High performance disturbance observer based control system design for permanent magnet synchronous AC machine applications

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonAn electrical machine is one of the main workforces in different industries and serves them in various applications. Machine drive control design involves many technical issues for efficient and robust exploitation. Over several decades, Permanent Magnet Synchronous Motor (PMSM) is getting preferred for industrial applications over its counterpart Squirrel Cage Induction Motor (SCIM) drive, because of their higher efficiency, power density, and higher torque to inertia ratio. In the prospective that PMSM drives are considered the drives of the future, there are still technical challenges and issues related to PMSM control. Many studies have been devoted to PMSM control in the past, but there are still some open research areas that bring worldwide researchers’ interests back to PMSM drive control. One of the approaches that may facilitate better performance, higher efficiency, and robust and reliable work of the control system is the disturbance observer-based control (DOBC) with linear and nonlinear output feedback control for PM synchronous machine applications. DOBC is adopted due to its ability to reject external and internal disturbances with improving tracking performance in the variable speed wind energy conversion system (WECS) to maximize power extraction. The high order disturbance observer (HODO) is utilized to estimate the aerodynamic torque-based wind speed without the use of a traditional anemometer, which reduces the overall cost and improves the reliability of the whole system. Also, this method has been designed to improve the angular shaft speed tracking of the PMSM system under load torque disturbance and speed variations. The model-based linear and nonlinear feedback control are used in the proposed control systems. The sliding mode control (SMC) with switching output feedback control law and integral SMC with linear feedback and state-dependent Riccati equation (SDRE) based approaches have been designed for the systems. The SDRE control accounts for the nonlinear multivariable structure of the WECS and is approximated with Taylor series expansion terms. The chattering inherited from SMC is eliminated by the continuous approximation technique. The sliding mode is guaranteed by eliminating the reaching mode in the proposed integral SMC. The model-free cascaded linear feedback control system based on the proportional-integral (PI) controllers use a back-calculation algorithm anti-windup scheme. The proposed speed controllers are synthesized with HODO to compensate for the external disturbance, model uncertainty, noise, and modelling errors. Moreover, servomechanism-based SDRE control, a near-optimal control system is designed to suppress the model uncertainty and noise without the use of disturbance observers. The proposed control systems for PMSM speed regulation have demonstrated a significant improvement in the angular shaft speed-tracking performance at the transients. Their performances have been tested under speed, load torque variations, and model uncertainty. For example, HODO-based SMC with switching output feedback control law (SOFCL) has demonstrated improvement by more than 78% than the PI-PI control system of the PMSM. The performance of the HODOs-based Integral SMC with SDRE nonlinear feedback is improved by 80.5% under external disturbance, model uncertainty, and noise than Integral SMC with linear feedback in the WECS. The HODO-based SDRE control with servomechanism has shown an 80.2% improvement of mean absolute percentage error under disturbances than Integral SMC with linear feedback in the WECS. The PMSM speed tracking performance of the proposed HODO-based discrete-time PI-PI control system with back-calculation algorithm anti-windup scheme is improved by 87.29% and 90.2% in the speed commands and load torque disturbance variations scenarios respectively. The simulations for testing the proposed control system of the PMSM system and WECS have been implemented in Matlab/Simulink environment. The PMSM speed control experimental results have been obtained with Lucas-Nuelle DSP-based rapid control prototyping kit.Center for International Program “Bolashak” of the Ministry of Education and Science Republic of Kazakhsta

Modelling, dynamics and control of a permanent magnet generator for wind power applications.

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN014115 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Model calibration of a vertical wind power plant using Dymola/Modelica

Wind energy has been used by mankind since ancient times and the last decades have seen large technological advancements in the field of wind turbines. One technology, although not very common, for harnessing the energy in the wind is the vertical axis wind turbine (VAWT). These types of turbines have not been as successful as the horizantal axes wind turbines (HAWTs) regarding efficiency and commercialization. There are however indications that the VAWTs are favorable for some applications. For researchers and developers, identifying and assessing losses occurring in a wind turbine or in any electricity generating device is important for finding potential improvements. The losses can be dependent on a range of parameters. A method has been developed in this project, focusing on vertical axis wind turbines, with the purpose to assess and quantify these parameters using Dymola. Models of the different components of a wind turbine have been developed to be used for calibration, that is, assessing the parameters. The calibration has been conducted by using the calibrate function in the Design Library in Dymola. Some of the models are based on previous master thesis work and these were translated from the SPOT library to the Electric Power Library. The data collected for the calibration were mainly synthetic data taken from a Dymola model of the entire wind turbine system, an approach using real measurement data from an AC/DC/AC-converter was also attempted. The synthetic data were used with and without added noise to check the sensitivity of the calibration process. The real measurement data were altered to be suitable for calibration. The methodology for calibration of the parameters is shown to be functional for the rotor and generator component. The calibration of the converter is troublesome since only one parameter is aecting the outputs. Calibration using synthetic data is performed, however no calibration using real data were analized

