Complicated Control Design Research Articles

Model Predictive Control-Based Dual-Mode Operation of an Energy-Stored Quasi-Z-Source Photovoltaic Power System

The energy-stored quasi-Z-source inverter (ES-qZSI) has attracted much attention for photovoltaic (PV) power generations, due to its capability to stabilize the PV power fluctuations with simple structure and other advantages of Z-source inverter. The improved dual-mode (DM) ES-qZSI is able to support all-weather operation even at night or cloudy days when PV power is extremely low. Whereas, the traditional proportional-integral (PI) based control suffers from complicated controller design and poor dynamic response during mode transition, due to two sets of PI control required for the daytime and night operation modes. In order to overcome that, this paper proposes a model predictive control strategy for the DM-ES-qZSI PV power system. The system predictive models in both day and night operating modes are derived. The control strategy is disclosed to ensure high performance of the system, through calling the predictive models and defined cost functions of the two modes within a single control loop. Simulation and experiment are carried out to verify the effectiveness of proposed control strategy.

Research on LADRC of Grid-Connected Inverter Based on LCCL

A grid-connected inverter’s stability is easily influenced by the system’s internal and external characteristics, especially when the grid-connected inverter is connected to the grid by an LCL filter, which complicates the system design and operating conditions. To handle the problem of disturbance in the high-order grid-connected system of the inverter, a linear active disturbance rejection control (LADRC) strategy based on LCCL (which divides the capacitor of the LCL filter into two halves in a specified proportion) is proposed in this paper. First, the system is reduced from third order to first order by using the split capacitor control method, which solves the difficulties of complicated LCL grid-connected inverter controller design and easy resonance. Meanwhile, the internal and external disturbances of the inverter system are treated as generalized disturbances. Then, the LADRC control is used to adjust the closed-loop system’s parameters, which enhances the quality of the grid current and the system’s stability. Finally, the impacts of PI and LADRC control on the power mutation and voltage drop of an LCCL grid-connected inverter are compared by the experiments. The experimental results show the effectiveness of the proposed LADRC control strategy.

A direct analytical predetermination of PMSG based WPS steady-state values under different operating conditions

This paper presents a direct analytical method to predetermine the steady-state values of a permanent magnet synchronous generator (PMSG) based wind power system (WPS) at each stage of power flow. A generalized structured is developed with two independent equivalent circuits, that is, PMSG and grid side. To effectively determine the converters performance numerals despite grid disturbances, steady-state model is structured with positive sequence components of grid voltage. The advantage of the proposed model is that the methods evade the requirements of d-q modeling and a dedicated controller to evaluate the system performance. Using the proposed steady-state model, the entire WPS components ratings is predicted evading time domain simulation with complicated controller design. Also, the simple controller design is proposed to aid in optimal power flow supplement with FRT requirements under all possible system operating conditions. Ultimately, validation of predetermined values with the simulated PSCAD/EMTDC response including the proposed controller is investigated.

Decoupled tracking and damping control of piezo-actuated nanopositioner enabled by multimode charge sensing

Precision motion control of piezo-actuated nanopositioners has attracted considerable attention, due to their wide acceptance in precision engineering. However, several challenging issues, such as hysteresis and creep effects along with mechanical resonances, often lead to a complicated controller design. In this paper, we show that the control strategy can be significantly streamlined by a multimode charge sensing scheme (MCSS). MCSS consists of two different position estimation approaches, namely, inflow charge sensing (ICS) and force induced charge sensing (FICS). Treating piezo-actuated nanopositioner as a standard Hammerstein system, MCSS enables the measurement of intermediate variable, and hence offers a new possibility to divide a challenging control issue into two much easier ones. This is the central idea of the proposed decoupled tracking and damping control (DTDC) strategy. DTDC exhibits several outstanding characteristics, including simple configuration, unconditional stability and wide control bandwidth. Experimental validations on a customized nanopositioner confirm these advantages that MCSS brings to the controller design. Finally, extensive comparative studies demonstrate a good trade- off between control accuracy and complexity of the proposed strategy.

