Modal Control Theory Research Articles

Adaptive selective-invariant control of tracking electric drives with elastic kinematic transmissions

Currently, high quality indicators of adaptive versions of selective-invariant electromechanical systems designed to control the speed in a wide range have been obtained. Thus, it lays the groundwork for effective use of the proposed synthesis methods and obtained structural solutions in the systems of contour-positional and tracking control of angular displacements of the working elements of technological machines. The implemented structural-parametric synthesis is based on the methods of the theory of modal control, reduction of regulators, the principles of selective invariance, separation of the rates of movement of local subsystems, adaptive, contour-positional and tracking control. The study has been carried out by detailed computational experiments with models of synthesized electromechanical systems. The features of synthesis and functioning of adaptive selective-invariant systems with elastic kinematic links in the tracking and positioning modes are described. The combination of the principles of tracking, selective-invariant and adaptive control in the structure of a single electromechanical system makes it possible to fully provide new opportunities for the implementation of high-precision dynamic control of working machines.

Modal space neural network compensation control for Gough-Stewart robot with uncertain load

This paper investigates the motion control of a Stewart parallel robot with uncertain load. The external disturbances caused by load can trigger dynamic coupling among six degree-of-freedoms and have a significant impact on control precision. In practice, the dynamic parameters of load is difficult to be precedent identified and the robot with load is a multi-input multi-output(MIMO) system in physical space, which makes the dynamic coupling problem difficult to solve effectively and the high-performance control is hard to achieve. In this paper, the dynamic effect of the load is first analyzed. Then a novel motion control method, modal space neural network compensation control, is designed with the aim of reducing the effect of the load disturbances. This controller implements the neural network to compensate for the load disturbances. In addition, the modal space control theory is introduced to realize the independent control of each control channel. The feasibility of the proposed controller is evaluated in numerical simulations. Results reveal that the proposed control method gives exceptional tracking performance and dynamic coupling suppression capability.

Development and research of selectively invariant electromechanical systems with elastic kinematic units based on the separation of the harmonic disturbance model

Currently there is a big variety of structure solutions of the selective invariant electromechanical systems with different layout schemes of disturbance internal model for electric drives with robust kinematic units. However, methods of structural parametric synthesis for controllers with combined triggering model only were developed selective invariant systems with “robust” kinematic of mechanical part. Consequently, further improvement of the structure variety of systems for special effects of elastic kinematic units of mechanical part is of current interest. It can be performed by including the distributed model of harmonic disturbance into the synthesis process. Structural parametric synthesis is based on the methods of modal control theory, regulators reduction, selective invariant principals, velocity separation in local sub-systems, regulation by coordinates of state and by output, cascade and slaved coordinates regulation, splitting of disturbance model to separate elements in managing contours. Investigation was performed by specified computing experiments with synthesized electromechanical system models. Now, new structure solutions of selective invariant electromechanical systems with elastic mechanical elements are developed. They are created by using the additional separation principle for disturbance model into separate parts and moving them in to the contours of “fast” and “slow” sub-systems. Acquired models of synthesized systems were compared upon the complex of main quality indicators, the comparison was based on the performed computing experiments. The acquired results of complex performance of set requirements demonstrate main pros and cons for each variant of selective invariant electromechanical systems with elastic elements, determine areas of their preferred usage and allow the developers to simplify the solution of structure optimization based on selected schema of compromises.

Newton’s iterative formula for finding an equation solution as an abstract problem of the modal synthesis theory

A new approach to obtain an iterative Newton formula for finding an equation solution, by using modal control theory for linear discrete systems when solving problems of observation or identification is presented. The decomposition method as a modal control method, which allows obtaining analytical solutions, is used. Keywords Newton’s iterative formula; numerical solution of the equation; decomposition method of modal synthesis; linear discrete system

Damping of Subsynchronous Resonance in a Hybrid System With a Steam-Turbine Generator and an Offshore Wind Farm Using a Unified Power-Flow Controller

This article proposes a unified power-flow controller (UPFC) to suppress subsynchronous resonance occurred in a hybrid power-generation system connected to an infinite bus through a series-capacitor compensated line. The hybrid power-generation system contains a steam-turbine generator (STG) and an offshore wind farm (OWF) based on doubly-fed induction generator (DFIG). The d – q axis equivalent-circuit model under three-phase balanced loading conditions is derived to establish the complete system model including the STG set, the DFIG-based OWF, the series-capacitor compensated line, the UPFC, etc. A damping controller of the proposed UPFC is designed by using pole-assignment approach based on modal control theory to effectively damp out unstable STG modes of the studied system. Both small-signal stability and transient simulation results of the studied system are systematically performed. The simulation results show that the proposed UPFC joined with the designed damping controller can effectively suppress unstable STG modes of the studied power system.

