Multi-input Multi-output Sliding Mode Control Research Articles

A novel MIMO SMC for comprehensive unified control of the cascaded DC‐DC and DC‐AC converters in grid connected photovoltaic systems

SummaryIt is well known that DC‐DC boost converters are cascaded with DC‐AC inverters for grid connection of the photovoltaic (PV) systems. In the traditional control approaches, the mentioned DC‐DC and DC‐AC converters are controlled separately to facilitate the controller design problem. However, from the controller design viewpoint, the overall structure of the grid connected PV generator is a multi‐input multi‐output (MIMO) system. The duty cycle of the DC‐DC converter and inverter modulation index are the control inputs and, on the other hand, generated photovoltaic DC power and exported power to the grid are control outputs. Moreover, the inverter DC link voltage should be stabilized by the closed‐loop controller as well as an internal control output. If controllers are designed separately, it means that the interaction between DC‐DC and DC‐AC controllers isn't considered accurately, and since the isolated models of DC‐DC converter and DC‐AC inverter are extracted based on some approximated assumptions, separate controller design cannot guarantee stability and robustness of the whole system in a wide range of operation. To cope with these problems, in this paper, a novel MIMO sliding mode controller (SMC) is developed for comprehensive closed‐loop control of the DC‐DC boost converter cascaded with a single‐phase DC‐AC grid connected photovoltaic inverter. In the proposed approach, the dynamic model of whole system is developed comprehensively at first, and then, a unique MIMO controller is designed to control both DC‐to‐AC and DC‐to‐DC converters together. To cope with the nonlinear characteristic of the system and uncertainty of model parameters in a wide range, a fixed‐frequency SMC is developed using the comprehensive state space model of the closed loop system. In the proposed MIMO‐SMC controller, the AC power (which is exported to the grid) and operating point of the PV source are controlled via inverter modulation index and duty cycle of the DC‐DC boost converter, respectively. Another major advantage of the proposed system is mitigating the non‐minimum phase characteristic of the boost converter through the indirect control of inverter DC link capacitor. To evaluate the performance of the designed control system, simulation results are compared with a standard linear PI controller. It is shown that the developed system has zero steady‐state error and enjoys faster dynamic response during the start‐up and step changes of AC and DC current references. Moreover, it can maintain the stability of closed‐loop systems in a wide range of operations.

Multi-Input Multi-Output Sliding-Mode Control of LCL-based Grid-Connected Modified Y-Source Inverter for Power Conditioning of Photovoltaic Generation

Multi-Input Multi-Output Sliding-Mode Control of LCL-based Grid-Connected Modified Y-Source Inverter for Power Conditioning of Photovoltaic Generation

Control of sound transmission into a hybrid double-wall sandwich cylindrical shell

A 3D analytical model is formulated for diffuse sound field transmission control through a smart hybrid double concentric sandwich circular cylindrical shell structure in presence of external and internal air gap mean flows. The multi-input multi-output sliding mode control is applied to enhance the sound transmission loss characteristics via direct control action of a uniform force piezoelectric actuator layer along with semi-active variation of the stiffness/damping characteristics of the electrorheological fluid core layer incorporated in a non-collocated configuration within the external or internal shell structure. Extensive numerical simulations examine the uncontrolled/controlled diffuse field sound transmission loss spectrums in a broad frequency range for single-wall and hybrid double-wall sandwich shells at selected external and air gap Mach numbers. The proposed smart hybrid active/semi-active double-wall configuration is demonstrated to provide satisfactory overall acoustic insulation control performance with much lower operative energy requirements. Limiting cases are considered, and validity of the formulation is verified against the available data.