High accuracy disturbance observer-based agile attitude stabilization with three-dimensional MSW

PurposeThe purpose of this paper is agile attitude control design with the novel three-dimensional (3D) magnetically suspended wheel (MSW) that is the preferred type for agile maneuvering compared to conventional control moment gyro due to frictionless, low vibration and long lifetime. This system does not require a separate steering law for pyramid arrangement to derive tilt angles. It is also conducting an agile maneuver with high accuracy despite the high-frequency disturbances.Design/methodology/approachIn this paper, a disturbance observer-based attitude stabilization method is proposed for an agile satellite with a pyramid cluster of the novel 3D magnetically suspended wheel actuator. This strategy includes a disturbance observer and a linear quadratic regulator controller. The rotor shaft deflection of MSW is actively controlled to reduce vibration and producing gyro torque. The deflection angle of the pyramid cluster MSWs considered as control parameters. The closed-loop stability is proved by using the Lyapunov strategy. The efficiency and performance of the offered method verified by numerical simulation via MATLAB/SIMULINK software.FindingsAccording to simulation results, the disturbance observer-based control controller stabilized the system with high accuracy and optimal tilt angles without any extra steering law equation. Hence, the system speed is increased, and the system error is minimized without separate steering law.Practical implicationsThe magnetically suspended wheel is a new kind of inertia actuator for attitude control that has several benefits such as frictionless, high-speed rotor, clean environment and low vibration compared to the traditional wheel. It has complex nonlinear dynamics that cause have complicated controller design. The proposed strategy stabilizes the system and conducting an agile maneuver with high precision despite the high-frequency disturbances. It is applicable for some missions requiring high accuracies, like Earth observation and the solar observation mission that require a very accurate pointing control and a long lifetime.Originality/valueThis paper is the initial paper to design a pyramid array for magnetically suspended wheels. Compared to other research, this method doesn’t need a separate steering law of the MSWs cluster and presented optimal tilt angles with less computational. Also, it designs a disturbance observer-based controller for this system that proposed high accuracy and agile stabilization.

NCTF Control Performance Analysis on Rehabilitation Robot

The need for rehabilitation robots is increasing, while the current price is too high. One reason for the high price of rehabilitation robots is the complicated controller design. For this reason, there is a need for a simpler controller design to be produced at an affordable price. In this study, the NCTF control system tested its performance on a rehabilitation robot prototype with a horizontal linear motion system. The tests are carried out using point to point and set point tracking commands. Point to point testing is carried out at a distance of 50 mm, 150 mm and 230 mm. Meanwhile, set point tracking testing was carried out on the sinusoidal wave with a 100 mm amplitude and a frequency of 0.25 Hz. Both tests were carried out by giving a load of 0 Kg, 0.82 Kg, and 1.64 Kg. The results of this study indicate that the NCTF control provides a good response. The steady-state error value for all point to point motion commands below 2%. As for set point tracking commands, the system can follow orders properly, but there is a 0.24-second delay.

Dual-Input Isolated Converter With Dual-Charge-Pump Cell for High Step-Up Voltage Ratio Achievement

In this article, a novel dual-input isolated converter (DI2C) is proposed, which can process two different kinds of clean energy and possesses the features of galvanic isolation and high voltage gain. A dual-charge-pump cell is also proposed in this article and then immersed into the power stage to achieve a high step-up voltage ratio and recycle the energy of leakage inductance. Based on the configuration of the DI2C, even if either of the input sources is interrupted, the converter still can function and keep the high step-up feature. The DI2C only requires two active switches and two coupled inductors. Therefore, the power stage is concise, avoiding complicated control design and simplifying driver mechanism as well. The operation principle, theoretical analysis, and mathematical derivation are thoroughly described. A 200-W prototype is built and then tested to corroborate the correctness of the theoretical analysis and the feasibility of the proposed converter. The measured efficiency is 92.4% at full load.