The Small-Signal Stability of Offshore Wind Power Transmission Inspired by Particle Swarm Optimization

Voltage source converter-high-voltage direct current (VSC-HVDC) is the mainstream technology of the offshore wind power transmission, which has been rapidly developed in recent years. The small-signal stability problem is closely related to offshore wind power grid-connected safety, but the present study is relatively small. This paper established a mathematical model of the doubly fed induction generator (DFIG) integrated into the IEEE9 system via VSC-HVDC in detail, and small-signal stability analysis of offshore wind farm (OWF) grid connection is specially studied under different positions and capacities. By selecting two load nodes and two generator nodes in the system for experiments, the optimal location and capacity of offshore wind power connection are obtained by comparing the four schemes. In order to improve the weak damping of the power system, this paper presents a method to determine the parameters of the power system stabilizer (PSS) based on the particle swarm optimization (PSO) algorithm combined with different inertia weight functions. The optimal position of the controller connected to the grid is obtained from the analysis of modal control theory. The results show that, after joining the PSS control, the system damping ratio significantly increases. Finally, the proposed measures are verified by MATLAB/Simulink simulation. The results show that the system oscillation can be significantly reduced by adding PSS, and the small-signal stability of offshore wind power grid connection can be improved.

Modal Control Design of Damping Controllers for Thyristor-Controlled Series Capacitor to Stabilize Common-Mode Torsional Oscillations of a Series-Capacitor Compensated Power System

This paper proposes a unified approach based on modal control theory to design damping controllers of a thyristor-controlled series capacitor (TCSC) for stabilizing the inherent common-mode torsional interactions occurred in a series-capacitor compensated power system. The studied power system includes two nonidentical turbine-generator sets connected to an infinite bus through a common series-capacitor compensated transmission line. The employed TCSC is properly connected in parallel with a part of the series-capacitor bank of the compensated transmission line. The damping controllers of the TCSC employ the speed deviations of both turbine-generator sets as input signals to stabilize unstable torsional modes of the studied system by increasing the damping of these modes. Both frequency-domain approach based on eigenvalue analysis and time-domain scheme based on nonlinear-model simulations under different disturbance conditions are systematically performed. It can be concluded from the simulated results that the employed TCSC joined with the damping controllers designed by using modal control theory can effectively stabilize the common-mode torsional oscillations of the studied series-capacitor compensated system.

Modal Space Feedforward Control for Electro-Hydraulic Parallel Mechanism

As a parallel mechanism with six-degree-of-freedom, an electro-hydraulic shaking table is endowed with strong coupling characteristics among different degree-of-freedoms. When the electro-hydraulic shaking table moves to one direction, there will be some unnecessary related motions in other directions, which will affect the tracking accuracy. The kinematics model, the dynamic model, and the electro-hydraulic model are all established based on analyzing the components and working principles of the electro-hydraulic shaking table. After that, a modal space controller is built on the basis of a three-variable feedback controller by relying on the designed modal space matrix on the premise of modal control theory. In this regard, a multiple-input multiple-output system with strong coupling within the physical space is transformed into a set of single-input single-output systems independent from each other within the modal space. Moreover, the accuracy of vibration control can be improved by introducing a discrete feedforward controller. It is evident from the experimental results that the proposed control strategy can effectively improve the accuracy of vibration control.

