, this study aims at thoroughly analysing a novel droop control strategy of the hybrid AC/DC micro-grid. First of all, the analysis model of the hybrid AC/DC micro-grid is built by connecting the traditional AC and DC micro-grid. Next, the typical droop control strategy of AC and DC micro-grid is introduced, respectively. Then, the voltage outer loop of quasi-proportional resonance (PR) control strategy and its optimal parameters are presented based on the analysis of the voltage–current double-loop control strategy. Finally, the simulation model of AC/DC micro-grid in Matlab/Simulink is utilised to compare the performances of the Proportional Integral (PI) and quasi-PR droop control strategies. The results show that the proposed quasi-PR has better performances in control accuracy and harmonic suppression.