Performance-driven control of nano-motion systems

The performance of high-precision mechatronic systems is subject to ever increasing demands regarding speed and accuracy. To meet these demands, new actuator drivers, sensor signal processing and control algorithms have to be derived. The state-of-the-art scientific developments in these research directions can significantly improve the performance of high-precision systems. However, translation of the scientific developments to usable technology is often non-trivial. To improve the performance of high-precision systems and to bridge the gap between science and technology, a performance-driven control approach has been developed. First, the main performance limiting factor (PLF) is identified. Then, a model-based compensation method is developed for the identified PLF. Experimental validation shows the performance improvement and reveals the next PLF to which the same procedure is applied. The compensation method can relate to the actuator driver, the sensor system or the control algorithm. In this thesis, the focus is on nano-motion systems that are driven by piezo actuators and/or use encoder sensors. Nano-motion systems are defined as the class of systems that require velocities ranging from nanometers per second to millimeters per second with a (sub)nanometer resolution. The main PLFs of such systems are the actuator driver, hysteresis, stick-slip effects, repetitive disturbances, coupling between degrees-of-freedom (DOFs), geometric nonlinearities and quantization errors. The developed approach is applied to three illustrative experimental cases that exhibit the above mentioned PLFs. The cases include a nano-motion stage driven by a walking piezo actuator, a metrological AFM and an encoder system. The contributions of this thesis relate to modeling, actuation driver development, control synthesis and encoder sensor signal processing. In particular, dynamic models are derived of the bimorph piezo legs of the walking piezo actuator and of the nano-motion stage with the walking piezo actuator containing the switching actuation principle, stick-slip effects and contact dynamics. Subsequently, a model-based optimization is performed to obtain optimal drive waveforms for a constant stage velocity. Both the walking piezo actuator and the AFM case exhibit repetitive disturbances with a non-constant period-time, for which dedicated repetitive control methods are developed. Furthermore, control algorithms have been developed to cope with the present coupling between and hysteresis in the different axes of the AFM. Finally, sensor signal processing algorithms have been developed to cope with the quantization effects and encoder imperfections in optical incremental encoders. The application of the performance-driven control approach to the different cases shows that the different identified PLFs can be successfully modeled and compensated for. The experiments show that the performance-driven control approach can largely improve the performance of nano-motion systems with piezo actuators and/or encoder sensors

Analysis and solutions of power harmonics in medium voltage distribution networks

The transition toward more sustainable energy systems is driven mainly by greenhouse gas emissions reduction schemes and the growing demand for energy worldwide. Consequently, more Distributed Energy Resources (DER) based power sources and their enabling technologies such as Medium Voltage Direct Current (MVDC) systems are being integrated into the existing distribution networksto help meet such challenges. However, due to the presence of the Power Electronics (PE) based power converters interfacing these systems with the main power network, concerns related to power harmonics in today’s distribution networks must be addressed. To investigate the severity of power harmonics in the distribution networks with the presence of the MVDC converters, a detailed model of an MVDC converter including the switching behaviour of the semiconductor devices with a suitable control system and an interleaved Pulse-width Modulation (PWM) scheme was developed in this study. The key finding is that the proposed harmonic mitigation technique, the interleaved SPWM technique, has significantly reduced the Total Harmonic Distortion (THD) to 2% at the rated system capacity with no significant even-order harmonic components. The real data obtained from the power network of Albaha was also modelled and simulated in the frequency domain using the established harmonic models of the power system components to conductthe harmonic propagations study of the MVDC converter into the AC network. The MVDC converter harmonic performance in the Albaha power system revealed that the THDs at different voltage levels comply with the standard limits. Moreover, applications of Artificial Intelligence (AI), especially the optimization algorithms for power harmonic solutions have received considerable attention over recent years. Thus, in this research, the recently developed Manta Ray Foraging Optimization (MRFO) algorithm has been implemented for the optimal parameters design of a high-pass Passive Power Filter (PPF). An analytical harmonic analysis approach based on the Monte Carlo Simulation (MCS) was also proposed for PPF harmonic performance evaluation including uncertainties at the power network level. For the superiority validation of the MRFO algorithm, different optimizersthat have quite similar hunting and modelling strategies have been adopted. The MRFO algorithm has shown better solution-finding capability but relatively higher computational effort. By including uncertainties at the power network level, the harmonic performance of the optimally designed PPF proposed by the MRFO algorithm was investigated using a proposed MCS-based method, which has shown the significance of the PPF in terms of voltage distortions, system performance parameters, and the network’s hosting capacity for more renewable systems. The results imply that the optimally designed PPF can effectively attenuate the high-order harmonics and improved the system performance parameters over different operating conditions to continually comply with the standard limits. The proposed MCS method showed that the optimally designed PPF reduced the voltage and current distortions by roughly 54% and 30%, respectively, and improved the network hosting capacity by 10% for the worst-case scenario.Furthermore, DER-based power sources are predicted to cause significant harmonic distortions in today’s power networks due to the utilisation of power conversion systems, which are widely recognized as harmonic sources. Identifying the actual contribution of an offending harmonic source can be a challenging task, especially with multiple harmonic sources connected, changes in the system’s characteristic impedance, and the intermittent nature of renewable resources. Hence, a method based on an Artificial Neural Network (ANN) system including the location-specific data was proposed in this thesis to estimate the actual harmonic distortions of a harmonic source. The proposed method would help model the admittance of the harmonic source under the estimation, capture its harmonic performance over different operating conditions, and provide accurate harmonic distortions estimations. For this purpose, a simple power system was modelled and simulated, and the harmonic performance of a solar Photovoltaics (PV) system was used to train the ANN system and improve its prediction performance. Additionally, the expert ANN-based harmonic distortion estimator was validated in the IEEE 34-bus test feeder with different established harmonic sources, and it has estimated the individual harmonic components with a maximum error of less than 10% and a maximum median of 5.4

