Multi-loop Control Research Articles

A Robust Multiloop Disturbance Rejection Controller for a Doubly Fed Induction Generator-Based Wind Energy Conversion System

The doubly fed induction generator (DFIG) is a nonlinear system with various uncertainties, including parameter changes, wind speed variations, and rapid dynamic fluctuations, making model-based control techniques challenging to implement. Hence, the multi-loop active disturbance rejection controller (MADRC) is proposed as an enhanced active disturbance rejection control to stabilize and reject external disturbances and system uncertainties. In this article, two active disturbance rejection controllers (ADRCs) are connected in series to achieve the rotor side converter (RSC) controller. The performance of the proposed control strategy is first evaluated using simulation on a 3.7-kW DFIG setup, and subsequently on a 1-kW DFIG-based wind energy conversion system (WECS) developed in our laboratory. The proposed controller is compared to a proportional-integral (PI) controller, single-loop active disturbance rejection controller (SADRC), and sliding mode controller (SMC) in order to demonstrate its effectiveness. The obtained outcomes are evaluated for reference tracking, robustness to parameter fluctuation, and disturbance rejection in DFIG. External disturbances and system uncertainties are effectively mitigated by the proposed MADRC scheme.

MultiScaler: A Multi-Loop Auto-Scaling Approach for Cloud-Based Applications

Cloud computing offers a wide range of services through a pool of heterogeneous Physical Machines (PMs) hosted on cloud data centers, where each PM can host several Virtual Machines (VMs). Resource sharing among VMs comes with major benefits, but it can create technical challenges that have a detrimental effect on the performance. To ensure a specific service level requested by the cloud-based applications, there is a need for an approach to assign adequate resources to each VM. To this end, we present our novel Multi-Loop Control approach, called <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MultiScaler</small> , to allocate resources to VMs based on the Service Level Agreement (SLA) requirements and the run-time conditions. <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MultiScaler</small> is mainly composed of three different levels working closely with each other to achieve an optimal resource allocation. We propose a set of tailor-made controllers to monitor VMs and take actions accordingly to regulate contention among collocated VMs, to reallocate resources if required, and to migrate VMs from one PM to another. The evaluation in a VMware cluster have shown that the <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MultiScaler</small> approach can meet applications performance goals and guarantee the SLA by assigning the exact resources that the applications require. Compared with sophisticated baselines, <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MultiScaler</small> produces significantly better reaction to changes in workloads even under the presence of noisy neighbors.

Decentralized multi-loop auto-rolling controller for nonlinear large-scale roll-to-roll machines via velocity sensorless and tension loop adaptation approaches

Decentralized multi-loop auto-rolling controller for nonlinear large-scale roll-to-roll machines via velocity sensorless and tension loop adaptation approaches

Secure power management strategy for direct torque controlled fuel cell/ supercapacitor electric vehicles

High reliability is recommended in hybrid electric vehicle applications. In this study, a secure power management strategy has been developed for a fuel cell—supercapacitor hybrid electric vehicle. In addition to its ability to detect the occurrence of failures in vehicle power sources, the proposed power management strategy isolates the faulty source and reconfigures the control scheme to always guarantee bus voltage stability and vehicle traction even in faulty situations. The developed power management strategy enhances vehicle comfort and prevents exhausting one source over another by allowing the fuel cell and the supercapacitor to operate at different power levels. The multiloop control scheme associated with the power sources is highly reliable since both sources can run the vehicle alone and regulate the bus voltage. Vehicle speed and torque controllers are simultaneously tuned using a particle swarm optimization algorithm. Torque and speed ripples are automatically minimized via the use of a new proposed cost function. This approach made the controller design easier and gave the designer the possibility to tradeoff between the variables to be minimized.

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.

