Eduardo Liceaga-Castro

Speed and Position Controllers Using Indirect Field-Oriented Control: A Classical Control Approach

Torque control for induction motors under the scheme of indirect field-oriented control (IFOC) considering rotor resistance perturbations is analyzed via linear approximations. Several important characteristics of IFOC are elucidated, leading to the design of linear, robust, and performance-based torque, speed, and position controllers. In particular, the resulting controllers are of a low order, robust to rotor resistance perturbations, and are designed according to classical performance specifications, which is a combination of characteristics that have been historically difficult to achieve. General control design guidelines valid for any induction motor are presented. In addition, the stability and minimum phase conditions of the IFOC torque controller are fully derived for any induction motor. These conditions are of prime importance when designing fixed linear speed or position controllers. A case study for a typical motor, including the design of a series of robust controllers and real-time experimental results, is presented. The proposed approach makes use of well-known classical control methods that allow the results presented here to be further extended using any linear single-input-single-output controller design tool, such as H∞ and quantitative feedback theory.

Beyond the Existence of Diagonal Controllers: from the Relative Gain Array to the Multivariable Structure Function

A study related to coupling measurement and the existence of diagonal controllers for multivariable linear systems is presented. It is shown that the relative gain array (RGA) can be expressed in terms of the multivariable structure function (MSF). Moreover, the appropriate interpretation and handling of the MSF allows: (a) to establish the dynamical structure of the multivariable control system, (b) to prove the existence of stabilising diagonal controllers, (c) to determine whether design specifications can be met, and (d) the general coupling measurement among channels. In order to show the application of the MSF to the analysis and design of diagonal controllers, a family of plants is studied, ranging from non coupled minimum-phase to highly coupled and non-minimum phase plants. The actual multivariable control designs are included for completeness. The examples here presented may be a good benchmark for further analysis and comparisons.

Fundamental Analysis of the Electromechanical Oscillation Damping Control Loop of the Static VAr Compensator Using Individual Channel Analysis and Design

This paper presents the first individual channel analysis and design (ICAD) of a high-order synchronous generator and a static VAr compensator (SVC) featuring a damping control loop. Particular emphasis is given to the closed-loop performance and robustness assessments. Fundamental analyses are carried out using ICAD and its frequency-domain approach to explain the dynamic behavior of the generator affected by an SVC with damping capabilities. A coordinated SVC voltage and damping control is achieved in a straightforward fashion owing to the transparent manner in which ICAD treats the complex interactions taking place between the synchronous generator and the SVC with a damping control loop. Using the ICAD framework, an indepth comparison is made between the competing abilities to provide system damping of the SVC and the power system stabilizer.

2x2 Individual Channel Design MATLAB ® Toolbox

In this paper a novel software for analysis and design of multivariable 2x2 control systems is presented. The 2x2 Individual Channel Design MATLAB®Toolbox is a valuable aid for analysing and designing multivariable control systems under the framework of the Multivariable Structure Function (MSF) and Individual Channel Design (ICD). Given a set of specifications for a 2-input 2-output multivariable control system the appropriate use of the toolbox can lead to successful and robust controllers. The process is based on an iterative procedure. Closed loop simulations (in SIMULINK®) are included so results can be tested. Final stability margins and robustness measures are also assessed. A design example is included for completeness. The development of the general m x m case is in progress.

An Efficient Controller for SV-PWM VSI Based on the Multivariable Structure Function

In this paper a novel control strategy for pulse-widh modulated voltage source inverters (PWM VSI) is presented. It is based on a linear, diagonal, low order, minimum-phase, fixed, and stable multivariable controller. It is obtained via individual channel design (ICD), a new framework that allows analysis and synthesis of multivariable control systems by means of the multivariable structure function (MSF). Such controller generates the appropriate reference voltage signals for the power inverter via a space-vector PWM (SV-PWM), which in turn provides the voltage signals for the terminals of an induction motor. The theoretical principles behind this control strategy are summarised for completeness. The similarities and differences between some current loop controllers found in literature and the scheme here proposed are discussed. In order to show the ICD controller performance a digital simulation is included. Moreover, it is also shown through the MSF that the dynamical system structure is not sensible to rotor speed or parameter variations. Therefore, it is possible to design a fixed linear robust controller for the whole speed range. Such solution is feasible for engineering applications due to its simplicity and robustness.