Intelligent control of induction motors

This thesis presents the development and implementation of an integral field oriented intelligent control for an induction motor (IM) drive using Fuzzy Logic Controller (FLC), and an Artificial Neural Network (ANN), employing a finite element controller and making use of a Proportional Integral (PI) adaptive controller as well. An analytical model of an induction motor drive has been developed. In order to prove the superiority of the proposed controller, the performance of this controller is compared with conventional PI-based IM drives. The performance of the proposed IM drive is investigated extensively at different operating conditions in simulation. The proposed adaptive PI-based speed controller’s performance is found to be robust and it is a potential candidate for high performance industrial drive applications. The novel work focuses on using a Finite Element Controller map (FECM) to manipulate adaptive controllers for motor control drives. A digital signal processing (DSP) board DS1104 and laboratory induction motor were used to implement the complete vector control scheme. The test results have been compared with simulated results at different dynamic operating conditions. The effectiveness of this control scheme has been evaluated, and it has been found to be more efficient than the conventional PI controller

Estratégia híbrida de controle para inversores trifásicos conectados à rede baseada em controladores deadbeat e proporcional+ressonante

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Elétrica, Florianópolis, 2014.Neste trabalho apresentam-se metodologias de projeto de controladores de corrente para inversores conectados à rede, incluindo um controlador proporcional+ressonante, um controlador preditivo do tipo deadbeat e uma estratégia híbrida utilizando ambos controladores. Os controladores são aplicados em um sistema inversor trifásico, dois níveis, conectado à rede elétrica por meio de um filtro indutivo-capacitivo-indutivo (LCL). As seguintes análises são realizadas: modelagem do sistema completo, efeitos de variações paramétricas, avaliação de problemas relacionado à perturbações e o comportamento do sistema para grandes variações da impedância presente na rede elétrica. Os controladores projetados são testados em um protótipo de $10~$kW, no qual avaliam-se seus comportamentos dinâmicos e a distorção harmônica total resultante. Além disso, verificam-se suas estabilidades quando conectados à uma rede elétrica com comportamento altamente indutivo.Abstract : This work presents design procedures for current controllers in grid-tied inverter applications including a proportional+resonant controller, a predictive deadbeat controller and a hybrid strategy using both concepts. The controllers are applied in a two-level three phase voltage source inverter system connected to the grid via an inductive-capacitive-inductive (LCL) filter. The following analyzes are performed: overall system modeling, effects of parametric variations, evaluation of disturbance related issues and the system behavior for large grid impedance variations. The design controllers are implemented in a 10 kW prototype. The dynamical responses are tested, the total harmonic distortion is evaluated and the performance with a highly inductive grid impedance is proven