Control using joint torque sensor of robot arm with two‐inertia resonance: Comparison with control using state‐estimation observer

Most industrial robots are driven through reduction gears such as Harmonic Drives and RV gears. Due to the flexibility of the drive system, vibratory behavior occurs during operation. When flexibility is considered, the drive system of the robot joint can be modeled as a resonant mechanical system called a two‐inertia system. Conventionally, studies of two‐inertia system have discussed semiclosed‐loop control using only motor information and a state observer. On the other hand, joint torque sensing of robots has been studied in the harmonic drives that are widely used in robot joints. The joint torque sensor is becoming available with higher performance. In this paper, we consider the control of a robot arm having two‐inertia resonance by using the joint torque sensor. The performance of the torque sensor and that of the observer are compared. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(2): 75–84, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20226     

Implementation of vibration suppression control on FWL processor

In motion or process control systems, a variety of design techniques have been proposed because of the demand for high performance. The higher performance we demand, the higher the degree of the controller becomes. The controller is generally designed by a CAD system and implemented with a microprocessor. But the microprocessor does not have enough precision to realize the results of design by the CAD system. Therefore, the system performance is degraded by finite word length (FWL) effects. To deal with FWL problems, many design methods have been considered in the signal processing field, and high‐ordered digital filters are often used. Among these methods, the implementation technique based on the state‐space realization can minimize the sensitivity to perturbation of coefficients. Noting that optimal realizations with the same transfer function are unique only up to an orthogonal similarity transformation, we must choose the realization within this class of optimal realizations. In this paper, we present an algorithm to find a state‐space realization which minimizes the frequency‐weighted sensitivity measure of the controller performance. Furthermore, we present some experimental results to verify the effectiveness of the proposed algorithm. © 1999 Scripta Technica, Electr Eng Jpn, 128(1): 45–52, 1999     

Short‐span seeking control of hard disk drive with vibration suppression PTC

In a short‐span seeking‐mode of hard disk drives, the resonance modes are getting crucial obstruction to meet the demand on high‐speed data access. In this paper, a novel vibration suppression perfect tracking control (PTC) method is proposed based on controllable canonical realization. In the proposed method, it is assumed that the plant is modeled as the rigid and primary resonance mode. By using this model, the feed forward controller is designed with PTC by multirate sampling control in order to suppress the primary vibration. Additionally, the higher‐order resonance vibration is attenuated by using the trajectory MHVT. The proposed method achieved 16% faster seeking than MPVT, a conventional method. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(1): 66–72, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20546     

Adaptive robust boundary control of coupled bending‐torsional vibration of beams with only one axis of symmetry

In control design for vibration of beams in literature, the beam section is considered to have two axes of symmetry so that the bending and torsional vibrations are uncoupled; thus, the bending vibration is controlled independently without twisting the beam. However, if the cross section of a beam has only one axis of symmetry, the bending and torsional vibrations become coupled and the beam will undergo twisting in addition to bending. This paper addresses Lyapunov‐based boundary control of coupled bending‐torsional vibration of beams with only one axis of symmetry. The control strategy is based on applying a transverse force and a torque at the free end of the beam. The control design is directly based on the system partial differential equations (PDEs) so that spillover instabilities that are a result of model truncation are avoided. Three cases are investigated. Firstly, it is shown that when exogenous disturbances do not affect the beam, a linear boundary control law can exponentially stabilize the coupled bending‐torsional vibration. Secondly, a nonlinear robust boundary control is established that exponentially stabilizes the beam in the presence of boundary and spatially distributed disturbances. Thirdly, to rule out the need for prior knowledge of disturbances upper‐bound, the proposed robust control is redesigned to achieve an adaptive robust control that stabilizes the beam in the presence of disturbances with unknown upper‐bound. The efficacy of the proposed controls is illustrated by simulation results. Copyright © 2016 John Wiley & Sons, Ltd.     

