Multi-loop Feedback Control Research Articles

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.

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.

The Frequency-Domain Fusion Virtual Multi-Loop Feedback Control System with Measured Disturbance Feedforward Method in Telescopes

In the optical telescope, the stable precision of the optical path is affected by the structural vibrations. The image sensor with time delay and the micro electro-mechanical system (MEMS) accelerometer with massive drift limit the disturbance suppression performance of the closed loops. The current control methods cannot reject sufficiently vibrations due to the deficiency of the sensors, causality, and stability restrictions. In this study, the frequency-domain fusion virtual multi-loop feedback control system with measured disturbance feedforward method is proposed to suppress more structural vibrations. In spite of the deficiency of the sensors, we propose the frequency-domain fusion virtual gyroscopes (VGYR) to measure extra velocity of the system. The VGYR is estimated from the MEMS accelerometer with drift and corrected by the image sensor, and it replaces the fiber-optical gyroscopes (FOG) on the fast-stable platform because the weight of FOG is not negligible. To suppress more vibrations, the VGYR and the replaced FOG are utilized to build the virtual multi-loop feedback control system with measured disturbance feedforward, because it is not limited by the causality and stability restrictions. Therefore, the proposed method with causal ideal compensator can effectively improve stable precision and suppress much more structural vibrations in the wider frequency range. Detailed comparative experimental results adequately illustrate the advantages and effectiveness of this method.

Virtual velocity loop based on MEMS accelerometers for optical stabilization control system

In the optical stabilization control system (OSCS) control system based on a charge-coupled device (CCD), stabilization performance of the line-of-sight is severely limited by the mechanical resonance and the low sampling rate of the CCD. An approach to improve the stabilization performance of the OSCS control system with load restriction based on three loops, including an acceleration loop, a virtual velocity loop, and a position loop, by using MEMS accelerometers and a CCD is proposed. The velocity signal is obtained by accelerators instead of gyro sensors. Its advantages are low power, low cost, small size, and wide measuring range. A detailed analysis is provided to show how to design the virtual velocity loop and correct virtual velocity loop drift. Experimental results show that the proposed multiloop feedback control method with virtual velocity loop in which the disturbance suppression performance is better than that of the dual loop control with only an acceleration loop and a position loop at low frequency.

Enhanced Disturbance Observer Based on Acceleration Measurement for Fast Steering Mirror Systems

In this paper, a modified disturbance observer (DOB) for fast steering mirror (FSM) optical system based on a charge-coupled device (CCD) and inertial sensors is proposed. Combining a DOB with the classical cascaded multiloop feedback control, including position loop, velocity loop, and acceleration loop, that the disturbance suppression performance of line-of-sight in an FSM system can be significant improved. However, due to the quadratic differential in the FSM acceleration open-loop response, in fact, it is very difficult to realize an integral algorithm to compensate a quadratic differential in practical application. Thus, the conventional DOB controller has to be simplified further to make a concession, which eventuates in still insufficient disturbance compensation, particularly at low frequency. To solve this problem, an enhanced DOB control structure, which changes the compensation plant to be the acceleration open-loop and avoids the saturation of double integration skillfully, is proposed. The recommended method optimizes the controller design, which is conducive to controller fulfillment in practical systems. A series of comparative experimental results demonstrate that the disturbance suppression performance of the FSM control system can be effectively improved by the proposed approach.

Precision laser tracking servo control system for moving target position measurement

Laser tracking and servo control is essential for the laser tracker to accurately measure coordinates and trajectories of dynamic targets in the space. It has demanding requirements for tracking performance of the servo system in terms of dynamic response properties, controlling accuracy and stability. The currently used servo controlling system in the laser tracker usually adopts the traditional proportional, integral and differential (PID) controlling methods While measuring the dynamic coordinates, the target lens move randomly in a greatly dynamic way; the system’s tracking speed faces a delay in adapting to it, resulting in frequent miss or loss of the target. Based on the requirements of the laser tracing and servo system to quickly track targets moving in a very random and dynamic manner, this paper studies the controlling properties of the laser tracking servo system and the modelling of the controlled objects, proposing a hybrid controlling structure and method which incorporates multi-loop feedback control as well as fuzzy prediction and control-based correction. The deviation signal of the photoelectric location is extracted and fuzzified. Fuzzy rules and controlling strategies are formulated. A fuzzy adaptive PID tracking control algorithm is also presented. A platform for testing the servo tracking system is constructed. The proposed controlling strategies and algorithms are applied to the single-axis laser tracking and rapid prototype tracking tests. Test results show that the angular acceleration of the dynamic tracking servo exceeds 200°/s2, proving great improvements in the system’s random dynamic tracking performance and stability.

