Mitigation of Current Harmonics in Inverter-Fed Permanent Magnet Synchronous Machines with Nonlinear Magnetics

Inverter nonlinearities and machine spatial harmonics yield unwanted machine current harmonics, causing control loop instabilities, additional losses and torque ripples. In this paper a method is presented that allows online identification and compensation of both effects for anisotropic permanent magnet synchronous machines with nonlinear magnetics. The method requires no additional sensors and only fundamental component machine model parameters. It can be implemented easily in existing inverter systems by software updates. Test bench measurements show significant improvements in the whole operational area. Measurements at nominal operation result in a motor current total harmonic distortion of 0.28 % which is less than a seventh of the uncompensated value. The functional principle is transferable to other machine types or grid applications enabling the mitigation of current harmonics in a wide field of applications

A four-legs matrix converter ground power unit with repetitive voltage control

In this paper, a four-leg matrix converter is proposed as the power conversion core for aircraft ground power unit (GPU) applications. This structure allows easy management of unbalanced and nonlinear loads with minimal disruption of the power supply operation. A hybrid repetitive-traditional control system is proposed to regulate the output voltage of the GPU. This solution reduces the steady-state tracking error, maintaining fast dynamic characteristics, and increases the stability of the converter compared to conventional approaches. Simulations and experimental results from a 7.5-KW converter prototype are presented to verify the operation of the proposed configuration and to prove the effectiveness of the solution

Design of a cooperative voltage harmonic compensation strategy for islanded microgrids combining virtual admittance and Repetitive Controller

Non-linear loads (NLLs) in three-phase systems areknown to produce current harmonics at -5, 7, -11, 13… times thefundamental frequency; harmonics of the same frequencies areinduced in microgrid voltage, reducing therefore the powerquality. Dedicated equipment like active power filters can be usedto compensate the microgrid harmonics; alternatively, eachdistributed generation (DG) unit present in the microgrid can bepotentially used to compensate for those harmonics. The use of thevirtual admittance concept combined with a PI-RES controlstructure has been previously proposed as a harmoniccompensation sharing strategy when multiple DGs operate inparallel. The drawback of this methodology is that a large numberof RES controllers might be required to compensate for allharmonic components induced by NLLs, increasing the tuningcomplexity as well as the execution time. This paper proposes thecombined use of virtual admittance control loop and repetitivecontroller (RC) for harmonic compensation. The main advantageof the proposed method is that only one RC is required tocompensate for all the harmonic components, significantlyreducing the computational burden and the design complexity.The dynamic performance of the whole system is tested undervariable NLL

Analysis and design of robust stabilizing modified repetitive control systems

In control system practice, high precision tracking or attenuation for periodic signals is an important issue. Repetitive control is known as an e.ective approach for such control problems. The internal model principle shows that the repetitive control system which contains a periodic generator in the closed-loop can achieve zero steady-state error for reference input or completely attenuate disturbance. Due to its simple structure and high control precision, repetitive control has been widely applied in many systems. To improve existing results on repetitive control theory, this thesis presents theoretical results in analysis and design repetitive control system. The main work and innovations are listed as follows: We propose a design method of robust stabilizing modi.ed repetitive controllers for multiple-input/multiple-output plants with uncertainties. The parameterization of all robust stabilizing modi.ed repetitive controllers for multiple-input/multiple-output plant with uncertainty is obtained by employing H∞ control theory based on the Riccati equation. The robust stabilizing controller contains free parameters that are designed to achieve desirable control characteristic. In addition, the bandwidth of low-pass .lter has been analyzed. In order to simplify the design process and avoid the wrong results obtained by graphical method, the robust stability conditions are converted to LMIs-constraint conditions by employing the delay-dependent bounded real lemma. When the free parameters of the parameterization of all robust stabiliz-ing controllers is adequately chosen, then the controller works as robust stabilizing modi.ed repetitive controller. For a time-varying periodic disturbances, we give an design method of an opti-mal robust stabilizing modi.ed repetitive controller for a strictly proper plant with time-varying uncertainties. A modi.ed repetitive controller with time-varying delay structure, inserted by a low-pass .lter and an adjustable parameter, is developed for this class of system. Two linear matrix inequalities LMIs-based robust stability con-ditions of the closed-loop system with time-varying state delay are derived for .xed parameters. One is a delay-dependent robust stability condition that is derived based on the free-weight matrix. The other robust stability condition is obtained based on the H∞ control problem by introducing a linear unitary operator. To obtain the desired controller, the design problems are converted to two LMI-constrained opti-mization problems by reformulating the LMIs given in the robust stability conditions. The validity of the proposed method is verified through a numerical example.学位記番号：工博甲46

Application of repetitive control to the lateral motion in a roll-to-roll web system

In a roll-to-roll web system lateral motion of a web caused by disturbances, which are often periodic, results in poor product quality. To reduce the effect of such disturbances, two control strategies are applied. First, the internal model principle is used to reject a sinusoidal disturbance. Second, repetitive control theory is used to reject a general periodic disturbance. We provide the synthesis procedure for both strategies, and demonstrate its use in several simulation studies on a five-roller web system. The simulation results show that the effect of disturbances, either sinusoidal or triangular, on lateral motion are significantly reduced with the internal model controller or the modified repetitive controller

Controller design for periodic disturbance rejection

Master'sMASTER OF ENGINEERIN

Control of single- and dual-probe atomic force microscopy

“Atomic force microscope (AFM) is one of the important and versatile tools available in the field of nanotechnology. It is a type of probe-based microscopy wherein an atomically sharp tip, mounted on the free end of a microcantilever, probes the surface of interest to generate 3D topographical images with nanoscale resolution. An integral part of the AFM is the feedback controller that regulates the probe deflection in the presence of surface height changes, enabling the control action to be used for generating topographical image of the sample. Besides sensing, the probe can also be used as a mechanical actuator to manipulate nanoparticles and fabricate nanoscale structures. Despite its capabilities, AFM is not considered user-friendly because imaging is slow, and fabrication operations are laborious and often performed in open-loop, i.e. without any monitoring mechanism. This dissertation is composed of two journal articles which aim to address prominent AFM challenges using feedback control strategies. First article proposes a novel control design methodology based on repetitive control technique to accurately track AFM samples. Theoretical and experimental results demonstrate that incorporating a model of the general sample topography in the control design leads to superior tracking in AFM. Second article introduces a novel dual-probe AFM (DP-AFM) design that has two independent probes. Such a setup provides an opportunity to implement process control strategies where one probe can be used to perform one of the many AFM operations while the other probe can provide feedback by imaging the process. To demonstrate this capability, an application involving real-time plowing depth control where plow depth is controlled with nanometer-level accuracy is also presented”--Abstract, page iv