Initial Phase Angle Research Articles

Online Diagnosis and Localization of High-Resistance Connection in PMSM With Improved Fault Indicator

This paper proposes a method for online diagnosis and localization of high-resistance connection (HRC) in permanent magnet synchronous machine (PMSM) with an improved fault indicator. In the proposed method, the amplitude and initial phase angle of zero-sequence voltage component are both analyzed. Based on the analysis, the fault indicator with angle difference is defined for fault diagnosis and localization. It is shown that not only the HRC can be detected, but also the fault severity can be assessed and the faulty phases can be identified in this method. The simulation and experiment are carried out to verify the theoretical analysis. Both the results show that the proposed method can be effectively applied for online detection and identification of the HRC in the PMSM.

Influence of the upstream slot geometry on the endwall cooling and phantom cooling of vane suction side surface

Modern gas turbines always operate at a high level of inlet temperature. The current inlet temperature in the aircraft and heavy duty gas turbines is higher than the melting point of the guide vane material. Consequently, advanced cooling schemes must be developed to ensure the safe operation of gas turbines. In the current study, numerical simulations were conducted to investigate the influence of the upstream slot geometry on the endwall cooling and phantom cooling of the vane suction side surface. Three-dimensional (3D) Reynolds-averaged Navier–Stokes (RANS) equations combined with the shear stress transport (SST) k-ω turbulence model were solved to conduct the simulations based on the validated turbulence model. The results indicate that the adiabatic cooling effectiveness in the upstream region of the stagnation is significantly increased by introducing the contoured upstream slot. However, the normal upstream slot obtains a relatively high adiabatic cooling effectiveness level in the downstream region of the stagnation. In the present research, the case with normalized amplitude A‾=0.75, initial phase angle φ=45° achieves the largest overall adiabatic cooling effectiveness near the vane leading edge. In contrast, the case with A‾=0.75, φ=30° attains the smallest overall adiabatic cooling effectiveness on the endwall surface. Moreover, the phantom cooling effectiveness on the vane suction side surface is relatively small relative to the adiabatic cooling effectiveness on the endwall. The case with the normal upstream slot achieves the largest phantom cooling effectiveness on the vane suction side surface compared with the contoured upstream slot. Overall, the contoured upstream slot significantly enhances the endwall cooling effectiveness by rearranging the distribution of the coolant mass flowrate at the slot outlet.

Accurate Compensation of Attitude Angle Error in a Dual-Axis Rotation Inertial Navigation System.

In the dual-axis rotation inertial navigation system (INS), besides the gyro error, accelerometer error, rolling misalignment angle error, and the gimbal angle error, the shaft swing angle and the axis non-orthogonal angle also affect the attitude accuracy. Through the analysis of the structure, we can see that the shaft swing angle and axis non-orthogonal angle will produce coning errors which cause the fluctuation of the attitude. According to the analysis of the rotation vector, it can be seen that the coning error will generate additional drift velocity along the rotating shaft, which can reduce the navigation precision of the system. In this paper, based on the establishment of the modulation average frame, the vector projection is carried out, and then the attitude conversion matrix and the attitude error matrix mainly including the shaft swing angle and axis non-orthogonal are obtained. Because the attitude angles are given under the static condition, the shaft swing angle and the axis non-orthogonal angle are estimated by the static Kalman filter (KF). This kind of KF method has been widely recognized as the standard optimal estimation tool for estimating the parameters such as coning angles (α1 , α2), initial phase angles (ϕ1,ϕ2), and the non-perpendicular angle (η). In order to carry out the system level verification, a dual axis rotation INS is designed. Through simulation and experiments, the results show that the amplitudes of the attitude angles’ variation are reduced by about 20%–30% when the shaft rotates. The attitude error equation is reasonably simplified and the calibration method is accurate enough. The attitude accuracy is further improved.

