Multi-loop Control Structure Research Articles

A modified perturb and observe MPPT algorithm with zero steady state oscillation for single-phase grid-connected transformerless solar inverter

ABSTRACT This paper proposes a modified perturb and observe (P&O) algorithm to improve the performance of maximum power point tracking in a grid-connected solar inverter. The proposed method eliminates the steady state oscillations in photovoltaic panel voltage under stable irradiance conditions there by enhancing its performance. It also retains the simplicity of conventional P&O algorithm and introduces only one additional step of checking the quantum of power change to bypass the perturbations. A cascaded multi-loop control structure is adopted to achieve the objectives and retain the ability to respond to changing environmental conditions. The proposed and conventional P&O algorithms along with a designed 1 kW single-phase grid-connected transformerless solar inverter are simulated in PSIM to perform a comparative study. Furthermore, the proposed algorithm is validated experimentally on the developed solar inverter prototype.

Vibrations control of railway vehicles using decentralized proportional integral derivative controller with flow direction optimization algorithm

The reduction of vibration-induced discomfort in vehicles is an important goal in the field of transportation engineering. Several mathematical models with various controlling techniques, from classical to modern, have been employed to achieve better ride comfort. Still, no comprehensive solution has yet been found. Therefore, this paper proposes a 17-degree-of-freedom (minimum number of coordinates) dynamic model of a full-scale railway vehicle integrated with wheel-rail contact forces and an active suspension system. Two controllers, termed system and force tracking controllers, suppress the vehicle body's vibrations. Based on a multi-loop control structure, three optimally tuned Proportional Integral Derivative controllers evaluate the desired control forces and performs the system controller’s action. While the force-tracking controller generates the command voltage to track that forces. The parameters of controllers are tuned with a novel metaheuristic optimization algorithm known as the flow direction algorithm (FDA), and the results are compared with two other optimization techniques, i.e., particle swarm optimization and ant colony optimization. The simulated results show that the ride comfort of the vehicle is improved with FDA, as the root mean square values of the lateral, roll, and yaw accelerations are reduced by 42.01%, 33.12%, and 48.24%, respectively. Moreover, the simulated results of the proposed model are validated with the experimental results of accelerations. The simulated results show that the proposed system tuned with the metaheuristic algorithm outperforms with a significant reduction in vehicle vibrations.

Design of a Multiloop Control Structure for Load-Disturbance Attenuation and Power-Mismatch Mitigation in Isolated Multiport Power Converters

This article proposes a multiloop control structure for isolated multiport power converters (IMPCs), which includes a multiloop load-disturbance attenuation controller (MLDAC) and also an improved multiloop power-mismatch mitigation controller (MPMMC). The inherent capability of the IMPC to use a common magnetic link (CML) instead of multiple magnetic links offers an attractive solution to design a compact multimodule-based IMPC. With the proposed MLDAC, the IMPC can regulate the system voltage for any load disturbance without requiring any feedforward output current sensor. Moreover, the proposed MPMMC effectively mitigates leakage parameter mismatch and strictly balances the power routing in the multiple ports of the IMPC. The proposed MLDAC and MPMMC are decoupled with an improved decoupling mechanism. Additionally, this article develops a control law to indicate a safe operating area of the MPMMC. The strict voltage regulation of the IMPC under random load disturbance facilitates plug-n-play connectivity and supply of power to pulsed power loads. Moreover, eliminating the power-mismatch issues in the CML ensures equal thermal stresses and duty-life cycles of the solid-state switching devices. The performance of the proposed MLDAC is tested and compared with existing disturbance attenuation techniques. The simulation and the experimental results substantiate the superiority of the proposed MLDAC and MPMMC.

