Generalized Impedance Controller Research Articles

Real-time analysis of voltage and frequency regulation of self-excited induction generator based micro hydro plant using generalized impedance controller

– The self-excited induction generator (SEIG) is well accepted for application in micro hydropower plants. However, in the edge-of-grid application it exhibits a limitation in its capacity to sustain the desired terminal voltage along with the frequency of variations in the prime mover's speed and load. Terminal voltage and frequency regulation are significant concerns for such schemes, and many such techniques are available to regulate the same. This paper presents a closed-loop control technique based on a generalized impedance controller (GIC) responsible for the impedance-controlled functioning of the pulse width variation voltage source converter (PWM-VSC) to regulate frequency and terminal voltage of machine with various loading conditions. A coupling transformer is connected between GIC and SEIG, and the ratings of GIC and transformer should be the same as SEIG, as GIC must compensate for the entire SEIG output. Three phase, 2.2 kW, 415 V, 4.8 A, 50 Hz SEIG, and a three IGBT-based voltage-sourced inverter with coupling transformer, are modelled in MATLAB environment. SEIG frequency and voltage effects in response to the GIC modulation index and phase angle are investigated in the real-time environment using the OPAL-RT (ver. OP4510) environment. The voltage and frequency are controlled using the proposed SEIG-GIC scheme, and the simulation results achieved from MATLAB/Simulink were validated with real-time observations.

Intelligent Impedance Control using Wavelet Neural Network for dynamic contact force tracking in unknown varying environments

In this paper, the Intelligent Impedance Control based Wavelet Neural Network (IIC-WNN) is introduced as a noble adaptive variable impedance approach to enhance the efficiency of tracking the desired force and interaction with varying unknown (in terms of unknown stiffness and unknown geometric) environment. In the proposed method, a systematic online adaptation mechanism using the wavelet neural network is presented to adapt the impedance parameter according to a variable environment. Using the introduced adaptive law, the robot would be able to track the desired force on the moving environment with the unknown stiffness. Unlike the general impedance control which the position and stiffness of the environment need to be available and known for choosing the impedance parameters, the proposed structure for the impedance equation leads to adapt the impedance parameters according to the interaction environment. In addition, the stability conditions and adaptation laws using Lyapunov’s method for the variable impedance are given to guarantee the force tracking and stability of the closed-loop system. Finally, various numerical and experimental results verify the performance of the proposed adaptive approach. The experimental results strongly prove that the presented method has a better force tracking performance than the general impedance with constant parameters.

Modelling and simulation of self-excited induction generator driven by a wind turbine

The excellent specifications of the isolated squirrel cage self-excited induction generator (SEIG) make it the first choice for use with renewable energy sources. However, poor voltage and frequency regulation (under load and speed perturbations) are the main problems with isolated SEIGs. Wide dependence on the SEIG requires prior knowledge of its behaviour with regard to variations in the input of mechanical power and output of electrical power to develop a control system that is capable of maintaining the voltage and frequency at rated values, as far as possible, with any change in the input or output power of the SEIG. In this paper, a mathematical model of a wind energy conversion system (WECS) based on a squirrel cage SEIG with a generalized impedance control (GIC) was built using the Matlab/Simulink environment in a d-q stationary reference frame. A fuzzy logic controller (FLC) was used to control the parameters of the GIC. The training of the FLC was conducted by a neural network through Matlab's Neuro-Fuzzy designer. The results of this paper showed that the trained FLC succeeded in controlling the real and reactive power flow between the SEIG and the GIC system, in which the maximum variation for both magnitude and frequency of the generated voltage with any load or wind speed perturbation will not exceed (0.2 %) for the frequency and (3 %) for the voltage magnitude in both directions. The SEIG model was validated by comparing the results obtained with those of well-known studies with the same rating and operating conditions

Null-space impedance control of 7-degree-of-freedom redundant manipulators based on the arm angles

An impedance control method in null-space for 7-degree-of-freedom redundant manipulators is presented in this article. The null-space impedance motion of the redundant manipulator was described in the angle domain and a null-space impedance equation was established. To successfully obtain joint angular velocity, a high-gain observer is designed. The stability of the proposed control method was proved based on passive theory. The proposed null-space impedance control method not only preserved the Cartesian space impedance characteristics of the redundant manipulator but also achieved null-space impedance control. When the manipulator interacted with the outside world, the position error of the end effector asymptotically converged due to the self-motion of the manipulator. Simulations and experiments of the general impedance control method and the proposed impedance control method verified the effectiveness of the proposed method.