Fuzzy logic compliance adaptation for an assist-as-needed controller on the Gait Rehabilitation Exoskeleton (GAREX)

Assist-as-needed control strategy is an emerging approach to improve the effectiveness of gait rehabilitation training. We have proposed a pneumatic muscle (PM) driven Gait Rehabilitation Exoskeleton (GAREX) implemented with a multi-input–multi-output (MIMO) sliding mode control system to actively adjust the assistance level provided during gait rehabilitation. To realize the assist-as-needed control strategy, a specific algorithm is imperative to assess the active participation or effort of wearers and adapt the amount of assistance accordingly. We sought to establish a fuzzy logic compliance adaptation (FLCA) controller to form a novel cascade control system. We evaluated the feasibility of implemented FLCA controller on the performance of adjusting the compliance of GAREX’s knee joint according to the online assessment of the wear’s active participation level once in every gait cycle. Using controlled, treadmill-based walking tests involved three healthy subjects, we demonstrate that FLCA controller could effectively distinguish the capability/effort levels of wearers and enable the exoskeleton to adapt the knee joint compliance accordingly. Obtained results reveal that FLCA controller can collaborate well with MIMO sliding mode controller in a system and indicate the novel method of realizing assist-as-needed concept with the pneumatic muscle powered mechanisms.

Sound transmission control through a hybrid smart double sandwich plate structure

A three-dimensional analytical model is developed for control of sound transmission through an acoustically baffled simply supported hybrid smart double sandwich panel partition of rectangular planform. The hybrid structure includes spatially distributed piezoelectric (PZT) and electro-rheological fluid (ERF) actuator layers arranged in a non-collocated configuration in the incident or transmitted panels. The basic formulation utilizes the relevant classical thin plate theories, Kelvin-Voigt viscoelastic damping model, Maxwell’s equations of electrodynamics, and the linear acoustic wave equations coupled by the pertinent structure/fluid compatibility relations. The conventional multi-input multi-output sliding mode control (MIMOSMC) strategy is subsequently applied to improve the sound transmission loss (STL) through the composite partition by smart (semi-active) variation of the stiffness/damping characteristics of the ERF core layer in collaboration with the (active) uniform force PZT actuator layer according to the control commands. Extensive numerical simulations present both the uncontrolled and controlled STL performances of the composite sandwich structure for four different arrangements of the active and semi-active control elements (i.e. PZT/PZT, ERF/ERF, ERF/PZT, and PZT/ERF) as well as for the single partition (ERF, PZT) sandwich panels at selected incident angles and air cavity dimensions. Four different types of vibroacoustic resonances for the composite structure are identified and briefly discussed, namely, the mass-air-mass resonance, the sandwich panel resonances, the cavity standing-wave resonances, and the coincidence resonance. The remarkable overall advantages of all four MIMOSMC-based double panel control configurations in significant attenuation of sound transmission at very low frequencies, and in the vicinity of the coupled mass-air-mass resonances as well as at the panel resonance frequency dips, are demonstrated. In particular, the proposed hybrid smart double panel (ERF/PZT or PZT/ERF) configuration (which integrates the high performance, precision, and capability of the active PZT-based panel with simplicity, reliability, and stability robustness of the semi-active ERF-based panel) is observed to display a considerably smoother broadband sound proof ability in comparison with the conventional full active (PZT/PZT) system. More importantly, it is particularly capable of delivering up to 90% of the full active control performance, with inherently less energy and actuation demands. Limiting cases are considered and validity of the formulation is rigorously confirmed by comparison with the FEM results as well as with the available data.

Multi-Input Multi-Output-Based Sliding-Mode Controller for Single-Phase Quasi-Z-Source Inverters

In this article, a multi-input multi-output sliding mode control methodology with constant switching frequency for single-phase quasi-Z-source inverters (qZSI) is proposed. The mathematical model of the entire system is derived in state-space form. The proposed sliding mode control is capable of controlling both dc and ac sides of the system concurrently. Unlike the existing methods, the proposed control does not require proportional-integral controller in the dc-side. Furthermore, it offers several advantages, such as simple implementation, reduced gain requirement, robustness against system parameters, and zero steady-state error in the load voltage. The fixed switching frequency is attained by altering the sliding manifold behavior inside a boundary layer. The power balance equation is used to generate the dc-side inductor current reference. The feasibility of the proposed control method is investigated experimentally when qZSI feeds linear and nonlinear loads.