Optimization and model-based control of sustainable ethyl-methyl carbonate and diethyl carbonate synthesis through reactive distillation

As excellent solvents of lithum-ion electrolyte, ethyl-methyl carbonate (EMC) and diethyl carbonate (DEC) are synthesized through transesterification of dimethly carbonate (DMC) and ethanol. Process intensification, optimization and the corresponding control scheme of the synthesized process are essential when sustainability is becoming a necessity. In the present work, the intensified flowsheet for EMC and DEC production process was firstly proposed and optimized with conventional reactive distillation (RD) and reactive dividing wall column (RDWC), respectively. Compared with RD process, RDWC could achieve 25.3% and 8.2% total annualized cost reduction for EMC and DEC production process, respectively. And carbon dioxide emission could be decreased by 29.4% and 11.7% by further integrating RD and separation column into RDWC arrangement for DEC and EMC production. Then multi-loop PI control schemes were developed as benchmark and linear model predictive controller was designed to handle the persistent feed disturbance. The superiorities of model-based controllers for the strongly interactive and coupled system are demonstrated by the dynamic response comparisons in terms of settling time, overshoot and integral of squared error (ISE), especially for the controlled variables with poor control performance under conventional multi-loop PI control structure. To summarize, the comprehensive control performance index-ISE with MPC is reduced by 55.9%–99.1%, as compared to those under PI control strategy.

Finite Horizon Nonlinear Suboptimal Control for an Autonomous Soaring UAV

In this paper, a suboptimal nonlinear discrete control for nonlinear discrete affine systems is implemented in an autonomous soaring unmanned aerial vehicle (UAV) to improve energy consumption and performance. General expressions for this controller are obtained from the continuous nonlinear guidance model of a fixed-wing UAV and applied in a multiloop control structure. Simulation results in the task of trajectory tracking inside a thermal updraft and a comparative study with a proportional derivative (PD) controller validated the effectiveness of this method.

Control of single-phase photovoltaic H6 inverter in grid-connected and stand-alone modes of operation

This paper proposes a control strategy for single-phase transformerless photovoltaic H6 inverter with capability of operation in both grid connected and stand-alone modes. This control strategy enables seamless transition between two modes without any reconfiguration of control structure and need of any external communication. A multi-loop control structure including an inner voltage and current control with PR controller and outer power control with droop controller is utilised to make the inverter operate in both modes. In grid-connected mode, the power control loop regulates reference voltage and frequency for voltage control loop, to adjust power flow of inverter to the main grid while in islanded mode, reference voltage and frequency are determined according to droop characteristic of inverter to supply local load demand. The simulation and experimental result are used to verify the performance of the proposed control.

Practical Challenges in Real-Time Demand Response

We report on a real-time demand response experiment with 100 controllable devices. The experiment reveals several key challenges in the deployment of a real-time demand response program, including time delays, uncertainties, characterization errors, multiple timescales, and nonlinearity, which have been largely ignored in previous studies. To resolve these practical issues, we develop and implement a two-level multi-loop control structure integrating feed-forward proportional-integral controllers and optimization solvers in closed loops, which eliminates steady-state errors and improves the dynamical performance of the overall building response. The proposed methods are validated by Hardware-in-the-Loop (HiL) tests.

A NARX Model Reference Adaptive Control Scheme: Improved Disturbance Rejection Fractional-Order PID Control of an Experimental Magnetic Levitation System

Real control systems require robust control performance to deal with unpredictable and altering operating conditions of real-world systems. Improvement of disturbance rejection control performance should be considered as one of the essential control objectives in practical control system design tasks. This study presents a multi-loop Model Reference Adaptive Control (MRAC) scheme that leverages a nonlinear autoregressive neural network with external inputs (NARX) model in as the reference model. Authors observed that the performance of multi-loop MRAC-fractional-order proportional integral derivative (FOPID) control with MIT rule largely depends on the capability of the reference model to represent leading closed-loop dynamics of the experimental ML system. As such, the NARX model is used to represent disturbance-free dynamical behavior of PID control loop. It is remarkable that the obtained reference model is independent of the tuning of other control loops in the control system. The multi-loop MRAC-FOPID control structure detects impacts of disturbance incidents on control performance of the closed-loop FOPID control system and adapts the response of the FOPID control system to reduce the negative effects of the additive input disturbance. This multi-loop control structure deploys two specialized control loops: an inner loop, which is the closed-loop FOPID control system for stability and set-point control, and an outer loop, which involves a NARX reference model and an MIT rule to increase the adaptation ability of the system. Thus, the two-loop MRAC structure allows improvement of disturbance rejection performance without deteriorating precise set-point control and stability characteristics of the FOPID control loop. This is an important benefit of this control structure. To demonstrate disturbance rejection performance improvements of the proposed multi-loop MRAC-FOPID control with NARX model, an experimental study is conducted for disturbance rejection control of magnetic levitation test setup in the laboratory. Simulation and experimental results indicate an improvement of disturbance rejection performance.

