FLC based adjustable speed drives for power quality enhancement

This study describes a new approach based on fuzzy algorithm to suppress the current harmonic contents in the output of an inverter. Inverter system using fuzzy controllers provide ride-through capability during voltage sags, reduces harmonics, improves power factor and high reliability, less electromagnetic interference noise, low common mode noise and extends output voltage range. A feasible test is implemented by building a model of three-phase impedance source inverter, which is designed and controlled on the basis of proposed considerations. It is verified from the practical point of view that these new approaches are more effective and acceptable to minimize the harmonic distortion and improves the quality of power. Due to the complex algorithm, their realization often calls for a compromise between cost and performance. The proposed optimizing strategies may be applied in variable-frequency dc-ac inverters, UPSs, and ac drives

Power Converter of Electric Machines, Renewable Energy Systems, and Transportation

Power converters and electric machines represent essential components in all fields of electrical engineering. In fact, we are heading towards a future where energy will be more and more electrical: electrical vehicles, electrical motors, renewables, storage systems are now widespread. The ongoing energy transition poses new challenges for interfacing and integrating different power systems. The constraints of space, weight, reliability, performance, and autonomy for the electric system have increased the attention of scientific research in order to find more and more appropriate technological solutions. In this context, power converters and electric machines assume a key role in enabling higher performance of electrical power conversion. Consequently, the design and control of power converters and electric machines shall be developed accordingly to the requirements of the specific application, thus leading to more specialized solutions, with the aim of enhancing the reliability, fault tolerance, and flexibility of the next generation power systems

Cost-Effective Model Predictive Control Techniques for Modular Multilevel Converters

In this thesis, model predictive control (MPC) techniques are investigated with their applications to modular multilevel converters (MMCs). Since normally a large number of submodule (SM) capacitor voltages and gate signals need to be handled in an MMC, the MPC schemes studied in this thesis are employed for determining only the voltage levels of converter arms, while gate signals are subsequently generated by the conventional sorting method. Emphasis is given to inner-loop current control in terms of phase current and circulating current, aiming at performance enhancement and computation reduction. A variable rounding level control (VRLC) approach is developed in this thesis, which is based on a modification of the conventional nearest level control (NLC) scheme: instead of the conventional nearest integer function, a proper rounding function is selected for each arm of the MMC employing the MPC method. As a result, the simplicity of the NLC is maintained while the current regulating ability is improved. The VRLC technique can also be generalized from an MPC perspective. Different current controllers can be considered to generate the arm voltage references as input of the VRLC block, thus refining the control sets of the MPC. Based on the decoupled current models, the accumulated effect of SM capacitor voltage ripples is investigated, revealing that the VRLC strategy may not achieve a proper performance if the accumulated ripple is nontrivial compared to the voltage per level. Two indexes are also proposed for quantifying the current controllability of the VRLC. Benefiting from this analysis, A SM-grouping solution is put forward to apply such MPC techniques to an MMC with a large number of SMs, leading to an equivalent operation of an MMC with much reduced number of SMs, which significantly increases the current regulating capability with reduced complexity. As an example, the SM-grouping VRLC proposal is analyzed and its system design principles are described. This thesis also develops another MPC technique which directly optimizes the cost function using quadratic programming technique. Both a rigorous and a simplified procedure are provided to solve the optimization problem. Compared with the conventional finite control set (FCS)-MPC method which evaluates all voltage level combinations, the proposed scheme presents apparent advantage in terms of calculation cost while achieving similar performance

Development of fast multi-system simulation models for permanent magnet synchronous motor and generator drive systems

