In-Joong Ha

Control of induction motors for both high dynamic performance and high power efficiency

The authors attempt to control induction motors with maximum power efficiency as well as high dynamic performance by means of decoupling of motor speed (or motor torque) and rotor flux. For maximum power efficiency, the squared rotor flux is adjusted according to a minimum power search algorithm until the measured power input reaches the minimum. Since the motor speed is dynamically decoupled from the rotor flux, this can be done successfully without any degradation of motor speed responses. The controller depends on rotor resistance but not on stator resistance. However, the performance of the control scheme is robust with respect to variations in rotor resistance because an identification algorithm for rotor resistance is employed. The identification algorithm for rotor resistance has some advantages over the previous methods. To demonstrate the practical significance of the results, some experimental results are presented. >

A Lyapunov-like approach to performance analysis of 3-dimensional pure PNG laws

The 3-dimensional PPNG (pure proportional navigation guidance) law was proposed about forty years ago, but its performance has been analyzed only on the basis of the linearized trajectory equations, which are valid locally around the collision course. We take into full account the nonlinear dynamic characteristics of pursuit situation in the 3-dimensional space to analyze the performance of the 3-dimensional PPNG law more rigorously. We prove that a missile guided by the 3-dimensional PPNG law can always intercept a target maneuvering randomly in the 3-dimensional space if 1) the target acceleration varies with a known bound, 2) the navigation constant is selected large, and either 3a) the initial heading error is small or 3b) the missile keeps the head toward the target during flight. We also propose a modified PNG law, which seems to exhibit better performance at the final phase of pursuit than the conventional PPNG law. We introduce a Lyapunov-like method that proves to be a very powerful tool in obtaining our results. >

Performance analysis of PNG laws for randomly maneuvering targets

The performance of the conventional proportional navigation guidance (PNG) law for a randomly maneuvering target is considered. By means of the Lyapunov method, it is proved that an ideal missile guided by the conventional PNG law can always intercept a target which maneuvers with time-varying normal acceleration provided that the navigation constant is sufficiently large. The authors also propose a modified PNG (MPNG) law which seems to improve the performance of the conventional PNG law at the final phase of pursuit. Simulation results demonstrate that the MPNG law demands less missile acceleration at the final phase of pursuit than the conventional PNG law. >

Design of a CLOS guidance law via feedback linearization

An application of the feedback linearization technique to the design of a new command to line-of-sight (CLOS) guidance law for short-range surface-to-air missiles is described. The key idea lies in converting the three-dimensional CLOS guidance problem to the tracking problem of a time-varying nonlinear system. The result may shed new light on the role of the feedforward acceleration terms used in the conventional CLOS guidance laws. Through computer simulation, the effect of the dynamics of the ground tracker and the autopilot on the guidance performance of the new CLOS guidance law is investigated. >

A resolver-to-digital conversion method for fast tracking

A resolver-to-digital (R/D) conversion method in which a bang-bang type phase comparator is used for fast tracking is proposed. The low-pass filter needed to reject carrier signal and noise is eliminated from the R/D conversion loop. Instead, two prefilters outside the R/D conversion loop take the role of the low-pass filter, resulting in a fast and accurate tracking R/D converter. Some simulation and experimental results and a mathematical performance analysis are presented to demonstrate the superior tracking performance. >

An online identification method for both stator-and rotor resistances of induction motors without rotational transducers

This paper describes an effective online method for identifying both stator and rotor resistances, which is useful in robust speed control of induction motors without rotational transducers. The identification method for stator resistance is derived from the steady-state equations of induction motor dynamics. On the other hand, the identification method for rotor resistance is based on the linearly perturbed equations of induction motor dynamics about the operating point. The identification method for both stator and rotor resistances uses only the information of stator currents and voltages. It can provide fairly good identification accuracy regardless of load conditions and be easily incorporated into any sensorless speed controller proposed in the prior literature. Some experimental results are presented to demonstrate the practical use of the identification method. A sensorless speed control system has been built for experimental work, in which all algorithms for identification and control are implemented on a digital signal processor. The experimental results confirm that the proposed method allows for high-precision speed control of commercially available induction motors without rotational transducers.

An on-line identification method for both stator and rotor resistances of induction motors without rotational transducers

In this paper, the authors propose an effective method of identifying, online, both stator and rotor resistances, which are useful in the speed control of induction motors without rotational transducers, a scheme which is robust with respect to variations in motor parameters. Their identification method for both stator and rotor resistances uses only information of stator currents and voltages. It can provide fairly good identification accuracy regardless of load conditions. Some experimental results are presented to demonstrate the practical use of this identification method.

Iterative identification of state-dependent disturbance torque for high-precision velocity control of servo motors

We present a computationally very efficient learning control method which is ideally tailored to high-precision velocity control of servo motors in the presence of the disturbance torque which is unknown, unstructured, and state-dependent. The proposed learning control method can drive the steady state velocity error to zero and, furthermore, can be used to identify the unknown disturbance torque in look-up table form. In order to demonstrate the generality and practical use of our work, we present the rigorous convergence analysis of the learning control algorithm and some experimental results using a single degree-of-freedom manipulator.

Novel Position-Based Visual Servoing Approach to Robust Global Stability Under Field-of-View Constraint

In this paper, we shed new light on position-based visual servoing (VS) by introducing the concept of a 3-D visible set for position-based VS (PBVS), which can serve to play exactly the role of the 2-D visible set, the image plane, for image-based VS. Our 3-D visible set is convex even in the presence of uncertainties in intrinsic and extrinsic parameters of the camera, just as the image plane. Then, we can ensure the field of view (FOV) constraint simply by controlling the camera pose to follow a smooth straight-line trajectory in our 3-D visible set for PBVS, which simply connects two points determined by the initial and desired poses of the camera. In fact, this is, to our best knowledge, the first result in PBVS that has guaranteed theoretically robust global stability under the FOV constraint with respect to uncertainties in intrinsic and extrinsic parameters of the camera as well as in the distance between the camera and the object at the desired pose. Furthermore, our PBVS scheme is computationally simple compared to the prior works. To demonstrate further the validity and practicality of our PBVS scheme, we also present various experimental results using a six-degree-of-freedom robotic manipulator.

A state-space approach to analysis of almost periodic nonlinear systems with sector nonlinearities

The nonlinear system considered in this paper consists of two components-a linear system and a time-varying nonlinear element in the feedback connection-and is almost periodic. It is shown using a state-space approach (or Lyapunov approach) that if the well-known circle criterion is satisfied, then there exists an almost periodic solution which is uniformly asymptotically stable in the large. Furthermore, it is also shown that the spectra of the almost periodic solution can be characterized by those of the input and the time-varying nonlinearity.