An internal model control design method for failure-tolerant control with multiple objectives

The selection of control structure is a critical step in the design of a control system since it can largely affect the achievable control performance. This paper presents a general internal model control (IMC) structure with multiple degrees-of-freedom for the design of control systems with multiple objectives (i.e., reference tracking and load and output disturbance rejection), so that controllers are designed independently of each other. The optimal performance of controllers is shown to remain intact when a controller is taken off-line, for example, due to actuator and/or sensor failures. This feature circumvents the need to redesign the remaining on-line controllers for optimal failure-tolerant control. The proposed control approach is used to derive IMC control structures for multi-loop cascade and coordinated control systems. The performance of the control approach is demonstrated on a simulated thin-film drying process in continuous pharmaceutical manufacturing for several multi-loop control structures and a variety of control-loop component failures.

Parallel Control Method of Microgrid Inverter Based on Adaptive Droop Control

Energy is the driving force of social and economic development. With the gradual depletion of conventional energy and the increasingly prominent ecological and environmental problems, the power industry needs to find a sustainable development path. Parallel control of microgrid inverters based on adaptive droop control is an important part of future intelligent and sustainable power systems. However, with the continuous increase of power generation equipment capacity and the continuous increase of load power consumption, the form of power supply by a single inverter can no longer meet the requirements. Therefore, parallel connection of multiple inverters has been widely used in the microgrid. In this paper, a set of parallel control methods for microgrid inverters based on adaptive droop control is established. This paper is based on the inductance of the inverter’s terminal impedance, and the amplitude of the inverter terminal voltage is positively correlated with the output reactive power and has a strong correlation It is concluded that the microgrid based on adaptive droop control has the ability to automatically adjust the voltage and frequency of the microgrid. Properly reducing the droop coefficient can improve the primary frequency modulation capability of the microgrid. In this paper, an improved resistive control equation is used in a parallel system, a multi-loop control structure with a quasi-resonant controller is used for the inverter in the parallel system, and a virtual complex impedance is added to perform small signal analysis on the improved resistive control equation The overall performance of the parallel system is analyzed, and the effect of different control coefficients on the system performance is clarified. The experimental research results show that when analyzing the effect of the inductance coefficient value on the equivalent output impedance in the virtual complex impedance, the value of KL is 1 At this time, the equivalent output impedance becomes resistive again, and the property is stronger than when KL is 0.05.

Структура автоматизованої системи управління інформаційною стійкістю наземної оглядової радіолокаційної станції в умовах активних завад

Надано інформаційний опис структури системи управління для пошуку і реалізації на різних рівнях та етапах управління закону управління інформаційною стійкістю режимів зондування РЛС при загрозах і впливах активних завад прикриття і самоприкриття, який узагальнює результати комплексного аналізу впливу на її побудову ряду системо утворюючих чинників. При цьому реалізується повна функція ситуаційного управління із застосуванням різних форм управління для когнітивного пошуку обґрунтованого і оперативного управлінського рішення з урахуванням поставлених цілей і ресурсних обмежень. Вона передбачає цілеспрямоване проведення на вході і виході режимів зондування кожної проблемної області аналіз і прогноз розвитку станів і динамік складових і в цілому конфліктної ситуації, а також умов прийняття рішень. Розглянута багатоконтурна структура управління дозволяє раціонально використовувати ресурсні можливості РЛС щодо забезпечення завадозахищеності її режимів зондування проблемних областей зони огляду і компонент їх систем управління з урахуванням традиційних і нових інформаційних загроз стратегії РЕП.