Hamilton‐based adaptive robust control for the speed and tension system of reversible cold strip rolling mill

The adaptive robust control problem for the speed and tension system of reversible cold strip rolling mill is studied based on the Hamilton theory in this paper. First, the dissipative Hamilton model of the rolling mill system's speed and tension outside loop is built through pre‐feedback control, and then, dissipative Hamilton controllers are designed by utilizing the interconnection and damping assignment and the energy shaping method. Second, in order to realize tensiometer‐free control and adaptive robust control for the perturbation parameters and load disturbance, full‐order state observers and adaptive robust controllers are designed for the rolling mill system's speed and tension outside loop by using the “extended system + feedback” method. Third, robust controllers for the rolling mill system's current inside loop are designed based on the cascade control thought, so as to realize the tracking control for the speed and tension of reversible cold strip rolling mill. Theoretical analyses show that the resulting closed‐loop system is stable. Finally, simulation research is carried out on the speed and tension system of a 1422‐mm reversible cold strip rolling mill, and simulation results verify the validity of the proposed control strategy in comparison with the decentralized overlapping control strategy.     

High response torque control of IPMSM using state feedback control based on n‐t coordinate system

This paper proposes a torque control method for interior permanent magnet synchronous motors (IPMSMs). The proposed method uses state feedback control based on a new n‐t coordinate system and controls the voltage amplitude and phase based on the coordinate system. The t‐axis is a tangent line of the constant voltage ellipse, and the n‐axis is a normal line of the ellipse. The n‐axis current is utilized to place the poles of the transfer function at the desired position and reduce the mutual coupling between the voltage amplitude controller and phase controller. The proposed method realizes a high torque response even under parameter variation for the linear range and over‐modulation range of the inverter, including a 6‐step mode. The effectiveness of the proposed method was verified by simulation and experimental results.     

High‐performance V/f control of PMSM using state feedback control based on n–t coordinate system

This paper proposes a new V/f control method for permanent magnetic synchronous motors (PMSMs) without a position sensor. The proposed method uses state feedback control based on an n–t coordinate system, and controls rotational speed and the voltage amplitude. The t‐axis is a tangent line of a constant voltage ellipse, and the n‐axis is a normal line of the ellipse. The t‐axis current is utilized to place the poles of the transfer function at the desired position at low‐speed and high‐speed conditions. The effectiveness of the proposed method was verified by simulation and experimental results.     

Steady‐state stability of shaft torsional oscillation in an ac‐dc interconnected system with self‐commutated converters

Recent progress in power electronics technology makes it possible to consider applying self‐commutated converters using gate turn‐off thyristors (GTOs) to HVDC transmission systems. Since the self‐commutated converter can be operated stably without depending on ac‐side voltage, the magnitude and the phase angle of the converter output voltage can be controlled independently. Therefore, this type of converter will improve voltage stability at its ac side. On the other hand, shaft torsional oscillation of a thermal power plant caused by the interaction between the shaft‐generator system and the control system of the self‐commutated converter is still an open problem. In this paper, a linearized model for eigenvalue analysis of a power system, including HVDC interconnection with self‐commutated converters, is described to analyze the effect of the self‐commutated converter on the shaft torsional oscillation of a thermal power plant. Then, numerical results from the eigenvalue analysis of the shaft torsional oscillation are presented. Results obtained by the frequency response method are also reported. The numerical results make it clear that parameter regions of DC‐AVR and ACR control systems of self‐commutated converters exist where the shaft torsional oscillation may be caused. © 1999 Scripta Technica, Electr Eng Jpn, 128(4): 25–37, 1999     

An anti‐windup strategy for a feedback control system based on youla parametrization

In this paper, the design strategy of anti‐windup controller (AWC) for feedback control system is proposed. The proposed method is based on Youla parametrization of linear controllers in the framework of left coprime factorization. Conventional anti‐windup controllers have difficulty in optimization of parameters. The suppression effect of windup phenomena can be adjusted easily with the proposed AWC. The effectiveness of proposed method is shown with some numerical and experimental results. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 139(4): 64–70, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10013     

Optimal model‐free control for a generic MIMO nonlinear system with application to autonomous mobile robots

In this paper, the design procedure for optimal model‐free control algorithm is presented for the tracking problem of completely unknown nonlinear dynamic systems operating under unknown disturbances. The procedure includes a new structure in the context of model‐free control and data‐driven control algorithms. In the new structure, the unknown nonlinear functions are segmented into 1 unknown linear‐in‐states part and another unknown nonlinear part. The adaptive laws proposed for estimating the unknown system dynamics are regressor‐free estimation methods in which there is no need for regressor parameters and, consequently, the persistent excitation condition is not required anymore. Moreover, the main controller gains are updated online, incorporating the adapted values of linear terms in the system dynamics. A comparative study is presented to show that the proposed optimal model‐free control outperforms the state‐of‐the‐art model‐free control algorithms. In addition, the simulation results for the application of the algorithm on autonomous mobile robots are provided.     