Class DE Voltage Driven Low $dv/dt$ Rectifier

In this paper, a Class DE voltage driven low $dv/dt$ rectifier is proposed and analyzed for the diode-on duty-cycle. The proposed Class DE voltage driven low $dv/dt$ rectifier has the advantage of low diode-voltage stress and diodes that can satisfy soft switching. Consequently, the switching loss can be reduced considerably. Equations of diodes and capacitor waveforms are obtained at the diode-on duty cycle. Moreover, the following performance parameters are obtained and clarified as functions for the diode-on duty cycle and for ${\omega }CR$ : the initial phase angle of the input voltage, the voltage and current transfer functions, the normalized input resistance and capacitance, the normalized diode current stress, and the power-output capability. In addition, the circuit design is provided and a method for calculating the power-conversion efficiency is described. With a simulation and an experiment, we derived the output voltage and the power-conversion efficiency as a function of the amplitude of the input voltage, the load resistance, and the operation frequency. The experimental results accorded with the theoretical calculations and the simulation results.

Optimized mixed-domain signal synthesis for broadband impedance spectroscopy measurements on lithium ion cells for automotive applications

Abstract. A new impedance spectroscopy measurement procedure for automotive battery cells is presented, which is based on waveform shaping. The method is optimized towards a short measurement duration, high excitation power and increased frequency resolution and overcomes limitations of established methods. For a given spectral magnitude profile, a corresponding time domain waveform is derived from the inverse discrete Fourier transform. Applying an identical initial phase angle for each frequency component, the resulting signal exhibits a high peak-to-peak amplitude at relatively low total excitation power. This limits the maximum allowed power for quasi-linear excitation. Altering the phase angles randomly spreads the excitation power across the complete measurement duration. Thereby, linearity is preserved at higher excitation power. A large set of phase patterns is evaluated statistically in order to obtain a phase pattern with a significant peak-to-peak amplitude decrease. By means of numerical optimization, even further peak-to-peak amplitude reduction is achieved. Including window functions in the synthesis concept minimizes spectral leakage without compromising the spectral signal magnitude in the frequency range of interest. A time domain waveform optimized for impedance spectroscopy on lithium ion cells is synthesized based on the proposed approach and evaluated on real automotive cells. The resulting impedance data show good concordance with established standard measurement procedures at significantly reduced measurement duration and charge throughput. Additionally, increased frequency resolution is achieved, enhancing the level of detail of the obtained impedance data. The method is used for improved localization of aging effects in the cells, without further stress of the cells by the measurement procedure.

Research on Plane Grinding under Combined Movement of X-Y Axis

There are many parameters which can influence plane grinding. It is a situation in high workload and poor realizability to find the optimization parameters of the grinding by using experimental method. Taking x-y linkage plane grinding as the platform, research on different influence of grinding quality with 4 factors including initial diameter of the abrasive, initial phase angle, lapping plate & workpiece speed ratio and x-y linkage workbench though simulation. The results show that initial radius vector of the abrasive basically has no effect on grinding trace. When speed ratio between lapping plate with workpiece is decimal the grinding trace seems much better. The significant influence of grinding quality can made by straight and helical x-y linkage motion on workbench.

Simple Zero-Sequence-Voltage-Based Cluster Voltage Balancing Control and the Negative Sequence Current Compensation Regulation Identification for Star-Connected Cascaded H-Bridge STATCOM

In some application circumstances, both positive and negative sequence reactive power compensations are desired from the star-connected cascaded H-bridge static synchronous compensator (CHB STATCOM). However, the imbalanced phase currents/voltages will cause uneven active power flow among three clusters, which makes the cluster voltage balance more challenging. In this scenario, only zero sequence voltage is available to balance the cluster voltages. Although the zero sequence voltage can be calculated in all operating conditions based on the equilibrium of the active power for each phase cluster, the calculation is definitely complicated due to the zero sequence voltage expressed in the form of trigonometric function in the abc or dq 0 frame. In this paper, the zero sequence voltage is represented in a dc form in the dq frame through introducing a virtually orthogonal zero sequence voltage. As a result, a linear relationship between the active powers and the zero sequence voltage is established, based on which, a simple zero sequence voltage calculation method is proposed with a small calculation burden. Furthermore, the accurate compensation region for the negative sequence current injection is identified by establishing the relationship between the maximum converter voltage and the negative sequence currents taking into consideration the initial phase angle of the negative sequence currents, while still keeping the cluster voltage balanced by using the zero sequence voltage control. The effectiveness of the proposed control and the compensation region are verified by the simulation and experimental results on a 400 V/±7.5 kVAr star-connected CHB STATCOM.