Energy Saving Motion Control of Independent Metering Valves and Pump Combined Hydraulic System

The independent meter-in and meter-out valves control approach makes the two chamber pressures of the hydraulic actuator completely controllable, and offers possibilities for energy conservation. However, the entire flow rate is throttling controlled by the metering valves, which leads to the essential difficulty to realize the high level of energy efficiency further. On the other hand, although the direct pump controlled system might be an option with high energy efficiency, the poor dynamic response, and complicated controller design restrict its applications in precise motion occasions. To further improve the energy efficiency as well as guarantee the high precision position tracking performance, a novel hardware configuration that combines the independent metering valves and the direct pump control method is proposed in this paper, which is essentially different from our previous works and other independent metering research works. The motion control of the single-DOF cylinder actuator is studied to verify the effectiveness and advantages of the proposed system. During the tracking process, the pump is controlled by the reference velocity feedforward method and provides the majority amount of the flow rate without throttling losses, while the rest amount is accurately controlled by the independent metering valves in the closed loop for high precision tracking. Since the hydraulic system is highly nonlinear with uncertainties and disturbances, the high-performance adaptive robust control approach is applied in the closed-loop controller. Besides, the mode selection method and the flow distribution law are involved to deal with the enhanced flexibilities brought by the proposed configuration.Comparative experiments are carried out and the results show the proposed combined hydraulic system achieves the same level of position tracking precision as the independent metering system with less than a half of total energy consumption.

A comparative study of hybrid simulation and dynamical substructuring system schemes for shake table tests

In shaking table experiments, the dynamics of the shake table is strongly affected by a specimen to be tested, particularly when the specimen is very heavy. This is also the case when substructuring experiments are implemented by the shaking tables. This study numerically examines two substructuring schemes applied in shaking table experiments. Hybrid simulation scheme, which is commonly used in substructuring experiments, directly uses the output of the numerical substructure as the input to the physical substructure. Dynamical substructuring system (DSS) scheme, which requires more complicated control design, determines the control input to minimize control error obtained by outputs of numerical and physical substructures. This study has found that, in shaking experiments, the stability of the hybrid simulation scheme is very sensitive to a pure time delay. It is also found that DSS scheme can provide much higher stability margin against the pure time delay than the hybrid simulation scheme. The effort to rather complicated controller design of DSS scheme will be rewarded at actual control practices.

Flight Test Data Analysis of Hybrid Vertical Take-off and Landing Unmanned Aerial Vehicle

Abstract —A Hybrid Unmanned Aerial Vehicle (UAV) has both advantages of multirotor and fixed-wing UAV. This unique design leads to a more complicated airframe and control design compared to those of a conventional drone. Integrating two platform of UAV (mutirotor and fixed-wing) also requires carefully consideration to safely operate this hybrid UAV. This paper discussed the flight scenario that includes flight modes and parameters to be determined before flight. This leads to the development of the flight procedure as an important prerequisite for a successful flight.

Distributed adaptive switching consensus control of heterogeneous multi-agent systems with switched leader dynamics

In this paper, the leader-following distributed consensus control problem is addressed for general linear multi-agent systems with heterogeneous uncertain agent dynamics and switched leader dynamics. Different from most existing results with a single linear time-invariant (LTI) leader dynamics, the leader dynamics under consideration is composed by a family of LTI models and a switching logic governing the switches among them, which is capable of generating more diverse and sophisticated reference signals to accommodate more complicated consensus control design tasks. A novel distributed adaptive switching consensus protocol is developed by incorporating the model reference adaptive control mechanism and arbitrary switching control technique, which can be synthesized by following a two-layer hierarchical design scheme. A numerical example has been used to demonstrate the effectiveness of the proposed approach.

