Electric power systems are undergoing significant changes with the deployment of large-scale wind and solar plants connected to the transmission system and small-scale Distributed Energy Resources (DERs) and microgrids connected to the distribution system, making the latter an active system. A microgrid is a small-scale power system that interconnects renewable and non-renewable generating units such as solar photo-voltaic panels and micro-turbines, storage devices such as batteries and fly wheels, and loads. Typically, it is connected to the distribution feeders via power electronic converters with fast control responses within the micro-seconds. These new developments have prompted growing research activities in stability analysis and control of the transmission and the distribution systems. Unfortunately, these systems are treated as separated entities, limiting the scope of the applicability of the proposed methods to real systems. It is worth stressing that the transmission and distribution systems are interconnected via HV/MV transformers and therefore, are interacting dynamically in a complex way. In this research work, we overcome this problem by investigating the dynamics of the transmission and distribution systems with parallel microgrids as an integrated system . Specifically, we develop a generic model of a microgrid that consists of a DC voltage source connected to an inverter with real and reactive power control and voltage control. We analyze the small-signal stability of the two-area four-machine system with four parallel microgrids connected to the distribution feeders though different impedances. We show that the conventional PQ control of the inverters is insufficient to stabilize the voltage at the point-of-common coupling when the feeder impedances have highly unequal values. To ensure the existence of a stable equilibrium point associated with a sufficient stability margin of the system, we propose a new voltage control implemented as an additional feedback control loop of the conventional inner and outer current control schemes of the inverter. Furthermore, we carry out a modal analysis of the four-machine system with microgrids using Koopman mode analysis. We reveal the existence of local modes of oscillation of a microgrid against the rest of the system and between parallel microgrids at frequencies that range between 0.1 and 3 Hz. When the control of the microgrid becomes unstable, the frequencies of the oscillation are about 20 Hz. Recall that the Koopman mode analysis is a new technique developed in fluid dynamics and recently introduced in power systems by Suzuki and Mezic. It allows us to carry out small signal and transient stability analysis by processing only measurements, without resorting to any model and without assuming any linearization. / Ph. D. / Electric power systems are undergoing significant changes with the deployment of large-scale wind and solar plants connected to the transmission system and small-scale Distributed Energy Resources (DERs) and microgrids connected to the distribution system, making the latter an active system. A microgrid is a small-scale power system that interconnects renewable and non-renewable generating units such as solar photo-voltaic panels and micro-turbines, storage devices such as batteries and fly wheels, and loads. Typically, it is connected to the distribution feeders via power electronic converters with fast control responses within the micro-seconds. These new developments have prompted growing research activities in stability analysis and control of the transmission and the distribution systems. Unfortunately, these systems are treated as separated entities, limiting the scope of the applicability of the proposed methods to real systems. It is worth stressing that the transmission and distribution systems are interconnected via HV/MV transformers and therefore, are interacting dynamically in a complex way. In this research work, we overcome this problem by investigating the dynamics of the transmission and distribution systems with parallel microgrids as an integrated system . Specifically, we develop a generic model of a microgrid that consists of a DC voltage source connected to an inverter with real and reactive power control and voltage control. We show that the conventional PQ control of the inverters is insufficient to stabilize the voltage at the point-of-common coupling when the feeder impedances have highly unequal values. Furthermore, we carry out a modal analysis of the four-machine system with microgrids using Koopman mode analysis. Koopman mode analysis is a new technique developed in fluid dynamics and recently introduced in power systems by Suzuki and Mezic. It allows us to carry out small signal and transient stability analysis by processing only measurements, without resorting to any model and without assuming any linearization.