MEMS Inertial Sensors-Based Multi-Loop Control Enhanced by Disturbance Observation and Compensation for Fast Steering Mirror System.

In this paper, an approach to improve the disturbance suppression performance of a fast steering mirror (FSM) tracking control system based on a charge-coupled device (CCD) and micro-electro-mechanical system (MEMS) inertial sensors is proposed. The disturbance observation and compensation (DOC) control method is recommended to enhance the classical multi-loop feedback control (MFC) for line-of-sight (LOS) stabilization in the FSM system. MEMS accelerometers and gyroscopes have been used in the FSM system tentatively to implement MFC instead of fiber-optic gyroscopes (FOG) because of its smaller, lighter, cheaper features and gradually improved performance. However, the stabilization performance of FSM is still suffering a large number of mechanical resonances and time delay induced by a low CCD sampling rate, which causes insufficient error attenuation when suffering uncertain disturbances. Thus, in order to make further improvements on the stabilization performance, a cascaded MFC enhanced by DOC method is proposed. The sensitivity of this method shows the significant improvement of the conventional MFC system. Simultaneously, the analysis of stabilization accuracy is also presented. A series of comparative experimental results demonstrate the disturbance suppression performance of the FSM control system based on the MEMS inertial sensors can be effectively improved by the proposed approach.

Robust Stability Analysis of Active Voltage Control for High-power IGBT Switching by Kharitonov's Theorem

The main idea of active voltage control (AVC) is to employ classic feedback-control methods forcing the IGBT collector voltage transient to follow a predefined trajectory. This feedback control of IGBTs has great advantages in guaranteeing that IGBTs remain in safe operating area (SOA), restricting EMI, mitigating the voltage/current stress, minimizing/predicting their power losses, and balancing voltages of IGBTs in series. Inevitably, however, AVC introduces stability issues. Based on the assumption that accurate IGBT small-signal model parameters are available, an analogue proportional-derivative and multiloop feedback control was proposed to achieve stable performance in previous work. Due to nonlinearities and uncertainties in IGBT parameters, previous stability analysis methods have important limitations. This work uses Kharitonov's theorem during the IGBT controlled turn-off to assess the system's stability and guide the AVC design to account for model uncertainties and varying parameters. We conducted experiments to investigate the system's robust stability due to these uncertainties in the IGBT parameters, which confirm the validity of the proposed theoretical analysis. With the use of wide bandwidth op-amps, it is shown that the feedback design may be simplified.

Dynamic control of a selective hydrogenation process with undesired MAPD impurities in the C3-cut streams

The selective hydrogenation process is commonly used to remove the undesired methylacetylene-propadiene (MAPD) in the C3-cut streams. A single-stage selective hydrogenation process, which is primarily composed of an adiabatic catalytic reactor and a heat exchanger, is performed to meet the product specifications of normally less than 300 ppm of MAPD. By taking into account the deactivation of the catalyst, the optimal operating conditions are determined by solving the time-dependent optimization algorithm for maximizing propylene yield. Based on the optimal operating trajectories, the multi-loop feedback control framework is successfully verified to achieve the liquid-phase hydrogenation process with the low outlet concentration of MAPD.

Virtual Flux Droop Method—A New Control Strategy of Inverters in Microgrids

The parallel operation of inverters in microgrids is mainly based on the droop method. The conventional voltage droop method consists of adjusting the output voltage frequency and amplitude to achieve autonomous power sharing without control wire interconnections. Nevertheless, the conventional voltage droop method shows several drawbacks, such as complicated inner multiloop feedback control, and most importantly, frequency and voltage deviations. This paper proposes a new control strategy in microgrid applications by drooping the virtual flux instead of the inverter output voltage. First, the relationship between the inverter virtual flux and the active and reactive powers is mathematically obtained. This is used to develop a new flux droop method. In addition, a small-signal model is developed in order to design the main control parameters and study the system dynamics and stability. Furthermore, a direct flux control algorithm is employed to regulate the virtual flux according to the droop controller, which avoids the use of proportional-integral controllers and pulse-width modulation modulators. Both the simulation and experimental results show that the proposed flux droop strategy can achieve active and reactive power sharing with much lower frequency deviation than the conventional voltage droop method, thus highlighting the potential use in microgrid applications.