A Novel Speed Adaptive Stator Current Compensator for Voltage and Frequency Control of Standalone SEIG Feeding Three-Phase Four-Wire System

This paper presents the operating principle and performance of a generalized impedance controller (GIC)-based novel speed adaptive stator current compensator for voltage and frequency regulation of self-excited induction generator (SEIG) in standalone system feeding three-phase four-wire (3P4W) loads. The GIC has three one-phase full-bridge voltage source converters in 3P4W configuration with a battery bank at common dc bus. Before installing the SEIG on site, its rotor speed versus stator current characteristics is established by driving SEIG over a range of supersynchronous speeds, while the stator is connected to the ac source of rated voltage and frequency. The key aspect of this method is restoration of SEIG stator current in each phase to the pre-established speed-dependent stator current reference under unbalanced load and source perturbations. This is attained by identifying the modulation index and angle of individual GIC phase voltages using time integrals of active–reactive current amplitude errors of the respective stator phase. When these integrals attain steady value, the SEIG phase currents and voltages get restored, while the GIC operating in grid-forming mode locks the system frequency at a desired value. Integrated system model is simulated in MATLAB/Simulink to study the effects of perturbations on regulating the SEIG stator phase currents, voltages, and frequency. Efficacy of the scheme is validated experimentally by DSP-based implementation of the control algorithm.

An Approach to Improve the Performance of Three-phase Self-excited Induction Generator Feeding an Induction Motor Load using Hilbert Transform and Coordinate Rotation Digital Computer

Self-excited induction generators are mostly preferred in isolated areas to feed three-phase squirrel-cage induction motors for agricultural purposes to pump water. When the induction motor is connected to the self-excited induction generator without any voltage and frequency controller, it causes severe transients in the electrical and mechanical variables of the generator. Due to the large starting current requirement of the induction motor, there is a collapse of the terminal voltage of the generator; thus, the self-excited induction generator requires a voltage and frequency controller to run an induction motor safely in remote and isolated areas. This article presents a voltage and frequency control scheme for the self-excited induction generator to run an induction motor using a generalized impedance controller. The novelty of this work is to estimate the peak terminal voltage and frequency of the self-excited induction generator using Hilbert transform and the Coordinate Rotation Digital Computeralgorithm. The proposed scheme requires only one voltage sensor, and its output voltage is processed to estimate peak voltage and control the modulation index of the generalized impedance controller to control the self-excited induction generator voltage and frequency and run the induction motor without causing any disturbance.

An approach to estimate and control SEIG voltage and frequency using CORDIC algorithm

In wind energy generation, self-excited induction generators (SEIGs) are playing a vital role in isolated areas where the extension of the grid is not feasible. But the major problem with such generators are their inability to maintain the terminal voltage and frequency constant with the load. Many SEIG systems require the computation of peak voltage and frequency for the subsequent feeding to a voltage and frequency controller for processing. In this paper, a new technique for computing the peak voltage of a SEIG using the COordinate Rotation DIgital Computer (CORDIC) algorithm is proposed. The proposed peak voltage estimation scheme requires only one voltage sensor. The SEIG voltage and frequency is controlled using a generalized impedance controller. To validate the simulation results obtained from MATLAB/Simulink, an experiment is also carried out using a TMS320F2812 DSP processor.

Synchronized Operation of DSP-Based Generalized Impedance Controller With Variable-Speed Isolated SEIG for Novel Voltage and Frequency Control

In this paper, the performance of a novel two-loop control strategy for a three-phase self-excited induction generator (SEIG), used in wind/microhydro/biogas-based isolated generation schemes, is presented. The implementation of the grid-interactive synchronization of the generalized impedance controller (GIC), an impedance-controlled operation of pulse width modulation (PWM) voltage-source converter, with SEIG is described. The SEIG frequency is tracked using digital phase-locked loop implemented on a dSpace DSP platform. The open-loop SEIG-GIC system is experimentally analyzed for the sensitivity of the SEIG voltage and frequency to GIC modulation index $m$ and phase angle $\delta$ . Based on this, a simple and practical control strategy with proportional–integral (PI)-based voltage and frequency feedback loops is evolved for the regulation of the SEIG voltage and frequency. A novel design procedure for both the PI controllers for stable closed-loop operation is presented. The performance of the proposed closed-loop system is experimentally tested under speed and load perturbations.