State-Space Adaptation of Unsteady Lifting Line Theory: Twisting/Flapping Wings of Finite Span

In this paper, a low-order state-space adaptation of the unsteady lifting line model has been analytically derived for a wing of finite aspect ratio, suitable for use in real-time control of wake-dependent forces. Each discretization along the span has between 1–6 states to represent the local unsteady wake effects, rather than remembering the entire wake history which unnecessarily complicates controller design. Sinusoidal perturbations to each system degree of freedom are also avoided. Instead, a state-space model is fit to individual indicial functions for each blade element, allowing the downwash and lift distributions over the span to be arbitrary. The wake geometry is assumed to be quasi steady (no roll up) but with fully unsteady vorticity. The model supports time-varying surge (a nonlinear effect), dihedral, heave, sweep, and twist along the span. Cross-coupling terms are explicitly derived. This state-space model is then validated through comparison with an analytic solution for elliptic wings, an unsteady vortex lattice method, and experiments from the literature.

Single-Stage AC/DC Single-Inductor Multiple-Output LED Drivers

Various ac/dc LED driver topologies have been proposed to meet the challenges of achieving a compact, efficient, low-cost, and robust multistring LED lighting system. These LED drivers typically employ a two-stage topology to realize the functions of ac/dc rectification and independent current control of each LED string. The choice of having two stage conversions involves additional hardware components and a more complicated controller design process. Such two-stage topologies suffer from a higher system cost, increased power loss, and large form factor. In this paper, a single-stage ac/dc single-inductor multiple-output LED driver is proposed. It uses only one single inductor and N + 1 active power switches ( N being the number of LED strings) with reduced component count and smaller form factor. The proposed driver can achieve both functions of ac/dc rectification with a high power factor and precise independent current control of each individual LED string simultaneously. A prototype of an ac/dc single-inductor triple-output LED driver is constructed for verification. Experimental results corroborate that precise and independent current regulation of each individual LED string is achievable with the proposed driver. A power factor of above 0.99 and a peak efficiency of 89% at 30-W rated output power are attainable.

Low-frequency dynamic modelling and control of matrix converter for power system applications

High-power density of a matrix converter (MC) necessarily introduces tight dynamic input–output coupling, which complicates controller design for high bandwidth applications. Strong contemporary interest in MC-based solutions for synchronous, power system applications demands high dynamic performance out of the MC, operated as a closed-loop system. The requisite system models reported either treat the MC – with its input and output filters – as a ‘black-box’ characterised by a set of eigenvalues, derived from linearised analysis around an equilibrium point. Alternatively, large-signal system analysis was reported for a feed-forward control approach with prescription of a throughput power boundary for stable operation. This study provides a designer's insight into MC modelling, based on linearised analysis, clearly establishing the influence of individual physical sub-systems on the overall dynamic performance. Onset of a cluster of right-half zeros, decided solely by the input filter, power factor, source voltage and power throughput, is shown to be the only factor threatening closed-loop stability. Subsequently, a controller with output feedback is designed to ensure stable operation well beyond the throughput power limit prescribed earlier. Comprehensive simulation and experimental results are provided to validate the analytical model and controller design.

Control of a direct internal reforming molten carbonate fuel cell system using wavelet network-based Hammerstein models

Inspired by a direct internal reforming molten carbonate fuel cell (DIR-MCFC) coupled with complicated nonlinear dynamics, the identification and control design of the Hammerstein model is presented. Through the sequential identification procedure, the static nonlinearity block is considered as the wavelet network which is trained and validated by the on-line learning algorithm, and the linear dynamic block is described by the state-space model in which parameters are estimated by the recursive least square algorithm. Using the numerical interpolation technique to approximate the implicit nonlinear function, we present a composite control framework consists of a nonlinear inversion and linear control. Through the closed-loop simulation tests, the nonlinear inversion design for the nonlinearity cancellation of a class of nonlinear systems is validated.