Stability Analysis of a Hybrid Multi-Infeed HVdc System Connected Between Two Offshore Wind Farms and Two Power Grids

This paper presents the stability simulation results of two equivalent aggregated offshore wind farms (OWFs) based on doubly-fed induction generator fed to two power grids through a hybrid multi-infeed high voltage dc (HVdc) system. The hybrid multi-infeed HVdc system consists of a line-commutated converter (LCC)-based HVdc link and a voltage-source converter-based HVdc link. A static synchronous compensator (STATCOM) is connected at the rectifier station of the LCC-based HVdc link. A unified approach using a pole-assignment approach based on a modal control theory is employed to design the damping controllers for the two HVdc links, respectively. Steady-state results under different wind speeds of the two OWFs are carried out. Comparative dynamic responses of the studied system with and without the designed damping controllers for the two HVdc links under wind-speed changes are also achieved. Comparative transient simulations of the studied system with and without the STATCOM subject to a three-phase fault are also performed.

A new modified independent modal space control approach toward control of seismic-excited structures

In this paper, a new modified independent modal space control, namely independent modal space proportional-integral-derivative control (IMSPIDC), is proposed. The proposed control approach is developed through combining the well-known idea of proportional- integral- derivative control with the independent modal space control theory. IMSPIDC is applied to the problem of structural control under seismic excitation. A good trade-off between the conflicted modal structural responses and modal control force is crated using a multi-objective cuckoo search. Considering two different control devices includes: (1) an active tuned mass damper and (2) a system of active tendons, the performance of the proposed controller is evaluated in comparison with an independent modal space Linear–quadratic–Gaussian control (IMSLQRC). The Simulation results show that the IMSPIDC performs significantly better than the IMSLQRC in reduction of seismic responses of the structure. The proposed controller has several advantages in terms of simplicity and reduction of required sensors to the number of controlled stories. Furthermore, an evaluation of robustness against stiffness uncertainties indicates that the IMSPIDC gives a better performance than IMSLQRC in this term.

Stability Improvement of a Two-Area Power System Connected With an Integrated Onshore and Offshore Wind Farm Using a STATCOM

This paper presents stability-improvement results of a two-area power system connected with an integrated onshore and offshore wind farm (WF) using a static synchronous compensator (STATCOM). The onshore WF of 19.8 MW is based on dynamic-slip induction generator, while the offshore WF of 100 MW is based on doubly-fed induction generator. The qd axis equivalent-circuit model is derived to establish the complete system model under three-phase balanced conditions. A lead-lag power-oscillation damping controller (PODC) of the STATCOM is designed by using the phase-compensation method based on modal control theory to damp out low-frequency oscillations of the studied two-area power system. A systematic strategy using a frequency-domain approach based on eigenvalue analysis and a time-domain approach based on nonlinear-model simulations is performed to evaluate the effectiveness of the proposed control scheme. It can be concluded from the simulation results that the proposed STATCOM joined with the designed PODC is capable of improving stability of the studied two-area power system connected with the integrated onshore and offshore WF under various disturbance conditions.

可変減衰機構を用いたトラス鉄塔のセミアクティブ制振

1. Introduction Application of energy dissipation devices for the passive vibration control of truss towers has been recently researched, because these towers were generally designed to resist wind load. However, as the earthquake load requirements increases, these towers are possibly to be damaged by large earthquakes. On the other hand, researchers have developed semi-active control device that produces any adjustable control force using variable dampers. This paper describes an investigation of applying semi-active control system to truss towers using variable dampers. First, hysteresis of variable dampers is examined using DDOF system. Second, the semi-active control system is applied to the truss towers to confirm the seismic response reduction compared with the passive vibration control. 2. Overviews of control method and analysis method In this study the Maxwell model is used to exhibit variable dampers. Modal control and optimal control theory are introduced to calculate command forces. For variable dampers, the damping coefficient can be adjusted between upper and lower limits to achieve the command forces. Optimal damping coefficients for passive dampers are applied for the upper limit of variable dampers. 3. Semi-active control of DDOF system The hysteresis curves of variable and passive dampers are compared using DDOF system. The shape of a theoretical hysteresis of semi-active controlled SDOF is a rhombus by adjusting damping coefficients of variable dampers. In DDOF system, when the variable dampers are placed at a location close to free end, or mass at fixed end is larger than that at free end, the shape of hysteresis similar to a butterfly. However, variable dampers can dissipate larger amounts of energy than passive dampers. 4. Semi-active control of truss tower structure A truss tower numerical model is created based on an actual telecommunication truss tower consisting of 15 layers. The damper arrangement of variable dampers is basically defined by the optimal locations of passive dampers. The effects of choosing control mode, damper arrangement, the number of dampers and value of maximum damping coefficient on response reduction effect are discussed using the numerical model. 5. Conclusions As a conclusion, the following results are obtained. 1) In DDOF system, when the variable dampers are placed at a location close to free end, or mass at free end is smaller than that at fixed end, the shape of hysteresis similar to a butterfly. However, variable dampers can dissipate larger amounts of energy than passive dampers. 2) In the case of truss tower, peak displacement of semi-active control is less than passive control by using only 1st mode as the control mode. However, then peak acceleration of semi-active control is higher than that of passive control at lower layers, because of adjusting damping coefficients of variable dampers. 3) When the variable dampers are installed at the optimal locations of passive dampers, the displacement response of the semi-active control is smaller than that of passive control. The effect of semi-active control on the displacement reduction increases, as that of passive control decreases. 4) The effect of semi-active control on response reduction is more significant compared to passive control as the number of dampers decreases. 5) The optimal damping coefficient of passive dampers provides the least displacement response in passive control. On the other hand, for semi-active control, the displacement response becomes smaller as the upper limit of damping coefficient of variable dampers increases.