High-Performance Digital Multiloop Control of LLC Resonant Converters for EV Fast Charging With LUT-Based Feedforward and Adaptive Gain

The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter is typically adopted in battery charging applications due to its excellent performance in terms of efficiency, power density, and wide input/output voltage regulation. However, this converter is a complex high-order system characterized by a strong nonlinear behavior, featuring large variations of the small-signal gain/phase and pole location depending on the operating point. Consequently, these features pose substantial challenges in designing a closed-loop controller and providing constant dynamical performance over a wide operating range. Therefore, this article proposes a digital multiloop control strategy for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converters ensuring constant closed-loop bandwidth and excellent disturbance rejection performance across the complete converter operating region. The control scheme consists of two cascaded voltage and current loops. To design and tune these controllers, a simplified <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> dual first-order small-signal model is proposed. The system nonlinear behavior affecting the current control loop is counteracted by a real-time controller gain adaptation process, which ensures constant control bandwidth. In particular, the adaptive gain values are provided by a static switching frequency lookup table obtained experimentally. Moreover, the steady-state switching frequency value is fed forward at the output of the current loop regulator, providing a further dynamical performance enhancement. The proposed control strategy and the controller design procedure are verified both in simulation and experimentally on a 15-kW <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter prototype. The results demonstrate the superior reference tracking and disturbance rejection performance of the proposed control strategy with respect to a state-of-the-art solution based on a proportional–integral regulator.

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.

MIMO modeling and multi-loop control based on neural network for municipal solid waste incineration

The Municipal solid wastes incineration (MSWI) process with complex mechanism and strong nonlinearity is an important part of resource cycle. It is a challenge to design its multivariable controlled object model and control strategy. To solve this problem, a multi-input multi-output (MIMO) data-driven model and a multi-loop PID controller are proposed in this paper. Firstly, a feature selection method based on Pearson correlation coefficient (PCC) and expert knowledge is used to analyze the relationship between the manipulated variable and the controlled variable of MSWI process. Secondly, a MIMO Takagi–Sugeno fuzzy neural network (TSFNN) based on multi-task learning (MTL) is designed to construct the multivariable controlled object model. Thirdly, a multi-loop PID controller based on quasi-diagonal recurrent neural network (QDRNN) is constructed, which has self-feedback channel and interconnection channel, and can adjust the control parameters automatically. Next, the stability of control strategy is proved by Lyapunov second method. Finally, the modeling effect and control performance are confirmed on the simulation experiments based on the real MSWI process data.

Integrated Physical Modeling and Optimal Control Method of Limited-Angle Torque Motor in Fuel Metering Apparatus

Limited-angle torque motor (LATM) is a critical component to precisely drive the valve angle of an engine’s fuel metering apparatus and accurately measure the fuel flow, and research on it is of great significance. Thus, the LATM of a certain kind is regarded as the research object in this paper. Firstly, a Simscape-based LATM integrated physical modeling method is proposed, which can better demonstrate the real operational characteristics of a motor, compared with the current mathematical model. Secondly, a Proportional-Integral-Derivative (PID) parameter self-tuning method based on a constriction factor particle swarm optimization (CPSO) algorithm is broached since it is difficult to tune due to a large number of multi-loop cascade PID control parameters. Simulation and experimental results showed that the control performance increases by 40% in the triple closed-loop PID control system with a stronger disturbance rejection, simpler design, and quickly responds when compared with the previous empirical tuning method. The triple closed-loop PID control system comprises an angle loop + angle velocity loop + current loop and technically supports the engineering application design of motors.

Research and application of ultra-high pressure control system in strength tests

Based on the requirement of physical experiments, a ultra-high pressure control system which consisted of servo valves, a booster cylinder, and a multi-channel synchro-loading control system, was designed. A multi loop control strategy was adopted in this system, and hydraulic oil was loaded on the low-pressure side of the booster cylinder. In this way, the high precision control of low pressure increasing with high flow was attained, either was ultra-high pressure increasing, maintaining and reducing with low flow. The system was applied in a landing gear strength test successfully, the pressure control accuracy was smaller than 0.5 %, and the test task was completed satisfactorily.

Modelling and control of nonlinear negative imaginary systems

This article investigates mathematical modelling and control of a nonlinear negative imaginary system using an illustrative benchmark physical example of a quadrotor dynamic model. A generalized methodology based on Euler–Lagrange equation is applied to obtain nonlinear negative imaginary dynamic model for the quadrotor. In this method, the Kronecker product is employed to formulate the Coriolis matrix, which is then used to construct a mathematical model of a quadrotor. This article further presents nonlinear negative imaginary systems theory-based analysis and synthesis framework to find the control solution for quadrotor’s attitude stability problem while hovering. The multi-loop control scheme is applied to the quadrotor that directly uses the Euler angles (angular positions) instead of angular velocity measurements. Numerical simulation results of this paper show that the investigated control strategy ensures the asymptotic stabilization of quadrotor attitude system model in the presence of external disturbance.