Design of a nonlinear multi-input–multi-output sliding mode pitch angle and plunge controller for a 5MW wind turbine blade tip

ABSTRACTTraditionally, wind turbine blades are primarily controlled by varying the pitch angle of the full blade. The primary motivation of this article is to develop a design of a nonlinear multi-input–multi-output sliding mode controller for tracking the pitch angle and the plunge of the wind turbine blade tip instead of controlling the entire blade. The hypothesis is that controlling the pitch and plunge for a portion of blade tip length can be an alternate control strategy. A method was adopted wherein a separated pitch angle control at the tip (SePCaT) was modeled and tested in a digital environment and controller response was realized by modeling desired pitch angle and plunge trajectories to abate power generated by the wind turbine to rated power at high wind speeds. From the comparative results with the desired trajectory, it was observed that the sliding mode controller exhibited excellent trajectory tracking for controlling the blade pitch angle and plunge. It can be concluded that controlling blade plunge is essential to maintaining desired blade pitch angle trajectories. This technology offers significant improvement over other technologies as desired pitch and plunge control is achieved over a shorter blade length.

MIMO Sliding Mode Controller for Gait Exoskeleton Driven by Pneumatic Muscles

In the past decade, pneumatic muscle (PM) actuated rehabilitation robotic devices have been widely researched, mainly due to the actuators’ intrinsic compliance and high power to weight ratio. However, the PMs are highly nonlinear and subject to hysteresis behavior. Hence, robust trajectory and compliance control are important to realize different training strategies and modes for improving the effectiveness of the rehabilitation robots. This paper presents a multi-input–multioutput sliding mode controller, which is developed to simultaneously control the angular trajectory and compliance of the knee joint mechanism of a gait rehabilitation exoskeleton. Experimental results indicate good multivariable tracking performance of this controller, which provides a good foundation for the further development of assist-as-needed training strategies in gait rehabilitation.

Modeling and Control of Contouring Errors for Five-Axis Machine Tools—Part II: Precision Contour Controller Design

Abstract The accurate tracking of tool-paths on five-axis CNC machine tools is essential in achieving high speed machining of dies, molds, and aerospace parts with sculptured surfaces. Because traditional CNCs control the tracking errors of individual drives of the machine, this may not lead to desired contouring accuracy along tool-paths, which require coordinated action of all the five drives. This paper proposes a new control approach where the tool tip and tool orientation errors, i.e., the contouring errors, are minimized along the five-axis tool-paths. The contouring error and kinematic model of the machine, which are presented in Part I of the paper, are used in defining the plant. A multi-input–multi-output sliding mode controller, which tries to minimize path tracking and path following velocity errors, is introduced. The stability of the system is ensured, and the proposed model is experimentally demonstrated on a five-axis machine tool. The path errors originating from the dynamics of five simultaneously active drives are significantly reduced.

Combined DAE and Sliding Mode Control Methods for Simulation of Constrained Mechanical Systems

In dynamic analysis of constrained multibody systems (MBS), the computer simulation problem essentially reduces to finding a numerical solution to higher-index differential-algebraic equations (DAE). This paper presents a hybrid method composed of multi-input multi-output (MIMO), nonlinear, variable-structure control (VSC) theory and post-stabilization from DAE solution theory for the computer solution of constrained MBS equations. The primary contributions of this paper are: (1) explicit transformation of constrained MBS DAE into a general nonlinear MIMO control problem in canonical form; (2) development of a hybrid numerical method that incorporates benefits of both Sliding Mode Control (SMC) and DAE stabilization methods for the solution of index-2 or index-3 MBS DAE; (3) development of an acceleration-level stabilization method that draws from SMC’s boundary layer dynamics and the DAE literature’s post-stabilization; and (4) presentation of the hybrid numerical method as one way to eliminate chattering commonly found in simulation of SMC systems. The hybrid method presented can be used to simulate constrained MBS systems with either holonomic, nonholonomic, or both types of constraints. In addition, the initial conditions (ICs) may either be consistent or inconsistent. In this paper, MIMO SMC is used to find the control law that will provide two guarantees. First, if the constraints are initially not satisfied (i.e., for inconsistent ICs) the constraints will be driven to satisfaction within finite time using SMC’s stabilization method, urobust,i=−ηisgnsi. Second, once the constraints have been satisfied, the control law, ueq and hybrid stabilization techniques guarantee surface attractiveness and satisfaction for all time. For inconsistent ICs, Hermite-Birkhoff interpolants accurately locate when each surface reaches zero, indicating the transition time from SMC’s stabilization method to those in the DAE literature. [S0022-0434(00)02404-7]