Adaptive Discrete-Time Sliding Mode Impedance Control of a Piezoelectric Microgripper

Delicate interaction control is a crucial issue for automated microsystems dedicated to microobjects handling. This paper proposes a new approach to regulate both position and contact force of a piezoelectric-bimorph microgripper for micromanipulation and microassembly applications. The methodology is developed based on the framework of a discrete-time sliding mode generalized impedance control with adaptive switching gain. One unique feature lies in its easy implementation based on a second-order dynamic model, whereas neither a state observer nor a hysteresis/creep model of the system is required. The stability of the control system is proved in theory, which ensures the tracking performance in the presence of model uncertainties and disturbances. The effectiveness of the scheme is validated by experimental investigations on grasp operation of a microgear. Results show that the approach is capable of accomplishing precision position/force control simultaneously. Moreover, the influences of control gains and target impedance parameters on the tracking performance are addressed, and the achievement of balance between the position and force control accuracy is discussed.

Six-DOF Impedance Control of Dual-Arm Cooperative Manipulators

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, the problem of impedance control of dual-arm cooperative manipulators is studied. A general impedance control scheme is adopted, which encompasses a centralized impedance control strategy, aimed at conferring a compliant behavior at the object level, and a decentralized impedance control, enforced at the end-effector level, aimed at avoiding large internal loading of the object. Remarkably, the mechanical impedance behavior is defined in terms of geometrically consistent stiffness. The overall control scheme is based on a two-loop arrangement, where a simple proportional integral derivative inner motion loop is adopted for each manipulator, while an outer loop, using force and moment measurements at the robots wrists, is aimed at imposing the desired impedance behaviors. The developed control scheme is experimentally tested on a dual-arm setup composed of two 6-DOF industrial manipulators carrying a common object. The experimental investigation concerns the four different controller configurations that can be achieved by activating/deactivating the single impedance controllers. </para>

Voltage and Frequency Control of a Stand Alone Brushless Wind Electric Generation Using Generalized Impedance Controller

In this paper, a new strategy for the control of terminal voltage and frequency of a stand-alone self-excited induction generator-(SEIG) based wind generator, working with variable speed and load is proposed. With a generalized impedance controller (GIC) (voltage source pulsewidth-modulated inverter with a dc-link battery), a new strategy to maintain the active and reactive power balance at the SEIG terminals has been introduced to control its terminal voltage and frequency. In the proposed control strategy, only a voltage feedback loop has been used to control both the SEIG terminal voltage and the frequency. A mathematical model of the SEIG-GIC system under wind generator environment has been developed and simulated in the MATLAB/Simulink. The simulation results are validated with the experimental ones conducted on a laboratory prototype of the SEIG-GIC system. The novelty of the present technique is that the GIC is capable of maintaining a constant SEIG terminal voltage and frequency, following both speed and load perturbations, with only a single (voltage) feedback loop.

Analysis of Operation of a Self-Excited Induction Generator With Generalized Impedance Controller

In this paper, analysis of the operation of a stand-alone self-excited induction generator (SEIG) with generalized impedance controller (GIC) (voltage source pulsewidth-modulated bidirectional inverter with dc link battery) has been discussed. Model of the SEIG along with the generalized impedance controller, has been developed in MATLAB/Simulink environment. The simulation results obtained for steady-state operation of the system, following speed and load perturbations have been presented here. The simulation results are validated with the experimental ones, which are conducted on a laboratory prototype of the SEIG-GIC system. The generalized impedance controller is found to be capable of maintaining the frequency of the SEIG constant under open-loop condition, following the speed and load perturbations.