Study on Carbon Nanotube Dispersion Behavior in Epoxy Resin under Synergistic Effect of Continuous Stretching Flow and Ultrasound Oscillation

In this paper, carbon nanotubes (CNTs) dispersion behavior in epoxy resin under synergistic effect of continuous stretching flow and ultrasound oscillation was studied. A small continuous stretching machine which could provide continuous stretching flow for polymer was designed and manufactured for studying the synergistic effect of continuous stretching flow and ultrasound oscillation on dispersive property. Firstly, the influence of different initial phase angle of dual rotor and mixing time on dispersive property were studied by preparing specimens of CNTs/epoxy resin composite under continuous stretching machine. Then, the synergistic effect of continuous stretching flow and ultrasound oscillation on dispersive property was studied with various ultrasonic power and synergistic time. In this study, the morphology of blends was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that initial phase angle of dual rotor and mixing time had great effect on the dispersion of CNTs in epoxy resin. The degree of CNTs dispersion was best when the initial phase angle of dual rotor was 0°, and increasing mixing time could improve the degree of CNTs dispersion. Increasing ultrasonic power and synergistic time were helpful to disperse CNTs in epoxy resin. It demonstrated that the synergistic effect of continuous stretching flow and ultrasound oscillation had obviously effect on the dispersion of CNTs.

Experimental analysis of assessing of the tripping effectiveness of miniature circuit breakers in an electrical installation fed from a synchronous generator set

Due to the supply reliability concerns or to supply remote loads in some distribution networks, the synchronous generators are used as auxiliary power sources. In Poland the generators are usually connected to the network of TN (earthed neutral point) structures. Both TN-C and TN-S or their mixed arrangements TN-C-S are used. Overcurrent protection in these circuits, according to Polish and international standards and the recommendation of SEP (Association of Polish Electrical Engineers), should also act as anti-shock protection. The protection is considered to be effective (for 400V electrical installations) if the overcurrent protection trip takes less than 0.4s (maximum allowable time of touching voltage occurrence). The investigation performed by authors, showed that the producers of the generators usually use B or C characteristic circuit breakers and for large generator sets (greater than 100kVA) they recommend load split to the value of one fifth of the generator maximum power. Additionally, the most frequently excitation forcing equipment is mounted to keep short circuit current three times greater than nominal current of the generator. To assess the effectiveness of the anti-shock protection measures in circuits fed from auxiliary generator and for current lower than 32A, the set up including a self-exiting 5.5kVA and 400V generator, overcurrent protection and load was built in laboratory. The set up uses miniature circuit breakers and enables short circuits in different instants, compared to the initial phase angle of the generator voltage. Resultsof the performed short circuits showed, that for the self-excited generators (majority of small generator sets with stator current lower than 32A) the overcurrent protection cannot act as anti-shock protection, when breakers allowing full utilisation of the generator power. The alternative is to limit generator load or to introduce excitation forcing increasing device price. The proposed solution for these generators given by authors is to modify anti-shock protection system in such way, that the tripping occurs always in the time below 0.4s. Modifications include not only introduction of the measurements of currents, but also the measurements of the generator voltage. The short circuit is indicated not only by current increase, but also by voltage drop during short circuit. Experimentaldevice utilizing both measurements was build and tested for different initial short-circuit instants, with respect to the synchronous generator phase voltages. In every case, the switch-off time of the short circuit was not longer than 0.4s, what means that the protection against the risk of electric shock was effective. The settings of the device are fully adjustable, what means that levels of the measured quantities indicating trip as well as the reaction time are adjustable.