SIMULATION OF CLOSED LOOP VOLTAGE CONTROL OF SEPIC CONVERTER

In this study, a robust output SEPIC DC-DC converter is designed and simulated. The studied single ended primary inductor converter (SEPIC) output voltage is regulated to a constant value regardless of its input. A double loop PI controller is designed and tuned for the voltage and current control which yields a control technique that results in simple implementation by reducing complexity. The multiloop control technique is used to improve converter behavior in case of wide system parameter variations. The controller parameters and design procedure are provided for the SEPIC converter for non zero current operation mode. The proposed implementation of the controlled SEPIC converter has been simulated in Matlab/Simulink environment. The simulations have been done with various operating conditions. Results show that the PI-controlled SEPIC rejects the disturbances and provides good tracking performance

Model-Independent Observer-Based Current Sensorless Speed Servo Systems with Adaptive Feedback Gain

This study proposes a solution to the speed control problem of servo machines in the form of multi-loop current sensorless control with a reduction in the system model dependence level and the number of feedback loops, which provides the two contributions: first, a model-independent observer estimates speed and acceleration using only the position measurement, thereby ensuring the first-order estimation error dynamics; second, the active damping acceleration stabilizes the inner loop with the adaptive feedback gain increasing and decreasing automatically according to the transient and steady-state operation modes. The experimental study highlighted the effectiveness of the acceleration loop adaptation technique, which used an actual servo system comprising the QUBE-servo2 and myRIO-1900.

Design and Analysis of Decentralized Dynamic Sliding Mode Controller for TITO Process

In this paper, a decentralized dynamic sliding mode control (DySMC) strategy is applied to a multivariable level control system. The time derivative of the control input of the DySMC is considered a new control variable for an augmented system which is composed of the original system and the integrator. This DySMC can transfer discontinuous terms to the first-order derivative of the control input and effectively reduce the chattering. The interactions between input/output variables are a common phenomenon and a challenging task in the design of multi-loop controllers for interacting multivariable processes. For reducing the interaction among variables, ideal decouplers are used. Independent diagonal controllers are designed for each decoupled subsystem, which is reduced to the first-order plus dead-time (FOPDT) model. A numerical simulation test has been carried out on a reactor system of the Industrial-Scale Polymerization (ISP). Experimental tests are performed to check the efficacy of the proposed controller using a laboratory-level coupled tank system. A comparison of the proposed approach and sliding mode controller (SMC) is presented. Simulation and experiment results show that the DySMC approach reduces the chattering, and compensates for the effect of the external disturbances, and parametric uncertainties.

Causality in Control Systems Based on Data-Driven Oscillation Identification

This paper addresses the subject of causality analysis using simulation data and data collected from a real control system. Simulated data includes Gaussian and Cauchy noise signals. Real-time series include various, mostly unknown distortions, like trends, oscillations, and noises. Presented research focuses on the oscillatory component in data and its propagation in multi-loop control systems. Oscillation identification is based on a deep decomposition process for control error time series. Identified periodic signals are used for further causality processing. The analysis uses the Transfer Entropy approach. This method belongs to the group of model-free methods. The determination of information pathways is conducted without any model or a priori process knowledge. The research investigates the impact of the oscillation time-series component on the Transfer Entropy causality analysis. The summary shows the observations obtained for given simulated datasets and those collected from real processes. The obtained results show that simulated analysis works properly. On the contrary, the direct application of the oscillation decomposition in real industrial cases may be misleading. Large datasets demand modification in the methodology. Different variants are tested. They show that oscillation propagation is biased in real systems and, therefore, the decomposition should be applied with caution. Furthermore, it is important to remember that the algorithm transition from simulated data to real industrial ones is demanding and should be done with the utmost care.