Induction Motor Control: Multivariable Analysis and Effective Decentralized Control of Stator Currents for High-Performance Applications

The adequate control of stator currents is a fundamental requirement for several high-performance induction motor (IM) control schemes. In this context, classical linear controllers remain widely employed due to their simplicity and success in industrial applications. However, the models and methods commonly used for control design lack valuable information, which is fundamental to guarantee robustness and high performance. Following this line, the design and existence of linear fixed controllers is examined using individual channel analysis and design. The studies presented here aim to establish guidelines for the design of simple (time invariant, low order, stable, minimum phase, and decentralized) yet robust and high-performance linear controllers. Such characteristics ease the implementation task and are well suited for engineering applications, making the resulting controllers a good alternative for the stator current control required for high-performance IM schemes such as field-oriented, passivity-based, and intelligent control. Illustrative examples are presented to demonstrate the analysis and controller design of an IM, with results validated in a real-time experimental platform. It is shown that it is possible to completely decouple the stator current subsystem without the use of additional decoupling elements.

Induction motor current controller for Field Oriented Control using Individual Channel Design

A control strategy for the design of an induction motor stator-current controller is presented. The strategy is based on a controller, which is linear, diagonal, low order, stable, minimum-phase and time-invariant. Moreover, high frequency modes are avoided. It is shown that the design of high performance multivariable controllers, with such characteristics, can be obtained under the framework known as individual channel analysis and design. The multivariable structure function plays a crucial role under this framework. It is thanks to this function that it is possible to conclude that the dynamical system structure is not affected by the rotor speed or typical parameters variations. Therefore, it is possible to achieve uniform performance for the whole speed range of the motor with a fixed linear controller. In addition a proportional indirect field oriented control speed controller is implemented. The control scheme has been proven with real time experiments, showing that the solution proposed is well suited for engineering applications thanks to its simplicity, robustness and excellent performance.

Analysis and efficient control design for generator-side converters of PMSG-based wind and tidal stream turbines

Mitigation of climate change has stimulated an increased penetration of renewable generation into electricity grids. A substantial amount of the future energy mix is projected to come from renewable sources such as offshore wind, but marine energy may be an important contributor due to the great potential of wave and tidal stream generation. Wind and tidal stream turbines feature similarities: electric machines used, system configuration and control schemes-aiming to extract maximum power from the wind or flow. In this line, individual channel analysis and design (ICAD), a frequency domain framework with the help of which the investigation of the potential and limitations for control design of multivariable systems can be assessed, is employed for turbines based on permanent magnet synchronous generators. Through ICAD, a formal evaluation of the internal coupling of the turbine generator is performed. Results offer formal insight into control strategies based on vector control - with emphasis made on the generator-side of the full power converter. The analysis shows that the use of decoupling loops is not necessary to ensure a satisfactory performance. This is further examined through a simulation carried out in MATLAB/Simulink, showing the effectiveness of the approach.

Simplifying quadrotor controllers by using simplified design models

A series of design models for the quad-rotor vehicle (QRV) are presented. These design models include a full nonlinear model which contains the most relevant dynamics. This model uses a traditional aeronautical structure. This structure may not be the best for typical nonlinear control design, but it is useful for simulation and aeronautical variables evaluation. A second nonlinear model, shown to be equivalent to the previous one, is derived. This model complies with the typical state space structure used for most nonlinear control design methods. Therefore, by using this model it is possible to simplify the controller design task. A disadvantage is that both models are represented by a set of highly nonlinear differential equations and may complicate the design of simple control laws. Therefore, a simplified model which is almost linear is derived. This model is based on a linear approximation of the main QRV dynamics plus a simple nonlinear term arising due to the yaw motion. Through an extensive set of simulations, the operating range of the approximate model is elucidated. It is shown that this model is adequate for linear controller design for a very wide range of operation.

Individual channel analysis of the thyristor-controlled series compensator performance

The TCSC is the electronically-controlled counterpart of the conventional series bank of capacitors. A mature member of the FACTS technology, the TCSC has the ability to regulate power flows along the compensated line and to rapidly modulate its effective impedance. In this paper its performance is evaluated using Individual Channel Analysis and Design. Fundamental analysis is carried out to explain the generator dynamic behavior as affected by the TCSC. Moreover, a control system design for the system is presented, with particular emphasis in the closed-loop performance and stability and structural robustness assessment. It is formally shown that the incorporation of a TCSC operating in its capacitive range improves the dynamical performance of the synchronous machine by decreasing the electrical distance and therefore considerably reducing the awkward switchback characteristic exhibited by synchronous generators. It is also formally proven in the paper that the inductive operation should be avoided as it impairs system operation. In general, the TCSC inclusion brings on fragility into the global system, making it non-minimum phase and introducing adverse dynamics in the speed channel of the synchronous machine. Moreover, it is shown that the minimum-phase condition may also be present in cases featuring high capacitive compensation levels.