Permanent Magnet Vernier Machine: A Review

Permanent magnet vernier machines (PMVMs) gained a lot of interest over the past couple of decades. This is mainly due to their high torque density enabled by the magnetic gearing effect. This study will provide a thorough review of recent advances in PMVMs. This review will cover the principle of operation and nature of magnetic gearing in PMVMs, and a better understanding of novel PMVM topologies using different winding configuration as well as different modulation poles and rotor structures. Detailed discussions on the choice of gear ratio, slot-pole combinations, design optimisation and role of advanced materials in PMVMs will be presented. This will provide an update on the current state-of-the art as well as future areas of research. Furthermore, the power factor issue, fault tolerance as well as cost reduction will be discussed highlighting the gap between the current state-of-the art and what is needed in practical applications

Application of Scaling Laws for Direct Drive Permanent Magnet Generators in Wind Turbines

The object of this thesis is to investigate the use of scaling laws for Permanent Magnet Generators (PMGs). The product is a graphical tool named the Scaling Program, which is created in MATLAB GUIDE. The most applicable of the investigated scaling laws have been implemented in the program. The scaling laws for mass are based on work by Henk Polinder from TU Delft and the scaling laws for power and losses are based on general theory of losses in PMGs. The main contribution of the thesis is to make these scaling laws available to a user through the Scaling Program. The philosophy of the thesis is to make realistic predictions about a given reference machine, with input data limited to that which can be expected to be handed over by a generator supplier. The implemented scaling laws are able to predict the total mass as a function of the power of the generator, as well as the losses and efficiency as a function of the length and air gap diameter of the generator. The user can also manually compare power density and torque density with state of the art wind power generators. In addition the user can change parameters such as the specific cost of materials ratio of resistive losses to iron losses. This way, the output can be more finely tuned if more detailed information about the reference generator is available. The use of some aspects of the program is showcased in a section called Practical Examples. However, the user is encouraged to try out the program independently of the example. Two different philosophies are discussed concerning which parameters to change with the diameter of a reference machine. One is to keep the number of poles and slots constant while changing the pole and slot geometries with the diameter. The other is to keep the pole and slot geometries constant, and only increase the number of slots and poles as the circumferential length increase with the diameter. The first procedure opens a range of possibilities on how to change the geometry, which will alter the electromagnetic properties of the machine. Since the generator is thought to already be optimally designed in electromagnetic terms, the first procedure is deemed unpractical. Therefore only the last philosophy is applied in the scaling theory. MATLAB GUIDE is deemed to be a good tool for creating a "moderately complex" graphical user interface, which the Scaling Program can be defined as. Its versatile handling of graphical objects is especially useful. Regarding the scaling laws, the scaling of the output power is according to the theory. With a constant tangential stress, a larger rotor volume increases the output power. The scaling of the losses are shown to be more crude than necessary. According to the presented theory of losses in an electrical machine, the iron losses are dependant on the angular frequency, which for a PMG is assumed to be increasing with diameter. The use of the developed "ring-loss-method" neglects such a dependancy. The estimated efficiency increases with diameter as expected since the theory states that the output power increases with the second power of the diameter, while the losses increase with the first power of the diameter. The estimated efficiency is independent of independent of the active length. This is thought to be due to the inaccuracies in the loss-ring-method. The scaling of the mass results in similar characteristics as the paper, which the method is based on. This is however not considered a sufficient verification. Because mass of commercial multi megawatt PMGs are not available, it is difficult to verify the scaling of mass. It is difficult to verify a scaling law for wind power generators because the power levels of commercial generators today are not very large. One way could be to build a finite element model of the reference generator and implement the scaling laws into the model. This is work intensive and outside of the scope of this thesis. Another way could be to find two generators of similar design, one with a lower power rating than the other. Then try to scale up the smaller one to the same power rating as the larger machine, and compare the data of the two. This was attempted, but data on two such similar generators were not found for this thesis. Both verification methods are suggested as further work. Even though the scaling results are subjects to uncertainty due to its simplified approach the tool is deemed to fulfil its objective of showing the user which trends to expect if a reference machine is to be scaled up or down to a given power rating or geometry

A Review of Control Techniques for Wind Energy Conversion System

Wind energy is the most efficient and advanced form of renewable energy (RE) in recent decades, and an effective controller is required to regulate the power generated by wind energy. This study provides an overview of state-of-the-art control strategies for wind energy conversion systems (WECS). Studies on the pitch angle controller, the maximum power point tracking (MPPT) controller, the machine side controller (MSC), and the grid side controller (GSC) are reviewed and discussed. Related works are analyzed, including evolution, software used, input and output parameters, specifications, merits, and limitations of different control techniques. The analysis shows that better performance can be obtained by the adaptive and soft-computing based pitch angle controller and MPPT controller, the field-oriented control for MSC, and the voltage-oriented control for GSC. This study provides an appropriate benchmark for further wind energy research