Ph.D Title

Microcomputer-Based Field Orientation Control of Induction Machine Drive System Utilizing Optimal Control Technique

Ph.D Summary

In recent years the control of high-performance induction machine drives for industry applications and production automation has received wide spread research interests. Field oriented control (FOC) of induction machine drive has been developed for high-performance industrial applications, where traditionally, only dc machine drives were available. In perfect field oriented induction machine, the coupling between the d-q axes is eliminated, hence, high-performance of the drive can be obtained. However, the decoupling characteristic of field oriented induction machine drive is sensitive to the machine parameters variations. Thus without applying more sophisticated control techniques and performance specifications, optimization for parameter insensitive property still can not be achieved.

This thesis presents modeling, analysis, design, simulation and implementation of FOC for induction machine drive system to attain optimization for parameter insensitive property. The nonlinear and linear dynamic models of the induction machine in different reference frames are derived. The dynamic analysis of the induction machine in stationary and synchronous reference frames showing the Eigen values are carried out using MATLAB and MAPLEV software. Design of the proposed controllers of currents and speed is presented with the help of the d-q transfer functions of the induction machine at FOC when driven by CRPWM inverter. The proposed controllers are based on the classical and robust H∞ control techniques. The controllers are one degree-of-freedom, (PI and IP), two degree-of-freedom, (simple lag with PI, lead-lag with PI, lead-lag & lag-lead with PI) and H∞ optimal controller based on the mixed sensitivity S/KS, S/T and S/KS/T approaches. Digital simulation of the induction machine drive system is carried out using MATLAB/SIMULINK to propose the suitable controller(s) for high-performance indirect field orientation control (IFOC) induction machine drive system considering parameter variation effect. General MATLAB Toolbox for the IFOC of induction machine drive system is created. The simulation results at different operating conditions and disturbances confirm the proposed analysis and design phase.

Design and implementation of the IFOC for induction machine drive system including software and hardware are carried out as experimental prototype for validation of the digital simulation for modeling and control. The experimental prototype consists of a microcomputer and DSP-single board, intelligent power module (IPM) three-phase IGBT inverter, driving circuits, signal conditioning circuits, transducers and the machine. The software of the control system is designed and implemented using SIMULINK for MATLAB with DS1102 DSP board in real time so that speed, IFOC, current control algorithms with different controllers, voltage command estimation algorithms and PWM control signals are all executed by microcomputer and DSP. The aim is to use the optimal-performance microcomputer and DSP-based to realize and to experimentally verify the proposed control system design methodology for IFOC induction machine drives.

The experimental results are given and recorded at different operating conditions to examine the validity of the induction machine drive system and to show agreement with the simulation results.

Scope of the Work

This thesis presents the modeling, dynamic analysis, steady state analysis, control system design, simulation and implementation of a field orientation control for induction machine drive system.

The thesis consists of eight chapters. Chapter (1) introduces an introduction to the high performance induction machine drive system requirements. The classification of the main controllers and their utilization in high performance application are given. The field orientation control principles for induction machine are also presented. The phases of control design for the induction machine drive system and the techniques for controller design are provided.

The mathematical formulation of d-q models of the induction machine in different reference frames are carried out and presented in Chapter (2). The equations of each model are derived. The state equations of the induction machine in arbitrary, stationary and synchronously rotating reference frames are developed. The signal flow diagrams of the induction machine in d-q stationary and synchronous reference frames are also provided. These diagrams show the input variables, output variables and manipulated variables and also the block diagrams of the induction machine. The dynamic analysis of the induction machine in stationary and synchronous reference frames showing the eigen values are carried out using MATLAB and MAPLEV softwares.

In Chapter (3), field orientation control dynamics of induction machine are explained. The classification of field orientation control schemes according to their types is introduced. Each type of field orientation control is discussed with the help of the block diagrams. The three orientation schemes for flux models are developed. The common types of current controllers for field orientation control are discussed with their advantages and disadvantages. The d-q transfer functions of the induction machine at field orientation in synchronous reference frame are derived in order to design the different controllers of currents, fluxes and speed.

Analysis and design of the IFOC induction machine drive system is introduced in Chapter (4). This chapter introduces the design of currents and speed controllers based on different classical control techniques using the transfer functions that are derived in Chapter (3). Different controllers have been proposed and designed based on the classical control techniques. The controllers are one degree-of-freedom , 1DOF, (PI and IP), two degree-of-freedom, 2DOF, (simple lag with PI, lead-lag with PI, lead-lag & lag-lead with PI). Chapter (5) includes the design of optimal controllers for currents and speed based on H∞ mixed sensitivity optimization control technique.

Chapter (6) introduces the simulation of all components in the IFOC induction machine drive system. The simulation is carried out using MATLAB software. The drive system components constitute a MATLAB Toolbox for the IFOC of induction machine drive system in general form. This Toolbox can be used for any induction machine with any parameters. The simulation results of the IFOC induction machine drive system are also presented in this Chapter using the different controllers for speed and currents. The study of different operating conditions and disturbances are also introduced.