This research project investigates the development and validation of alternative simulation models for voltage source inverter fed permanent magnet synchronous machine drive systems which can rapidly and accurately analyse and evaluate the performance of PM machine drives and associated control system designs. Traditionally simulations have been conducted using switching models and state space average value methods. The simulation of switching models is time consuming and that of state space averaging involves complex mathematical transformation to d-q axis, with additional circuitry and this limits their application in a time critical design process. Even if the complex calculations of state space are overcome, the proposed model can still achieve better results. This thesis presents the development of fast multi system simulation models for permanent magnet synchronous motor and generator drive systems. The fast simulation model: Average Voltage Estimation Model (AVEM) was developed for two-level, three phase VSI-fed PMSM drive systems and two-level three phase full-scale back-back VSI incorporated in a PMSG wind energy conversion system. The method uses the principle of control strategy and switching function to derive the average phase voltage in one switching period and then uses the average voltages to drive piecewise-linear voltage sources across the terminals of the permanent magnet synchronous machine and three phase system. A voltage source inverter loss model was also developed and incorporated into the AVEM to simulate the drive system power flow and its performance evaluated. The average voltage estimation model is also used to estimate and simulate the energy output of the variable speed PMSG wind energy conversion system. Practical implementation of this technique is achieved using a DSP based controller and validation made through comparison of the DSP AVEM energy estimation method with calculated energy. The study also presents the development of detailed VSI switching models for a variable speed PMSM and a PMSG wind energy conversion system which serve as benchmarks for the proposed AVEM models. A detailed description of both models will be presented. Since models require a control strategy: these control strategies were also developed using the carrier-based sinusoidal (SPWM) and implemented with PI regulators. In the permanent magnet synchronous generator wind energy conversion system application, the SPWM is applied to control the speed of the generator side converter to track maximum power as wind speed varies using the developed passive MPPT control technique and controls the AC load side converter to maintained constant DC link voltage. The sinusoidal PWM control provides a simplified control suitable for the variable speed PMSM drive system and the PMSG wind energy conversion system. Lastly, this thesis presents a detailed development of an experimental test rig. The test rig is developed to provide flexibility for the validation and comparison of the results of both simulation models against real practical implementations for PMSM drive system and PMSG wind energy conversions system. Several simulation case studies were performed using the PORTUNUS simulation package to validate and analyse the steady state accuracy of the proposed average voltage estimation model and control system against the switching model. Experiments were also carried out to validate the results of the simulation models. The simulation models results are presented and compared with experimental results. Suitable steady state performance analysis of two-level, three phase voltage source inverter fed permanent magnet synchronous motor and two-level three phase full scale back-back voltage source inverter with permanent magnet synchronous generator drive simulation and experimental performance are also carried out. The results show good agreement of the proposed average voltage estimation model with the switching model and experimental data, and where necessary the reasons for differences are discussed. The simulation of the AVEM is approximately 50 times faster than the switching model. The limitation of the proposed model is also discussed; mainly it cannot be used for the study and analysis of the internal dynamics of the voltage source inverter. The results from the proposed modelling method utilising the average voltage estimation confirm that this method can be used as an alternative to the detailed switching model for fast simulation and steady state analysis of PM machine drive systems given the advantages of speed, simplicity and ease of implementation. Note that the proposed model is only used for steady state performance analysis; however, in future its application can be extended to transient analysis. In addition, the model is not about maximium power point tracking techniques but it can accommodate maximium power point tracking techniques. It should also be highlighted that exactly the same digital control block is used in both the switching and AVEM models thus allowing a true comparison of controller behaviour. The model developed in this research project has application beyond PMSM drive system and PMSG wind energy conversion system. It can be applied to modelling, simulation and control of other electrical machine drives such as induction machines, switched reluctance machines and three-phase VSI-fed systems

Torque Control

This book is the result of inspirations and contributions from many researchers, a collection of 9 works, which are, in majority, focalised around the Direct Torque Control and may be comprised of three sections: different techniques for the control of asynchronous motors and double feed or double star induction machines, oriented approach of recent developments relating to the control of the Permanent Magnet Synchronous Motors, and special controller design and torque control of switched reluctance machine

Performance Enhancement of Shunt APFs Using Various Topologies, Control Schemes and Optimization Techniques

Following the advent of solid-state power electronics technology, extensive usage of nonlinear loads has lead to severe disturbances like harmonics, unbalanced currents, excessive neutral current and reactive power burden in three-phase power systems. Harmonics lower down the efficiency and power factor, increase losses, and result in electromagnetic interference with neighbouring communication lines and other harmful consequences. Over the years, active power filter (APF) has been proven to be a brilliant solution among researchers and application engineers dealing with power quality issues. Selection of proper reference compensation current extraction scheme plays the most crucial role in APF performance. This thesis describes three time-domain schemes viz. Instantaneous active and reactive power (p-q), modified p-q, and Instantaneous active and reactive current component (i_d-i_q) schemes. The objective is to bring down the source current THD below 5%, to satisfy the IEEE-519 Standard recommendations on harmonic limits. Comparative evaluation shows that, i_d-i_q is the best APF control scheme irrespective of supply and load conditions. Results are validated with simulations, followed by real-time analysis in RT-Lab.In view of the fact that APFs are generally comprised of voltage source inverter (VSI) based on PWM, undesirable power loss takes place inside it due to the inductors and switching devices. This is effectively minimized with inverter DC-link voltage regulation using PI controller. The controller gains are determined using optimization technique, as the conventional linearized tuning of PI controller yield inadequate results for a range of operating conditions due to the complex, nonlinear and time-varying nature of power system networks. Developed by hybridization of Particle swarm optimization (PSO) and Bacterial foraging optimization (BFO), an Enhanced BFO technique is proposed here so as to overcome the drawbacks of both PSO and BFO, and accelerate the convergence of optimization problem. Extensive simulation studies and RT-Lab real-time investigations are performed for comparative assessment of proposed implementation of PSO, BFO and Enhanced BFO on APF. This validates that, the APF employing Enhanced BFO offers superior harmonic compensation compared to other alternatives, by lowering down the source current THD to drastically small values.Another indispensable aspect of APF is its topology, which plays an essential role in meeting harmonic current requirement of nonlinear loads. APFs are generally developed with current-source or voltage-source inverters. The latter is more convenient as it is lighter, cheaper, and expandable to multilevel and multistep versions for improved performance at high power ratings with lower switching frequencies. There can be different topologies of VSI depending on the type of supply system. With each topology, constraints related to DC-link voltage regulation change. For effective compensation, irrespective of the number and rating of DC-link capacitors used in any particular topology, voltages across them must be maintained constant with optimal regulation of DC-link voltage. Various topologies for three-phase three-wire systems (conventional two-level and multilevel VSIs) and four-wire systems (split-capacitor (2C), four-leg (4L), three H-bridges (3HB) and three-level H-bridge (3L-HB) VSIs) are analyzed and compared based on component requirements, effectiveness in harmonic compensation, cost and area of application