IMC-PID-FOF Multi-loop controller design for Binary Distillation Column

This paper deals with the fractional order multi-loop controller design for a distillation column. The idea is a generalization of the IMC-PID-FOF controller design method developed for monovariable systems to the distillation column model which is multivariable. The principle is based on the IMC paradigm and the choice of appropriate control configuration with minimum of interactions. The proposed method is illustrated with an example of a distillation column model taken from the literature.

Development of control strategies for an air separation unit with a divided wall column using a pressure-driven digital twin

Digital twins of process plants provide various opportunities to improve plant operation by in silico studies. A major advantage of a simulation-based digital twin is its availability prior to the physical plant. Thus, it can be used for design purposes. In this work, dynamic simulation studies of a novel air separation unit topology are conducted to develop a reliable control strategy. This novel air separation design includes an integrated argon removal column. That is, a column with the intent to remove an argon-rich fraction is included into the low-pressure column by means of a divided wall section. The liquid reflux for the integrated argon removal column is generated by an additional condenser/reboiler in the low-pressure column above the divided wall section. The intent of the argon removal is to increase the energy efficiency of large scale air separation units for oxygen production. Using the digital twin, three multi-loop PID control strategies are compared regarding reliable operability.

Dynamic High-Type Interval Type-2 Fuzzy Logic Control for Photoelectric Tracking System

This paper proposes a dynamic high-type control (DHTC) method based on an interval type-2 fuzzy logic controller (IT2FLC), which is used in the photoelectric tracking system to improve the steady-state accuracy and response speed. Adding integrators to the traditional multi-loop feedback control loop can increase the system type, thereby speeding up the response speed and improving the steady-state accuracy, but there is a risk of integral saturation. Switching the type dynamically according to the system state can avoid integral saturation while retaining the advantages of the high-type. Fuzzy logic control (FLC) can dynamically change the output value according to the input change and has the advantages of fast response speed and strong ability to handle uncertainties. Therefore, in this paper, the FLC is introduced into the high-type control system, and the output of the FLC is used as the gain of the integrator to control the on-off to achieve the goal of dynamic switching type, which is successfully verified in the experiment. IT2FLC introduces a three-dimensional membership function, which further improves the FLC’s ability to handle uncertainties. From the experimental results, compared with T1FLC, IT2FLC’s ability to handle uncertainties is significantly improved. In addition, in order to speed up the calculation speed of IT2FLC, this paper proposes an improved type-reduction algorithm, which is called weighted-trapezoidal Nie-Tan (WTNT). Compared with the traditional type-reduction algorithm, WTNT has faster calculation speed and better steady-state accuracy, and has been successfully applied to real-time control systems, which has good engineering application value. Finally, in order to reduce the interference of human factors and improve the automation level of the system, a multi-population genetic algorithm (MPGA) is used to iteratively optimize the parameters of the FLC, which improves the output accuracy. On the experimental platform of the flexible fast steering mirror (FFSM), the control effects of the traditional controller, T1FLC and IT2FLC are compared, which proves that the IT2FLC-DHTC system has a faster response performance, higher steady-state accuracy, and stronger ability to handle uncertainties.

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.

Operation and control schemes of a novel direct AC-AC modular multilevel converter

AC-DC-AC modular multilevel converter (MMC) and direct AC-AC MMC are two kinds of interfaces to integrating AC motors into power grid, and they are easily damaged from large capacitor voltage fluctuation with varying motor speed. Up to now, none of the methods could balance the reliability and power density of MMC-based motor drives system. To find a better solution to this problem, a novel direct AC-AC MMC topology is proposed in this paper. Operating principle of this topology is introduced and relative multi-loop feedback control method is designed for it. Then, simulation and experiments are conducted for verification. Compared with the traditional MMC with high-frequency injection method, the proposed topology has no common-mode voltage problem and the current stress is reduced by 38.5%. Compared with the half-bridge-based AC-DC-AC MMC, the number of capacitors and inductors of the proposed topology is reduced by 20.8% and 25%. In comparison with the direct AC-AC MMC (modular multilevel matrix converter), the number of power devices of the proposed topology is reduced by 28%. The proposed topology has higher reliability and power density.