Multi-Loop Model Reference Proportional Integral Derivative Controls: Design and Performance Evaluations

Due to unpredictable and fluctuating conditions in real-world control system applications, disturbance rejection is a substantial factor in robust control performance. The inherent disturbance rejection capacity of classical closed loop control systems is limited, and an increase in disturbance rejection performance of single-loop control systems affects the set-point control performance. Multi-loop control structures, which involve model reference control loops, can enhance the inherent disturbance rejection capacity of classical control loops without degrading set-point control performance; while the classical closed Proportional Integral Derivative (PID) control loop deals with stability and set-point control, the additional model reference control loop performs disturbance rejection control. This adaptive disturbance rejection, which does not influence set-point control performance, is achieved by selecting reference models as transfer functions of real control systems. This study investigates six types of multi-loop model reference (ML-MR) control structures for PID control loops and presents straightforward design schemes to enhance the disturbance rejection control performance of existing PID control loops. For this purpose, linear and non-linear ML-MR control structures are introduced, and their control performance improvements and certain inherent drawbacks of these structures are discussed. Design examples demonstrate the benefits of the ML-MR control structures for disturbance rejection performance improvement of PID control loops without severely deteriorating their set-point performance.

Determination and use of feasible operation region in flash distillation control

Flash distillation is essentially a single stage mass transfer operation. The flash distillation operation is used in this work to highlight the importance of identifying the zone where a system has an appropriate behavior. In this sense, this paper presents a discussion about the use of the feasible operation region (FOR) in the design of process control structures. For this reason, three control structures are presented. The first one is the traditional one, a PID multiloop control structure. The second structure uses the FOR graphically in order to determine a better operation point and improve the control response. Finally, the third structure uses the FOR numerically for guiding the controller using a modified control structure. The improvement of the closed loop operation of the flash using the last control structure is notorious when compared with the traditional control structure.

Input Reactive Power Controller With a Novel Active Damping Strategy for a Matrix Converter Fed Direct Torque Controlled DFIG for Wind Power Generation

The LC filter at the matrix converter (MC) input, excited by the PWM MC input current, introduces unwanted resonance oscillations in the input line current. The problem is more severe with a direct torque controlled (DTC) MC due to variable switching frequency operation. Active damping of this oscillation is preferred as it eliminates the power loss in the damping resistance. However, no such active damping strategy for a DTC-controlled MC-fed system has been reported in the literature so far. This article presents an input reactive power controller and a novel active damping strategy to improve the input filter current quality of an MC-fed doubly fed induction generator (DFIG) for variable speed constant frequency wind power generation. For the MC input reactive power control, superior performance of a multi-loop control structure over single-loop is established by experimental results. Stability analysis of the closed-loop input filter system using a small-signal model reveals that the system damping is the lowest in the sub-synchronous generating mode with unity DFIG stator power factor and can be improved by proper selection of the active damping controller parameters. Effects of these parameters on the system damping are predicted from the small-signal model and verified experimentally.

Multi-loop Model Reference Adaptive PID Control for Fault-Tolerance

This study demonstrates application of multi-loop model reference adaptive control (MRAC) structure to enhance fault tolerance performance of closed-loop PID control systems. The proposed multi-loop MRAC-PID structure can transform a conventional PID control system to an adaptive control system by combining an outer adaptation loop that employs MIT rule. This control structure can be used to improvement of fault tolerance and fault detection performance of the existing closed-loop PID control systems. One of the advantages of this structure originates from the reference input shaping technique that allows adaptive control without modifying any coefficients of the existing PID controllers. Numerical and experimental studies are presented to illustrate the application of the multi-loop MRAC-PID control structure for rotor control applications.