The implementation phase of the indirect field orientation control (IFOC) of induction machine drive system including software and hardware is presented in Chapter (7). The hardware of the drive system components are three-phase bridge rectifier, power L-C filter to obtain pure DC source which is the input to the inverter, intelligent power module (IPM) three-phase IGBT inverter, signal conditioning circuits, isolation circuits, driving circuits, protection circuits, DSP board (dSPACE DS1102), power supply unit for the whole drive system and 1.5 kW induction machine. The software of the control system is designed using SIMULINK for MATLAB and implemented with DSP board. The program is designed to input the measuring feedback signals, the field orientation controller, current controllers, and speed controller with different techniques. Also, this Chapter deals with the experimental results of the dynamic response of the indirect field orientation control of induction machine drive system. The response of each stage in the implemented control system are presented as waveforms. Comparison between the simulation and practical results are also presented. The results confirm the proposed design procedures

The thesis covers the following novel articles:

1-The transfer function of the current loops in d-q axis and speed loop for induction machine.

2-Detailed analysis and design for the PI, IP and 2DOF controllers of current and speed using different techniques.

3-Detailed analysis and design for the Hcontrollers for current and speed.

4-Generalized IFOCIMDS Toolbox using SIMULINK for MATLAB.

5-The design and implementation of the hardware and software control program for the IFOC of induction machine drive system using DS1102 DSP board with RTI and RTW of MATLAB/SIMULINK.

Master of Science (M.Sc.)

Thesis Title:

Control of Induction Machine Using Field Orientation Technique

M.Sc. Summary

Induction machines are frequently used in variable speed drives in many applications. Field oriented control means, in general, decoupled flux linkage and torque control yielding fast torque response of ac machine to immulate dc machine. Thus induction machine can replace dc machine in various applications to get use of the numerous advantages of induction machine drive systems.

In this research vectorial models for induction machine are developed in different reference frames. The rotor flux orientation model provides purely decoupling between the flux and torque and adequate for digital implementation in field oriented control system.

The treatment of field oriented control of induction machine drives using the concepts of general flux orientation is presented for indirect (feed forward) and direct (feedback) current field orientation control. Indirect field orientation current control is thoroughly investigated for application in current regulated pulse width modulation inverter. The commonly used types of current controllers for field orientation control are the hysteresis and the ramp comparison controllers. The ramp comparison controller is preferred in this work because of the accompanied advantages.

The constant stator flux , air gap flux and rotor flux steady state operation of the induction machines treated in details with corresponding torque speed and torque slip frequency characteristics. A comparison between the three flux orientation choices is discussed in terms of torque capability and easy for implementation. Only for a constant rotor flux orientation, the mechanical characteristic is linear which makes it ideal for control applications. Parameter detuning affects the torque capability and the flux in field oriented induction machine. These effects of detuning are investigated.

The rotor flux orientation controller (the inverse of rotor flux orientation model) is more adequate to be implemented in software. Digital software and hardware required for the field orientation control are developed using 80286 microcomputer. Also, the work includes the design and implementation of the 3-phase PWM MOSFET inverter. Test results on the field orientation control and inverter when applied to a 1.5 KW induction machine are presented. The results show that the drive system has good steady state performance and capable to fulfil various application requirements.

Scope of the Work

This thesis presents the design, modelling, steady state analysis and implementation of a field orientation control for a drive system employing an induction machine.

The thesis consists of eight chapters. The vectorial and d-q models of the induction machine in different reference frames are presented in Chapter (2). The equations of each model are derived. The three orientation modes for flux models are developed.

In Chapter (3), the first basic idea of field orientation control is explained. The classification of field orientation control according to its types is presented. Each type of field orientation control is discussed with the help of the block diagrams. The common types of current controllers for field orientation control are discussed with the advantages and disadvantages of each.

Torque capabilities of field oriented induction machine are presented in Chapter (4) when using rotor flux control. These capabilities of field orientation torque are studied and investigated as function of the torque command ratio. The flux selection in field oriented induction machine is investigated in relation to the maximum torque requirements and inverter current. Normalization of flux and torque in field orientation control of induction machine is explained. The normalized equations are derived to discuss the effect of detuning.

The design and implementation of indirect field orientation controller including software and hardware is presented in Chapter (5). The coordinate transformations for field orientation controller including current controllers are developed by assembly language. Digital interfacing board and signal conditioning circuits are also presented in Chapter 5. Chapter 6 introduces the design and implementation of the 3-phase MOSFET inverter. The proposed simple driving circuitry for the inverter is presented.

Chapter (7) deals with the experimental results of the field orientation control system. The results of each stage in the implemented control system are presented as waveforms. The machine voltages and currents and the corresponding harmonic spectrum are presented also.