Model predictive control of a solar-thermal reactor

This paper presents the application of a Model Predictive Control (MPC) system to a solar-thermal reactor for carbon-steam gasification. The controller aimed at rejecting the disturbances in solar irradiation, caused by the presence of clouds, through the manipulation of the flow rates into the reactor. Simulations of a first-principles dynamic model were used to fit a linear, time-invariant model, to be used directly in the MPC algorithm. The MPC was tuned through simulations, until robust control was achieved. The proposed control system was compared to a fine-tuned multi-loop feedback control strategy. Simulations of the controlled reactor system showed that the linear MPC was capable of minimizing the effect of the disturbances within the entire operating region, outperforming a more conventional multi-loop feedback strategy. The results obtained suggest that the proposed controller is suitable for a real-world implementation.

Modeling and multi-loop feedback control design of a SEPIC power factor corrector in single-phase rectifiers

In this paper, a comparative analysis of three multi-loops control schemes dedicated to the single ended primary inductance converter (SEPIC) power factor corrector (PFC) is presented. The first control technique uses a robust hysteresis current controller; the second control strategy consists of a frequency–domain linear design of regulators on the basis of a small-signal averaged model of the converter, whereas the third control design method uses the input/output feedback linearization approach applied on the large-signal state-space averaged model of the converter. In order to verify and compare the performance of all control schemes, numerical simulations are carried out on a switching-functions-based model of the converter, which is implemented using Matlab/Simulink. The control systems are tested under both rated and disturbed operating conditions. The systems performance is evaluated in terms of source current total harmonic distortion (THD), input power factor, and DC voltage regulation toward load disturbances.

Fast Acting Regenerative DC Electronic Load Based on a SEPIC Converter

A fast acting regenerative dc electronic load based on the single-ended primary inductor converter (SEPIC) converter has been implemented. A simple multiloop feedback control system has been design for the SEPIC converter to realize the main function of electronic load. Instead of discharging via resistive load, the output of the converter is connected to rechargeable batteries such that discharged energy can be saved for future use. Circuit implementation of the proposed scheme is presented and experimental results are included to demonstrate the effectiveness of the proposed design.

Multi-loop controller for wide operating range single-ended primary inductor DC/DC converter

A novel controller based on the decoupling of single-ended primary inductor converter (SEPIC) state-space averaging model to four simple first-order systems is proposed. Instead of designing a single controller for a fourth-order SEPIC converter, four PI controllers are designed for the four decoupled systems. Combining the four PI controllers with the four decoupled systems forms a multi-loop feedback control system which is able to work at a wider operating condition. Circuit implementation of the proposed controller is presented and experimental results are included to demonstrate the effectiveness of the proposed design scheme.

Control of a heat-integrated proton exchange membrane fuel cell system with methanol reforming

This work presents a novel heat-integrated fuel cell stack system with methanol reforming. Its configuration is composed of fuel processing units (FPUs), proton exchange membrane (PEM) fuel cell stack, and heat exchangers (HEXs). Well mixed methanol and oxygen flows in contact with countercurrent flowing water dominates the production of hydrogen at the exit of FPUs and influences the stack temperature. The heat exchange connections can enhance the utilization of energy of FPUs. To ensure the stable steady-state operation, the model-free fuzzy incremental control scheme within the multi-loop feedback control framework is developed. Finally, the proposed system integration and control configuration are verified by closed-loop simulations.