English

This paper proposes a unified power flow controller (UPFC)-based oscillation damping controller for use with a permanent magnet synchronous generator (PMSG)-based offshore wave farm (OWF). A novel intelligent damping controller (NIDC) was used to increase the stability of power control and improve the performance, where the proposed NIDC consists of the adaptive critic network, the Functional Link based Elman Neural Network (FLENN), and PID linear damping controller. The UPFC is used with the NIDC to OWF, which is connected to a single-machine infinite-bus to improve system stability. The PID damping controller is analysis of complex eigenvalues based on a theory of modal control. The node connecting weights of the FLENN and critic network are trained online. The proposed NIDC can be used to achieve better damping characteristics. The internal power fluctuations in the power system can also be effectively alleviated under variable wind power generation

Integrated Offshore Wind and Seashore Wave Farm Fed to a Power Grid Using a UPFC

This project presents the analyzed results of an integrated offshore wind and seashore wave farm fed to an onshore power grid through a unified power flow controller (UPFC) to simultaneously achieve power-fluctuation mitigation and stability improvement. A damping controller of the proposed UPFC is designed by using modal control theory to render adequate damping characteristics to the studied system. A frequency-domain scheme based on a linear system and a time-domain scheme based on a nonlinear system. From time domain analysis, the UPFC is designed. The proposed UPFC joined with the designed damping controller can effectively stabilize the studied integrated OWF and SWF under various interruption conditions. The fluctuated power injected in to the power grid can also be effectively mitigated by the proposed control scheme.

Modal liquid crystal array of optical elements

In this study, a novel liquid crystal array based on modal control principle is proposed and demonstrated. The advanced device comprises a six striped electrode structure that forms a configurable 2D matrix of optical elements. A simulation program based on the Frank-Oseen equations and modal control theory has been developed to predict the device electrooptic response, that is, voltage distribution, interference pattern and unwrapped phase. A low-power electronics circuit, that generates complex waveforms, has been built for driving the device. A combined variation of the waveform amplitude and phase has provided a high tuning versatility to the device. Thus, the simulations have demonstrated the generation of a liquid crystal prism array with tunable slope. The proposed device has also been configured as an axicon array. Test measurements have allowed us to demonstrate that electrooptic responses, simulated and empirical, are fairly in agreement.

Stability Analysis of an Integrated Offshore Wind and Seashore Wave Farm Fed to a Power Grid Using a Unified Power Flow Controller

This paper presents the analyzed results of an integrated offshore wind and seashore wave farm fed to an onshore power grid through a unified power flow controller (UPFC) to simultaneously achieve power-fluctuation mitigation and stability improvement. The performance of the studied offshore wind farm (OWF) is simulated by an equivalent aggregated 100-MW doubly-fed induction generator (DFIG) while the characteristics of the studied seashore wave farm (SWF) are simulated by an equivalent aggregated 60-MW squirrel-cage induction generator (SCIG). A damping controller of the proposed UPFC is designed by using modal control theory to render adequate damping characteristics to the studied system. A frequency-domain approach based on a linearized system model using eigenvalue analysis and a time-domain scheme based on a nonlinear system model subject to disturbance conditions are systematically carried out. It can be concluded from the simulation results that the proposed UPFC joined with the designed damping controller can effectively stabilize the studied integrated OWF and SWF under various disturbance conditions. The inherent power fluctuations injected to the power grid can also be effectively mitigated by the proposed control scheme.