Influence of Third Harmonic Back EMF on Modeling and Remediation of Winding Short Circuit in a Multiphase PM Machine With FSCWs

For multiphase open-winding permanent-magnet (PM) machines, both back electromotive force (EMF) and short-circuit current (SCC) contain third harmonic components that interact with each other and produce even-harmonic torque pulsation. This paper investigates the impact of the third harmonic component on SCC prediction, torque pulsation and postfault remediation method in case of a winding short-circuit fault. Analytical modeling of SCC is developed, which shows that the third harmonic SCC increases the maximum value of SCC. It is found that the transient SCC is heavily influenced by the initial phase angle of winding axis and exciting current when the fault is incepted. The braking torque due to the negative q -axis SCC component is investigated, which peaks at low speed as winding inductive impedance goes down. The comparison of two postfault remediation methods for single-phase short-circuit faults shows the importance of considering the third harmonics of SCC and back EMF in terms of torque performance. Finally, the theoretical results of SCC, braking torque, and remediation methods are verified and evaluated with experimental results.

Optimization of an orbital long-duration rendezvous mission

The phasing segment of the rendezvous mission between a cargo spacecraft and a space station usually lasts for several weeks, and actually presents an orbital long-duration problem. In this study, this orbital long-duration problem is formulated as a mixed integer nonlinear programming (MINLP) problem in which the maneuver revolution numbers (integers), maneuver arguments of latitude and impulse magnitude are used as design variables at the same time. A hybrid approach is then proposed to solve this MINLP problem. First, a linear dynamics model considering the J2 term of the Earth non-spherical gravity is employed to formulate an approximate phasing problem, which is optimized using a genetic algorithm. Second, a shooting iteration process considering the coupling effect between the in-plane and out-of-plane maneuvers is proposed to improve the approximate solution to satisfy the terminal conditions of the high-precision problem. The proposed approach is demonstrated for a typical two-week rendezvous phasing mission. The results show that the proposed approach can stably obtain the near optimal high-precision solution by integrating the perturbed trajectory only a few times. Furthermore, a long-duration rendezvous phasing plan is compatible with any initial phase angles that the in-plane velocity increment remains almost unchanged when the initial phase angle changes. However, under the same conditions, the out-of-plane velocity increment has considerable variations. Compared with a two-day rendezvous phasing plan, a two-week plan could have several successive coplanar launch opportunities for the chaser by aiming different terminal revolution numbers.

Precision grinding of screw rotors using CNC method

A precision grinding method for screw rotors using a computer numerical control (CNC) grinding wheel dressing is presented in this study. A mathematical model for screw rotor grinding is developed for a prototype based on the new screw rotor grinding machine SK7032. A spatial contact curve equation for screw rotor grinding is proposed, which includes three parameters: center distance, swivel angle, initial phase angle. A parameterized program was designed by the contact curve equation, and the grinding wheel axial-section profiles were calculated for different parameters. With the calculation results, the grinding wheel profile errors were analyzed, and the maximum influence of the grinding wheel profile error was swivel angle. The minimum influence was the initial phase angle, but the position of grinding wheel profiles can be changed and the interference between the screw rotor and the grinding wheel can be avoided by its changing. A segmentation dressing method for the grinding wheel was designed based on a variable center distance, and the reasonable interval value was studied. A male rotor grinding experiment was conducted on SK7032, and the rotor profile error was measured on the gear tester P65. The results reveal that the screw rotor profile errors can be controlled within ±10 μm.

Laser-assisted Stark deceleration of polar diatomic molecules in the Χ1Σ state

The traditional Stark deceleration method is difficult to apply in chemically stable polar diatomic molecules in their ground (Χ1Σ) state because the Χ1Σ state normally experiences little Stark shift and the rovibronic ground level is mostly high-field-seeking. To solve this problem, we propose a laser-assisted Stark deceleration scheme to decelerate such molecules in the present paper. Our results show that, owing to the transverse bunching effect of the applied red-detuning laser beam, the molecules of the high-field-seeking level |J = 0, M = 0〉 in the Χ1Σ state can be effectively decelerated. Furthermore, the present scheme is more effective because the interaction between the molecules and the combined fields can produce the pseudo-first-order Stark effect, and thus increase the depth of the effective potential. Compared to those molecules in the low-field-seeking state |J = 1, MΩ = −1〉 in the usual electrostatic Stark deceleration, a higher molecular density and lower velocity can be achieved under an equivalent initial phase angle.