Multiloop current control for an inductive–capacitive–inductive‐filtered grid‐connected inverter with frequency‐adaptive capability under distorted grid environment

To eliminate the adverse effects of grid voltages such as the harmonic distortion and frequency variation, this study presents a multiloop current control scheme for an inductive-capacitive-inductive-filtered grid-connected inverter. The proposed scheme is achieved by multiloop control structure which is composed of the grid-side current control loop, capacitor voltage control loop, and inverter-side current control loop. This structure has an advantage of seamless mode transfer between the grid-connected mode and islanding mode. In addition, the proposed scheme offers a frequency adaptation capability even under distorted grid environment, providing a high quality of injected current in grid-connected mode. Whereas the conventional schemes require lots of state measurements, the proposed scheme eliminates the need of additional sensing devices by employing a discrete-time state observer. The resonant controllers are implemented in outer grid-side current controller to deal with harmonically distorted grid voltage at the 5th, 7th, 11th, and 13th orders. The proposed scheme ensures the quality of grid currents even in the presence of both the harmonic distortion and frequency change in grid voltages by using only the measurement of the grid-side currents and grid voltages. Simulation and experimental results are given to validate the usefulness of the proposed scheme.

A Disturbance Rejection Control Strategy for Droop-Controlled Inverter Based on Super-Twisting Algorithm

In distributed generation systems, multiple inverters paralleled operation is essential for the power requirement of local loads. To achieve the reasonable power distribution among the inverters, droop control is an effective method for the paralleled operation systems without the control interconnection. In general, the multi-loop control structure is usually utilized to regulate the drooped voltage across local loads. However, by using the traditional multi-loop controller, such as proportional-integral and proportional-resonant controllers, the dynamic process of load variation or mode transfer is slow, even the voltage overshoot or drop may occur. To address the above issues, a compact control structure-based super-twisting algorithm has been proposed in this paper. Benefitting from the designed sliding mode controllers, the dynamic response, the load disturbance rejection, and reference tracking performance can be improved. In addition, the robustness to parameters mismatch can also be achieved by using the proposed control method. The comparative simulation and experimental results validate the correctness and feasibility of the proposed method.

Design of a robust path tracking controller for an unmanned bicycle with guaranteed stability of roll dynamics

ABSTRACTController design for a riderless bicycle is a difficult task due to its non-holonomic constraint and its complex dynamic. The problem will be more complex, when path tracking and stabilizing the roll angle of the bicycle are considered simultaneously. This paper proposes an analytical approach to stabilize the roll angle of an unmanned bicycle, in the meanwhile a desirable path is tracked by the bicycle. These two objectives are achieved due to the existing relation between the roll angle and the steering variable of the bicycle. In this paper, a multi-loop control structure is proposed to track a predetermined path. In the inner loop, the roll angle tracks a time-varying reference signal using the back-stepping method. This reference signal is manipulated in the outer loops to track the desired path. Moreover, the robustness of the system with respect to external disturbances is guaranteed by the Lyapunov redesign method. Finally, the efficiency of the proposed method is illustrated through computer simulations.

Digital Generator Control Unit Design for a Variable Frequency Synchronous Generator in MEA

Variable frequency power generation systems have been adopted for modern aircraft power systems, thus, a new generator control unit (GCU) must be designed to regulate the output voltage and obtain high quality power supply under a wide frequency range from 360 Hz to 800 Hz. In this paper, a dual digital signal processor (DSP) structure-based GCU was proposed. Multi-loop control structure was adopted with the controller parameters varying adaptively at different working conditions to obtain better performance. Different root-mean-square (RMS) calculation algorithms have been compared and the final RMS calculation scheme was determined to realize the trade-off between accuracy and computing efficiency. Experimental results show considerable performance improvements of the generator output voltage under various operating conditions with the proposed GCU.

Lyapunov Based 3D Path Following Kinematic Controller for a Fixed Wing UAV

Path following is a basic autonomous navigation capability for UAV’s and in this paper we present a nonlinear 3D path following kinematic controller. In order to solve this problem, we use the typical multi-loop control structure in which the navigation controller directs the aircraft to the desired path, while the inner loop acts as an autopilot which stabilizes the nonlinear dynamics and tracks the command generated by the outer loop. Under the assumption that the autopilot is well tuned and the airspeed, fight-path angle, and bank angle states converge to the desired response to their commanded values, we use a kinematic model as a suitable control model for the fixed wing UAV. With the introduction of a virtual target, the proposed Lyapunov based kinematic controller for outer loop can steer the UAV asymptotically to approach the desired path. The proposed controller is validated in a 6-DoF simulation environment platform named MAV3DSim.