New sensorless vector control methods based on a new minimum‐order flux state observer in the “D‐module” for permanent magnet synchronous motors

This paper proposes new sensorless vector control methods that can be applied to both salient‐pole and non‐salient‐pole permanent magnet synchronous motors (PMSM). The proposed method estimates the phase of rotor flux by the “D‐module observer,” which is newly developed for sensorless vector controls of PMSM. The “D‐module observer” has the following attractive features. (1) It is a new state observer requiring no additional approximation to the motor mathematical model. (2) It is a minimum‐order state observer. (3) Observer gain guaranteeing proper estimation in a wide operating range except for singular zero‐speed can be a simple constant, and can be easily designed. (4) It utilizes motor parameters in the simplest manner. (5) Its structure is very simple and is realized at the minimum computing cost. (6) It can be applied to both salient‐pole and non‐salient‐pole PMSM. (7) It can be realized in both rotor and stator reference frames. Detailed designs and analyses for the “D‐module observer” and “D‐module observer”‐based sensorless vector control systems in both rotor and stator reference frames are given. Their validity and usefulness are examined and confirmed through extensive experiments. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(2): 46–62, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20046     

A design method of a generalized predictive control system based on parametrization of two‐degree‐of‐freedom integral controllers

A new design method for a generalized predictive control (GPC) system based on parametrization of two‐degree‐of‐freedom integral controllers has been proposed. The objective is to guarantee stability of the control system without depending on the design parameters and to achieve low sensitivity against the plant perturbation and the disturbance. The design procedure consists of two steps. First, we design a basic integral controller for a nominal plant using the linear quadratic Gaussian (LQG) method and parametrize a class of two‐degree‐of‐freedom stabilizing controllers. Next, we tune the feedforward controller to incorporate the GPC method into our control structure. A numerical example is presented to show the effectiveness of the proposed method by comparing it with the conventional GPC method. © 1999 Scripta Technica, Electr Eng Jpn, 129(2): 62–70, 1999     

A three‐phase hybrid stepping motor drive system combined with position‐sensorless closed‐loop control

This paper proposes a drive system for a three‐phase hybrid stepping motor, combining sensorless closed‐loop control with conventional open‐loop control. It is characterized by sophisticated control providing both prevention of pulling out from synchronism and suppression of natural rotor oscillation, without any position sensor attached to the motor shaft. A switching technique in chopper control which can enlarge the speed range controllable in the sensorless closed‐loop control is described. Starting and stopping sequences are developed to reduce mechanical natural oscillation produced in the transient state. Finally, the proposed drive system is compared experimentally with a conventional constant‐current open‐loop drive system. It is shown that the proposed drive system can perform the switchover from starting to sensorless closed‐loop operation within 20 ms, and can reduce the natural oscillation caused just after positioning. © 2000 Scripta Technica, Electr Eng Jpn, 131(3): 80–90, 2000     

带零动量轮航天器的逆系统方法姿态控制

为满足带零动量轮航天器姿态响应的快速性与准确性,将航天器姿态模型和飞轮机构及其补偿器视为广义控制对象,采用广义逆系统方法与内模原理相结合设计了复合控制器。在分析动量轮的摩擦阻力效应基础上,设计了基于飞轮非线性观测器的低、高速补偿器,在改变航天器惯量与加入干扰的情况下,通过仿真分析了复合控制的鲁棒性。逆系统实现了广义控制对象的解耦,内模闭环控制器弥补了解耦的非理想性,补偿器加快了姿态响应速度。仿真结果表明,逆系统与内模控制组成的复合控制器对带零动量轮航天器姿态控制是有效的,并且该控制器对航天器惯量参数和干扰具有较强的鲁棒性。     