The influence of rock anisotropy on elliptical-polarization state of inhomogenously refracted P-wave

This paper discusses the influence of the anisotropy parameters on elliptical-polarization of the inhomogenously refracted P-wave induced at VTI-media interface. For this refracted P-wave, we have derived, the equations of the elliptical-polarization trajectory. Following the elliptical-polarization trajectory, we calculated the effects of the rock anisotropic-parameters on the polarization state, with a Poincare-sphere-like representation, for several varying media parameters. It is noted that the size, shape and initial phase angle of the elliptical-polarization trajectory are all depending the anisotropy media, as well as on the incident-angle. We expect that the findings from this paper would be applied to practical applications of seismic exploration.

A Non-Stationary Analysis of Low-Frequency Electromechanical Oscillations Based on a Refined Margenau-Hill Distribution

This paper focuses on the use of quadratic time-frequency distributions (QTFDs) to characterize the temporal variation of low-frequency electromechanical oscillations (LFEOs) using ringdown data. A refined Margenau-Hill distribution (MHD) and a procedure to extract the instantaneous frequencies and damping factors as well as initial phase angles of system low-frequency modes when the analyzed signal is multi-component are proposed. The refinement process enjoys a fast-converging iterative algorithm and without loss of generality it can be applied to other QTFDs for using in other applications. A non-stationary synthetic signal as well as simulated ringdown data of a 5-area, 16-machine power system and real measured data of Western Systems Coordinating Council (WSCC) system are used to demonstrate the efficiency of the proposed method in the presence of measurement noise.

Improved CICA algorithm used for single channel compound fault diagnosis of rolling bearings

A Compound fault signal usually contains multiple characteristic signals and strong confusion noise, which makes it difficult to separate week fault signals from them through conventional ways, such as FFT-based envelope detection, wavelet transform or empirical mode decomposition individually. In order to realize single channel compound fault diagnosis of bearings and improve the diagnosis accuracy, an improved CICA algorithm named constrained independent component analysis based on the energy method (E-CICA) is proposed. With the approach, the single channel vibration signal is firstly decomposed into several wavelet coefficients by discrete wavelet transform(DWT) method for the purpose of obtaining multichannel signals. Then the envelope signals of the reconstructed wavelet coefficients are selected as the input of E-CICA algorithm, which fulfills the requirements that the number of sensors is greater than or equal to that of the source signals and makes it more suitable to be processed by CICA strategy. The frequency energy ratio(ER) of each wavelet reconstructed signal to the total energy of the given synchronous signal is calculated, and then the synchronous signal with maximum ER value is set as the reference signal accordingly. By this way, the reference signal contains a priori knowledge of fault source signal and the influence on fault signal extraction accuracy which is caused by the initial phase angle and the duty ratio of the reference signal in the traditional CICA algorithm is avoided. Experimental results show that E-CICA algorithm can effectively separate out the outer-race defect and the rollers defect from the single channel compound fault and fulfill the needs of compound fault diagnosis of rolling bearings, and the running time is 0.12% of that of the traditional CICA algorithm and the extraction accuracy is 1.4 times of that of CICA as well. The proposed research provides a new method to separate single channel compound fault signals.

Development of a New Factor for Hot Gas Ingestion Through Rim Seal

This article presents a further investigation on the mechanism of hot gas ingestion by exploring the ingress with complicated cavity generated by the rotor-mounted cylinder protrusion. During the experiment, a cavity with 32 cylinder protrusions circumferentially distributed in rotor that contained 59 blades is applied. The annulus Reynolds number and rotating Reynolds number are fixed to be 1.77 × 105 and 7.42 × 105, respectively, while the dimensionless sealing air flow rate ranges from 3047 to 8310. The measurement of CO2 concentration and pressure is conducted. Experimental results show that the sealing efficiency is improved with the introduction of the cylinder protrusions even the static pressure inside cavity is found to be reduced. The effect of the circumferentially nonuniform cavity pressure wave is considered and added into the orifice model, and the effect of some impact factors, i.e., the amplitude, initial phase angle difference, and frequency of the cavity pressure wave, on hot gas ingestion is theoretically discussed in detail. However, it is noted that the cavity pressure wave that was introduced by 32 cylinder rotor-mounted protrusions is found to have insignificant effect on improving the sealing efficiency. In the present study, a modified orifice model that takes the tangential velocity into account is proposed and a new factor H is introduced to well explain the mechanism of the ingress.