The Spatial Intelligent Structural Active Control Experimental Research

Active control in the application has more and more research, the independent modal space control method is transform the system equation into modal coordinates, then obtain the internal decoupling equations express by modal coordinates, and based on control algorithm calculate the modal control force, which achieve real-time control effect. The control calculation method is simple and efficient to meet the needs of active control. The paper introduce modal control theory and implement methods, design and manufacture the piezoelectric driving lever based on the working principle of the piezoelectric pile, then through the test, give the voltage-driving force relationship, which is linear. An active control experiment on a three-layer intelligence space structure had been done, it can be seen that through the active control, the corresponding modal displacement and acceleration of the structures control are a lot of inhibition; at the same time, through spectral analysis, it can be seen the structured modal damping coefficient corresponding to varying degrees have been improved.

Stability Analysis of Four PMSG-Based Offshore Wind Farms Fed to an SG-Based Power System Through an LCC-HVDC Link

This paper presents the stability analyzed results of four permanent-magnet synchronous generator (PMSG)-based offshore wind farms fed to an synchronous generator (SG)-based power system through a line-commutated converter (LCC)-based HVDC link. The damping controller of the inverter station of the HVDC link is designed by using modal control theory to contribute adequate damping to the studied SG-based power system under different operating conditions. A frequency-domain scheme based on eigenvalue analysis and a time-domain method based on nonlinear model simulations are both performed to demonstrate the effectiveness of the proposed control scheme. It can be concluded from the simulation results that the proposed LCC-HVDC link combined with the designed damping controller at the inverter station cannot only render adequate damping to the studied SG under various operating conditions but also effectively mitigate inherent SG oscillations under severe disturbance conditions.

Comparative Stability Enhancement of PMSG-Based Offshore Wind Farm Fed to an SG-Based Power System Using an SSSC and an SVeC

This paper presents the comparative results on stability improvement of an offshore wind farm (OWF) fed to a synchronous generator (SG)-based power system using a series static synchronous compensator (SSSC) and a series vectorial compensator (SVeC). The studied OWF with capacity of 80 MW is based on permanent-magnet synchronous generators (PMSGs) with power converters. To clearly compare the damping contributed by the control devices, the damping controllers of the proposed SSSC and SVeC are properly designed by assigning the mechanical mode and exciter mode of the studied SG-based power system on the same locations of the complex plane using modal control theory. Frequency-domain approach based on eigenvalue analysis and time-domain approach based on nonlinear model simulations are systematically performed. It can be concluded from the simulation results that the SVeC can offer better damping characteristics to both mechanical mode and exciter mode of the studied SG-based power system under various operating conditions and different disturbance conditions than the SSSC.

Comparisons of Damping Controllers for Stability Enhancement of an Offshore Wind Farm Fed to an OMIB System Through an LCC-HVDC Link

This paper presents an effective control scheme to simultaneously perform power-fluctuation mitigation and damping improvement of a permanent-magnet synchronous generator (PMSG)-based offshore wind farm (OWF) fed to a one-machine infinite-bus (OMIB) system using a high-voltage direct-current (HVDC) link based on line-commutated converter (LCC). The rectifier current regulator (RCR) and the inverter current regulator (ICR) of the HVDC link are individually designed using modal control theory to render adequate damping to the dominant modes of the synchronous generator (SG) of the studied OMIB system under different operating conditions. A frequency-domain scheme based on eigenvalue analysis and a time-domain method based on nonlinear model simulations are both carried out to compare the damping characteristics of the two damping controllers. It can be concluded from the simulation results that the proposed LCC-HVDC link combined with the designed ICR can render better damping performance to the qualities of the LCC-HVDC and the OWF than the designed RCR.