Model reference adaptive control system design for linear time‐varying systems with unstructured and bounded varying functions

In recent years, many methods of model reference adaptive control system (MRACS) for a linear time‐varying (LTV) plant have been proposed. These methods assumed that the structure of plant parameters is known in advance. However, it is difficult to get a priori information of plant parameters. In this paper, an MRACS design for an LTV system based on high‐order estimator (HOE) is proposed. By applying dynamic certainty equivalence (DyCE) to LTV plants, a new MRAC law of LTV system is derived without knowing the structure of the plant parameters. The MRACS law is generated by using high‐order derivatives of an estimated parameter, so that robust HOE with a normalization signal and σ modification for the system introduced. Our proposed method can attain better performance than conventional methods, such as estimation with variable forgetting factor (VF) and the gradient projection method (GPM). The robust HOE establishes the boundedness of all of the estimated parameters under the condition that the estimated parameter and the first derivative of the parameter are bounded. It is shown that all signals in the adaptive loop are bounded and the output error converges to a closed set. The proposed method is compared to the familiar schemes, the gradient projection method and the estimation based on forgetting factor through numerical simulations, and the effectiveness of our proposed method is shown. © 2000 Scripta Technica, Electr Eng Jpn, 130(4): 87–98, 2000     

Maximum power tracking control for a wind energy conversion system based on a quasi‐ARX neural network model

By itself, a wind turbine is already a fairly complex system with highly nonlinear dynamics. Changes in wind speed can affect the dynamic parameters of wind turbines, thus rendering the parameters uncertain. However, we can identify the dynamics of the wind energy conversion system (WECS) online by a quasi‐ARX neural network (QARXNN) model. A QARXNN presents a problem in searching for the coefficients of the regression vector (input vector). A multilayer perceptron neural network (MLPNN) is an embedded system that provides the unknown parameters used to parameterize the input vector. Fascinatingly, the coefficients of the input vector from prediction model can be set as controller parameters directly. The stability of the closed‐loop controller is guaranteed by the switching of the linear and nonlinear parts of the parameters. The dynamic of WECS is derived with given parameters, and then a wind speed signal created by a random model is fed to the system causing uncertainty parameters and reducing the power that can be absorbed from wind. By using a minimum variance controller, the maximum power is tracked from WECS. From the simulation results, it is observed that the proposed controller is effective in tracking the maximum power of WECS. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Matching a system behavior with a known set of models: A quadratic optimization‐based adaptive solution

The matching process between a time‐domain external behavior of a lumped single‐input single‐output dynamical system and a known set of linear continuous time‐invariant models is tackled in this paper. The proposed online solution is based on an adaptive structure detector, which in finite time locates in the known set of models the one corresponding to the observed external behavior; the detector results from the solution of a constrained quadratic optimization problem. The problem is expressed in terms of the time‐domain activity of a family of discriminating filters and is solved via a normalized gradient algorithm, which avoids mismatching due to the presence of structural zeros in the filters and can take into account band‐limited high‐frequency measurement noise. A failure detection problem concerning a simulated servomechanism is included in order to illustrate the proposed solution. Copyright © 2008 John Wiley & Sons, Ltd.     

A new control strategy with fault ride‐through capability for VSC‐based offshore high power oil pump motor power supply system

In offshore oil platforms, high voltage and power motors (HV motors) are needed when transporting oil to the land. Traditional platform diesel generators cannot support so much power, so the required system must be supplied by the onshore AC grid. In general, when there is a long distance between the offshore platform and the shore, a DC transmission system is more efficient. This paper proposes a power supply approach for these motors using a voltage source converter (VSC) and derives the mathematical model for it. This method combines motor drive theory and studies in DC transmission field. Compared with the traditional motor control, this method, which makes full use of the advantages of VSC, can simplify the control strategy. And by using the Q–U droop characteristic, the strategy improves the system stability and fault ride‐through capability. Simulation is carried out in PSCAD/EMTDC, and the results verify the validity of the control method. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.