This paper will discuss the use of force apportionment to isolate modes being excited by the sine-dwell technique. The effectiveness of the apportionment technique can be determined by examining the structural response as measured by laser vibrometry. First, the structure is investigated using impact-test-based modal extraction methods. Approximate mode shapes are determined by examining the phase resonance indicator function for the resonance responses at a number of reference points. By comparing condition numbers of submatrices of the approximate modal matrix, one can select the best positions for force application. The apportioned forces for a given mode are arrived at by requiring that the input energy excite only the mode of interest while the net amount of work on adjacent modes is zero. This method is illustrated on a 24 in. x 1.5 in. x 0.375 in. steel beam. The fourth bending mode is to be separated from the first torsional mode which is 26 Hz below the bending mode. The apportioned forces are applied and laser scans are acquired of the "modal" response. The laser allows detailed investigation of the deviations of the response from the theoretical fourth mode response. The scans reveal that the force apportionment technique used in this test case fails to reliably extract the theoretical modal response of a beam. A finite element model of the beam is created to verify that the apportionment technique works. Applying an apportioned force vector to the model shows that the method is capable of isolating the mode of interest. The interaction of the electrodynamic shaker, stinger, and force transducer with the structure is investigated as a possible explanation for the failure of the technique in experimentation. It is found that there exists axial and rotatory coupling which can influence the structural response of the test specimen and decrease the reliability of the apportionment technique. / Master of Science

Presently, auto manufacturers do not have do not have efficient or accurate methods to determine the amount of refrigerant (R-134a) in an air conditioning system of an automobile. In the research presented, vibration analysis is examined as a possible method to determine this R-134a amount. Initial laboratory tests were completed and experimental modal analysis methods were investigated. This approach is based on the hypothesis that the natural frequency of the accumulator bottle is a function of the mass of refrigerant in the system. Applying this theory to a working automotive air conditioning bench test rig involved using the roving hammer method—forcing the structure with an impact hammer at many different points and measuring the resulting acceleration at one point on the structure. The measurements focused on finding the natural frequency at the accumulator bottle of the air condition system with running and non-running compressor scenarios. The experimental frequency response function (FRF) results indicate distinct trends in the change of measured cylindrical natural frequencies as a function of refrigerant level. Using the proposed modal analysis method, the R-134a measurement accuracy is estimated at ±3 oz of refrigerant in the running laboratory system and an accuracy of ±1 oz in the non-running laboratory system. / Master of Science

A new technique that couples modal analysis and wavelet transforms for detection of multiple damage in structures is introduced. Structural damage may cause local changes in one or more of the following parameters; stiffness, mass and damping that affect the dynamic behavior of the structure. For example, a crack reduces the stiffness of the structure in a localized sense, and thus reducing its natural frequency, and causes changes in both modal damping and mode shapes. In this research, two different structures have been analyzed: beams and plates. First, uniform beams with a single damage (notch) of different sizes at different locations were considered. Then, a beam with multiple damages was analyzed. Secondly, a uniform plate with a single square damage was considered. For all structures considered, the responses were obtained experimentally (using experimental modal analysis) and numerically (using finite element analysis), then wavelet transform was used to detect and characterize these defects. Most vibration-based methods require knowledge of the undamaged state of the structure, which is unavailable in most cases. However, using wavelet transformation has the advantage of not requiring knowledge of the undamaged state. In addition, wavelet transform has the characteristics that make the visualization of the signal discontinuities clear. Here it has been found that some wavelets were able to detect the damage location for all cases. Also it was observed that the magnitude of the wavelet coefficient increased linearly with the increase in the amount of damage.

Approved for public release, distribution is unlimited / Ensign, United States Navy