Towards Dual MPC

Abstract We present a novel approach to performing closed-loop system identification with minimal deterioration of output regulation. The adaptive control algorithm excites the system to improve model identification but does not disturb the plant when parameter estimates are good, so that a balance between output regulation and excitation for identification is found without requiring persistent excitation. The formulation of the problem is such that standard state-of-the-art optimization codes can be used in the controller rather than techniques like stochastic dynamic programming, which may lead to a more complicated control design. The approach is based on model predictive control (MPC) and can be implemented with only minor modifications to an existing MPC algorithm. The method is illustrated on an example system where the input gain is unknown, and is shown to intelligently excite the system only when the parameter estimates are uncertain. We also show how a slight increase in system excitation by the controller can greatly enhance parameter identification with minimal effect on the system output.

Identification and Control of a fuel cell system using wavelet network-based Hammerstein models

Inspired by a direct internal reforming molten carbonate fuel cell (DIR-MCFC) coupled with complicated nonlinear dynamics, the identification and control design of the Hammerstein model is presented. Through the sequential identification procedure, the static nonlinearity block is considered as the wavelet network which is trained and validated by the on-line learning algorithm, and the linear dynamic block is described by the state-space model in which parameters are estimated by the recursive least square algorithm. When a nonlinear inversion via the numerical interpolation technique is established, a composite control framework is used to ensure the good output regulation.

Genetic Algorithm-based Modeling and Optimization of Control Parameters of an Air Motor

Challenging optimization problems, which elude acceptable solutions via conventional methods, arise regularly in control systems engineering. Genetic algorithms are applied here to optimize the control gains for a controller of a pneumatic drive. We show that, by using minimum information specific to the system, near optimal values of the control gains can be obtained within 10 generations. Two main motivating factors are behind this kind of study; namely, the response of pneumatic drives is very slow, which leads to its inability to attain set points due to high hysteresis. Moreover, the dynamic model of the system is highly nonlinear, which greatly complicates controller design and development. To address these problem areas, two streams of research efforts have evolved—using conventional methods and adopting a strategy that does not require a mathematical model of the system

Optimal truncated model for vibration control design within a specified bandwidth

The work in this paper is directed at developing correction terms for a truncated structural dynamic model, which includes the effect on the structural response of both low and high frequency unmodelled vibration modes. The proposed model correction approach considers the corrected truncated model that only takes into account resonant modes within the bandwidth of interest and the optimised correction terms. The proposed approach is in contrast to the standard model correction approach that normally utilises a feedthrough correction term, taking into account only the unmodelled high frequency modes, while including all low frequency resonant modes into the truncated model. Thus, when one only interested in controlling vibration associated with a specified bandwidth of interest, the order of the corrected truncated model can be kept sufficiently low since the model does not have to include low and high frequency modes, leading to less complicated control design problems. Such active control within the specified bandwidth can be crucial for control tasks in the vibration minimisation at localised structural regions or in the noise reduction due to some coupled structural–acoustic modes. The procedures for calculating the optimal correction terms which include the lower and higher order mode contributions are outlined for both analytical and experimental models, allowing the procedures to be used for a wide range of theoretical and practical applications.

An evolutionary approach to active suspension design of rail vehicles

This paper presents an application of a constrained multiobjective evolutionary algorithm for the design of active suspension controllers for light rail vehicles with the aim of providing superior ride comfort within the suspension's stroke limitation. A multibody dynamic model of a three‐car train is derived and the control parameters are optimized. Force cancellation, skyhook damper, and track‐following are used to synthesize the active controller. Selection of the active suspension parameters is aided by an evolutionary computation algorithm to get the best compromise between ride quality and suspension deflections due to irregular gradient tracks. An evolutionary multiobjective optimization approach accompanied with the Pareto set is proposed to deal with the complicated control design problem.