Analysis of Class DE Current Driven Low <inline-formula><tex-math>$di/dt$</tex-math></inline-formula> Rectifier

Class DE current driven low $di/dt$ rectifier satisfies Class E switching condition and low diode current stress, which is no more than the output current. Thus, the switching loss is decreased extremely. In this paper, the Class DE current driven low $di/dt$ rectifier is analyzed for any diode-on-duty-ratio. The initial phase angle of the input current, the current and voltage transfer functions, the normalized input resistance and inductance, the normalized diode voltage stress, and the power-output capability are obtained, and clarified as the functions of the diode-on-duty ratio and those of $R/wL$ . Moreover, the power conversion efficiency and the circuit design method are shown. The circuit performance has been confirmed by the simulation results and the experimental results. In the simulation and the experiment, the characteristics of the output voltage and the power conversion efficiency against the amplitude of the input current, the load resistance, and the operation frequency have been obtained. In addition, the relationship between the equations, simulation results, and experimental results have been obtained. Theoretical, simulation, and experimental results were in good agreement with each other.

A comprehensive dynamic model to investigate the stability problems of the rotor–bearing system due to multiple excitations

In this paper, a comprehensive dynamic model is proposed to analyze the dynamic behaviors of the rotor–bearing system. Three types of excitation including the bearing waviness, the unbalanced force and the finite number of balls (varying compliance effect) are considered. Based on the extended Jones–Harris model with five degrees of freedom, the load distribution and then the stiffness of the angular contact ball bearing are obtained theoretically. After introducing the three types of excitation into the model, the bearing stiffness matrix becomes time-varying and many parametric frequencies are found due to the multiple excitations. Then, the stability problems of the parametrically excited rotor–bearing system are investigated utilizing the discrete state transition matrix method (DSTM). The simple instability regions arising from the translational and the angular motions are analyzed respectively. The effects of the amplitude and the initial phase angle of the bearing waviness, the rotor eccentricity, the bearing preload and the damping of the rotating system on the instability regions are discussed thoroughly. It is shown that the waviness amplitudes have significant influences on the instability regions, while the initial phase angles of the waviness almost have no effect on the instability regions. The rotor eccentricity just affects the widths of the instability regions. The increasing of the bearing preload only shifts the positions of the instability regions. Damping could reduce the instability regions but it could not diminish the regions completely.

Numerical Simulation of the Wake Structure and Thrust/Lift Generation of a Pitching Airfoil at Low Reynolds number via an Immersed Boundary Method

In this paper, an accurate computational algorithm in the context of immersed boundary methods is developed and used to analyze an incompressible flow around a pitching symmetric airfoil at Re=225. The boundary condition can be accurately implemented by an iterative procedure applied at each time step and the pressure is also updated simultaneously. Flow phenomena, observed at different oscillation frequencies and amplitudes, are numerically modeled and the physics behind the associated vortex dynamics is explained. It is shown that there are four flow regimes associated with four wake structures. These include three symmetric flow regimes, with adverse, favorable and no vortex effects, and an asymmetric flow regime. The phenomena associated with these flow regimes and the critical or transition Strouhal (St) and normalized amplitude (numbers are discussed. It is shown that at the fixed pitching amplitude, , Transition from adverse (drag generation) to favorable (thrust generation) symmetric flow regime occurs at St=0.23. Moreover, at this particular amplitude, transition from symmetric to asymmetric regime occurs at St=0.48. It is also shown that at St=0.22, the wake is always deflected and the flow is asymmetric for large-enough amplitudes (). The dipole vortices and lift generation are two characteristics of asymmetric vortex street. This numerical study also reveals that the initial phase angle has a dominant effect on the appearance of dipole vortices and vortex sheet deflection direction. Numerical results are in good agreement with the available experimental data.