Experimental Implementation of Impedance Based Control Schemes for Assembly Task

Compliant manipulation tasks require the robot to follow a motion trajectory and to exert a force profile while making compliant contact with a dynamic environment. For this purpose, a generalized impedance in the task space is introduced such that the desired motion and the desired interaction force can be commanded and controlled simultaneously. Several control schemes which place different emphases on motion control or force control can be derived from the generalized impedance. The impedance-based control schemes are implemented and the performance evaluated on a common test-bed which involves the insertion of a printed circuit board into an edge connector socket. Experimental results demonstrate the superior motion and force tracking ability of the generalized impedance control method. Furthermore, safe task execution can be achieved in the presence of abnormal operating situation.

A Concept of an Intelligent Fuzzy Control for Assembly Robot

Active accommodation of robotic manipulator in assembly applications is considered. Mechanical impedance control concept has been chosen for development an intelligent controller for assembly robots, where target impedance appears as a control variable. Basic assumption for successful part mating process according to part mating theory is mechanical isotropy of support system. Consequently, target impedance should be adopted as isotropic. The main problem appearing here is complex analytical formulation of isotropic target impedance and uncertainty of parameters related to the robot and environment model. To overcome this problem an adaptive fuzzy model of isotropic target impedance is proposed. The fuzzy model is incorporated into general impedance control law form, to obtain new fuzzy-impedance control law. Proposed control law has been verified by computer simulation.

外乱オブザーバを用いた空気圧ロボットのインピーダンス制御

In order to make a robot perform a contact task with an environment, robot must have an enough skillfulness and compliance simultaneously.Parallel manipulator has attracted an interest because of its features such as a multiple d.o.f. for its compact mechanism which is available for complicated tasks. In the meanwhile pneumatic actuator has a high power/weight ratio and an inherent compliance function due to the air compressibility which makes it possible to perform a minute force regulation. In this paper we apply an impedance control to the prototype of parallel manipulator driven by pneumatic cylinders and its control performances are investigated.There are 2 general impedance control strategies, one is force based type and the other is position based one. In the former one the influence of manipulator's dynamics such as inertia force and damping one affect on the control variable directly, while in the latter one applied external force works as a disturbance. Therefore we construct both types of control system based on the pressure control system to kill out the influence of these disturbances which are estimated with a dimension of a pressure by using a disturbance observer. Moreover we comprise an simplified position based impedance control system. The control performances are compared among the proposed three control systems analytically and the validity of them are proved by some experiments.

Generalized impedance control of robot for assembly tasks requiring compliant manipulation

To perform assembly tasks requiring compliant manipulation, the robot must follow a motion trajectory and exert an appropriate force profile while making compliant contact with a dynamic environment. For this purpose, a generalized impedance in the task space consisting of a second-order function relating the motion errors and interaction force errors is introduced such that the contact force can be commanded and controlled. With generalized impedance control, the robot can behave with a desired dynamic characteristic when it interacts with the environment. To ensure the success of the assembly, a strategy during task planning which takes into consideration the interrelation between motion and force trajectories as well as contact compliance is introduced. The generalized impedance control method is applied to the prismatic joint of a selective compliance assembly robot arm (SCARA) robot for inserting a printed circuit board (PCB) into an edge connector socket. Depending on the progress of the parts joining operation, various amount of interaction forces are generated which have to be accommodated. It is demonstrated that an assembly strategy which consists of a sequence of carefully planned target impedance can enable the task to be executed in a desirable manner. The effectiveness of this approach is illustrated through experiments by comparing the results with those obtained using a well-established position control scheme as well as the original impedance control method.

Modeling, design, and evaluation of advanced teleoperator control systems with short time delay

A real-time teleoperator control system designed to achieve desired performance and robustness under shared compliance control and short time delays of up to a few seconds is evaluated. In the design, telemonitoring force feedback is introduced as a new form of kinesthetic coupling; dynamic characteristics of the master and slave arms are actively modified based on generalized impedance control according to local design criteria; the human dynamics involved in generating a control command based on visual and force stimuli are incorporated into the controller design; and to balance the robustness/performance trade-off, system performance is optimized subject to a known maximum time delay. Simulation results suggest that the system is superior to conventional systems in terms of performance and robustness under short time delays and human control errors. Experimental evidence is presented to supports the advantages of the proposed telemonitoring force feedback. An experimental method for further validating the human dynamic model is described. >