Role of motion cues in straight-line driving of an agricultural vehicle

Driving simulators open new opportunities for research in a wide range of areas including human factors and ergonomics. The main concern regarding driving simulator research is the validity of the results. In order to obtain the same driving behaviours as those in a real world experiment, it is necessary to provide the driver with the same sensory cues that he/she uses in real world driving. Therefore, one would like to know which sensory cues are used by the human driver. This study investigates the effect of motion cues in straight-line driving of a tractor. Field experiments were conducted in which experienced tractor drivers drove a tractor in parallel swathing mode with the help of a lightbar guidance system. Driving simulator experiments were then performed in which experienced tractor drivers drove in two sessions: in one session motion cues were provided whereas in the other session motion cues were not delivered. Analysis showed that in the absence of motion cues, the drivers significantly increase their control activity and their performance deteriorates. It is also shown that drivers are unable to respond to the full range of disturbances on the tractor and the guidance system and that they automatically reduce the open-loop crossover frequency by reducing their gain, in order to avoid high tracking errors. In the presence of motion cues, drivers adopted a more relaxed driving style by reducing their gain and lead time constant. Using a multi-loop feedback control scheme it is shown that if the driver uses both tractor lateral deviation and yaw rate as feedback variables, he/she can drive the tractor without any lag or lead equalization. The results show that driving simulators for agricultural vehicles require a motion subsystem to allow valid duplication of the real field driving in parallel swathing mode. The implications of the results of this study for developers of guidance systems are also discussed.

A CRITERION OF A MULTI-LOOP OSCILLATOR CIRCUIT

Multi-loop feedback control has attracted considerable attention due to its simplicity and ease of implementation.1 In order to simplify the cumbersome analysis of a multi-loop circuit, the signal flow graph representation should be used rather than our familiar nodal analysis methods. This paper presents a criterion from the well-established Mason's formula for multi-loop oscillator in terms of signal flow graphs. The multi-loop oscillator circuit based on two operational transresistance amplifiers (OTRAs) is used as an example.

A multiobjective-optimal neuro-fuzzy extension to power plant co-ordinated control

This paper presents an overall control scheme for wide-range multiobjective-optimal operation of a fossil-fuel power unit. The scheme provides the means to accommodate operating scenarios characterized by multiple operating requirements, and to attain optimal operation along any arbitrary unit load-demand pattern. The proposed strategy builds upon current co-ordinated control schemes, which typically account for simultaneous control of power and steam pressure. First, the scope of co-ordination over the internal processes of the unit is extended by including the control of the drum water level to achieve balanced overall plant operation at all loads. Then, a supervisory reference governor and a neuro-fuzzy feedforward control path are added to complement the already existing multiloop feedback control configuration. The reference governor implements a set-point scheduler based on unit load demand to set-point mappings, which are designed by solving a multiple objective optimization problem. The feedforward control path approximates the nonlinear multivariable inverse static behaviour of the power unit at the optimal operating conditions specified by the set-point mappings through a set of multi-input-single-output fuzzy inference systems, which are designed using a neuro-fuzzy learning paradigm. With this approach, the plant is driven by an arbitrary unit load-demand pattern from which the reference governor specifies the multiobjective-optimal operating conditions for the plant through set-point trajectories; the feedforward control path provides control signals to achieve wide-range manoeuvrability and the feedback control path compensates for uncertainties and disturbances, along and around the commanded set-point trajectories, respectively. Simulation results demonstrate the feasibility of the proposed control scheme.

Multi-loop feedback control of offshore steel jacket platforms

In this paper, a new multi-loop feedback-control design is developed and applied to an offshore steel jacket platform. The platform is subjected to wave-induced self-excited hydrodynamic forces. The nonlinear Morison equation is employed to estimate these wave forces. The feedback control design proceeds in two consecutive loops: an inner loop for regulating a linear part of the platform dynamics and an outer loop to accommodate the nonlinearities while maintaining the overall stability. A SIMULINK model is designed to simulate the response of a three-floor steel jacket platform example. Results of the simulation of this structure with and without feedback-control are discussed to demonstrate the effectiveness of this control method.

Process laboratory — A necessary resource in control engineering education

Our experiences from continuing education on the field of industrial process control show that the control engineering courses for an industrial staff are much more interesting and more useful when they are practically oriented. That was one of the reasons to build a process laboratory that consists of a pilot chemical plant highly equipped with industrial sensors and actuators, different industrial controllers and monitored by a computer control system. A process laboratory serves a number of purposes: development and application, research, training and education. The technological process equipment is fully supplied with industrial control elements so the great number of different real-life experiments can be performed. Modern control equipment assures that a variety of contemporary control techniques and metodologies (feed-forward control, single and multiloop feedback control, advanced control, etc.) can be tested and implemented. The paper describes in detail the configuration of the process laboratory, its control system and the software tools used during the educational process.