Findings from a project involving rotating equipment defect detection using the Algorithm of Mode Isolation (AMI) are presented. The prototypical system evaluated is a rotating shaft, supported by hydrodynamic bearings at both ends, with one disk mounted to the shaft. Shaft cracks and bearing wear are the two equipment defects considered. An existing model of the prototypical system from the literature, termed the simplified model. is modified to simulate the presence of a transverse shaft crack at mid-span. This modified model is termed the standard model. Ritz series analysis, in conjunction with a previously published description of the compliance related to the presence of a transverse shaft crack, is used to describe the decrease in shaft stiffness associated with the crack. The directional frequency response function (dFRF) is shown in the literature to provide benefits over the standard frequency response function (FRF) in both system identification and shaft crack detection for rotating equipment. The existing version of AMI is modified to process dFRFs and termed Two-Sided AMI. The performance of Two-Sided AMI is verified through system identification work using both the simplified model and a rigid rotor model from the literature. The results confirm the benefits of using the dFRF for system identification of isotropic systems. AMI and Two-Sided AMI are experimental modal analysis (EMA) routines, which estimate modal properties based on a frequency domain expression of system response. Eigenvalues and associated modal residues are the modal properties considered in the present work. Three defect detection studies are fully described. In the first, the simplified model is used to investigate bearing wear detection. Various damage metrics related to the eigenvalue and the residue are evaluated. The results show that residue-based metrics are sensitive to bearing wear. Next, the standard model is used in an in-depth investigation of shaft crack detection. When a shaft crack is present, the standard model is time-varying in both the fixed and moving coordinate systems. Therefore, this analysis is also used to evaluate performing EMA on non-modal data. In addition to continuing the evaluation of various xiv damage metrics, the shaft crack study also investigates the effects of noise and coordinate system choice (fixed or moving) on shaft crack detection. Crack detection through EMA processing of noisy, non-modal data is found to be feasible. The eigenvalue-based damage metrics show promise. Finally, the standard model is used in a dual-defect study. The system is configured with both a shaft crack and a worn bearing. One defect is held constant while the magnitude of the other is increased. The results suggest that AMI is usable for defect detection of rotating machinery in the presence of multiple system defects, even though the response data is not that of a time-invariant system. The relative merits of both input data types, the FRF and the dFRF, are evaluated in each study.

Modal parameter identification of a structure is done through modal testing and modal analysis using various system identification methods. These methods employ linear input-output relationships to extract the modes of a structure. There are cases where laboratory testing of a structure is not possible or information about the structure under operating conditions is seeked. A set of techniques called Operational Modal Analysis have been developed for modal parameter identification in operating conditions of a structure. These techniques use only response measurements to extract the modes. The aim of this study is to investigate the applicability and use of three selected time-domain methods adapted to operational modal analysis. The algorithms are programmed in Matlab&copy / environment, and various cases are evaluated using computer simulations for each method. Two of the selected methods are evaluated on a laboratory scale test setup.

The aim of this work is to determine the influence of noise on determination of own frequen-cies for machine tool by operational modal analysis. For the assigned machine tool operation-al analysis is performed using Data-Driven and Covariance-Driven method for multiple exci-tation variants. Based on the results are created stabilization diagrams used to determine ma-chine tool own frequencies. The results for each excitation variant are compared to each oth-er and the effect of noise influence on the results is determined.

CubeSat or Cubic Satellite is an effective method to study the space aroundthe Earth thanks to its low cost, easy maintenance and short lead time. However, a great challenge of small satellites lies in achieving technicaland scientific requirements during the design stage. In the present workprimary focus is given to dynamic characterization of the deployable tapespringboom in order to verify and study the boom deployment dynamiceffects on the satellite. The deployed boom dynamic characteristics werestudied through simulations and experimental testing. The gravity offloadingsystem was used to simulate weightlessness environment in theexperimental testing and simulations showed that the deployment of thesystem influence the results in a different way depending on the vibrationmode shape. / En CubeSat eller kubisk satellit är effektivt för att studera rymden runtjorden på grund av dess låga kostnad, enkla underhåll och korta ledtid. Enstor utmaningen i utformningen av små satelliter är att uppnå de tekniskaoch vetenskapliga kraven. Detta arbete har analyserat de dynamiska egenskapernahos en utfällbar band-fjäder bom i syfte att verifera och för attstudera bommens utfällningsdynamiska effekter på satellitens bana och attityd.Den utfällda bommens dynamiska egenskaper har studerats genomsimuleringar och experimentella tester. Ett tyngdkraftskompenserande systemhar använts för att simulera tyngdlöshet i de experimentella testernaoch simuleringar visar att utformningen av detta system påverkar resultatenolika beroende på svängingsmodens form.

The diploma thesis deals with determination of modal parameters for machine tool manage-ment. Experimental modal analysis is performed and a new method for determining the damping and stiffness of the machine tool guidance is proposed. A mathematical model for the calculation of signals using state equations was created and the damping stiffness was determined using hysteresis curves.