Janne Heikkinen

Commissioning and Control of the AMB Supported 3.5 kW Laboratory Gas Blower Prototype

This paper presents the practical results of the design analysis, commissioning, identification, sensor calibration, and tuning of an active magnetic bearing (AMB) control system for a laboratory gas blower. The presented step-by-step procedures, including modeling and disturbance analysis for different design choices, are necessary to reach the full potential of the prototype in research and industrial applications. The key results include estimation of radial and axial disturbance forces caused by the permanent magnet (PM) rotor and a discussion on differences between the unbalance forces resulting from the PM motor and the induction motor in the AMB rotor system.

Twice-Running-Speed Resonances of a Paper Machine Tube Roll Supported by Spherical Roller Bearings: Analysis and Comparison With Experiments

Imperfections in a rotor-bearing system may cause undesirable subcritical resonances occurring when the rotating speed of the rotor is a fraction of the natural frequency of the system. These resonances arise partly from rotor imperfections and partly from bearing imperfections. This study demonstrates that the subcritical twice-running-speed vibrations originating from bearing waviness may be investigated by combining a simplified rotor model with a detailed bearing model, using a finite element method. The rotor-bearing system under investigation is a roller test rig consisting of the tube roll of a paper machine supported by spherical roller bearings. The bearing waviness from the second to the fourth orders is emulated as accurately as possible in the finite element model. This is achieved by measuring the waviness of the real bearings and then incorporating the measurement results into a simulation model. The tube roll of the test rig is modeled as a symmetric tube, neglecting the effects of the uneven mass and stiffness distribution of the roll. The contact between the rotor and the bearings is described using nonlinear Hertzian contact theory. The subcritical responses of the system are studied by means of time integration, and the results are converted into the frequency domain using fast Fourier transformation. The results of the analysis are compared with the measurement results for the subcritical responses of the roll. The agreement between the simulation and experimental results of the studied system can be observed even though rotor imperfections are not considered.© 2014 ASME

Stresses of an AMB-Supported Rotor Arising From the Sudden Contact With Backup Bearings

High speed technology has a fundamental advantage when compared to conventional motors. Active magnetic bearings (AMBs) are often needed in the high speed motors, as they can provide almost frictionless support and allowing control for the dynamics of the system. AMBs require backup bearings to avoid damage resulting from a failure in the component itself, in the power system, or in the control system. During a rotor-bearing contact event, substantial impact forces may occur between the backup bearing and the rotor.In this study the rotor model is implemented using a finite element approach including backup bearings which are modelled as simplified cageless ball bearings. Based on results of this study, the increase in backup bearing misalignment can have proportional impact on the rotor bending and shear stresses in touchdown situation.Copyright

Layered Sheet-Steel Damping Estimation Using Optical Vibrometry

A non-contact modal analysis method is implemented to estimate the structural damping ratios for four stacks of sheet-steel, each bound using a different method. The setup comprised the four subject stacks and, for comparison, two single homogeneous steel plates of the same length and width with thicknesses that approximated the layered stack heights. To carry out the modal analyses, each test item was hung to simulate a free-free boundary condition. A force and frequency adjustable impact hammer imparted transient vibration to each hanging test piece after which the local relative velocity for each one of an array of discrete target points across the entire length-to-width surface was measured using an optical transducer. Damping ratios were extracted from the frequency response curves using the half power bandwidth method. Comparing the results obtained for the layered sheet-steel stacks with those from the homogeneous steel plates showed that damping ratios and loss factors can be estimated using the proposed experimental technique. The consistent impacts and the elimination of test structure mass loading improves the accuracy of damping estimates. In comparison to the solid plates, the layered sheet-steel stacks were characterized by increased damping. The effect was most significant for the stack bound together by polymer rivets.Copyright

Indirect water cooling system improvements for vehicle motor applications

This study introduces indirect water cooling systems and their improvements utilized in proto typing of vehicle machines. Due the vehicle machines require high torque at acceleration they are often equipped with indirect liquid cooling. One common method to implement liquid cooling is a water jacket inside machine frame as well as on the end plates. The flow rate of different cooling systems are studied. The cooling is improved in a radial machine by removing excessive material from rotor, adding copper heat paths in the rotor and by increasing the liquid cooling channel volume in the frame. Axial machine is utilized to study the cooling improvements with copper heat paths in stator and potting material. Measurements and results are presented for a permanent magnet 110 kW radial machine and for a permanent magnet 75 kW axial machine.

Rotordynamics of a Trans-Rotary Magnetic Gear Rotor

Trans-Rotary Magnetic Gear (TROMAG) has recently been introduced as a reliable and efficient way of converting low-speed, high-force translation into high-speed, low-torque rotation, or vice versa. The gear can be used in any high force linear motion application; specifically, it would be a strong contender for wave energy harvesting. The TROMAG consists of two main parts: a rotor and a translator, both of which are formed by furnishing tubular ferromagnetic iron cores with helically-disposed permanent magnets. In this paper, the dynamics of the rotor is studied by employing the Finite Element Method (FEM) and using a simplified model where a flexible rotor is spinning on the flexible isotropic bearings. The rotor system has non-idealities that may excite the system to vibrate. In addition, the non-idealities in geometry cause uneven magnetic pulling force that is considered as an external force. The transient response of the rotor-bearing system is studied by varying the eccentricity of the rotor with respect to the translator. The vibration characteristics of the rotor-bearing system of the TROMAG are evaluated and presented in this paper.Copyright

Subcritical Twice-Running-Speed Vibrations of a Non-Ideal Rotor-Bearing-System: Simulation and Experiments

Subcritical twice-running-speed resonances of a paper machine tube roll are studied in this paper. Resonances arise partly from the non-idealities of the rotor and partly from the non-idealities of the bearings. Resonances are affecting the quality of end product and therefore have to be studied precisely. The complex rotor-bearing system is modeled by using a flexible multibody simulation approach. Non-idealities of the rotor-bearing system are measured from the existing structure under investigation and the parameters of the real structure are emulated as accurately as possible in the simulation model. The simulation model is verified using the results from experimental modal analysis and the measurement results for the subcritical twice-running-speed response of the roll. The inertia modeling of the flexible rotor is also studied. It is found that inertia coupling between the rigid body rotation and body deformation must be included into analysis in order to achieve accurate results.Copyright

Dynamic Analysis of a Direct-Driven Permanent Magnet Generator Drive Train Including Flexible Turbine Blades

The dynamic torque of a wind turbine drive train with a direct-driven permanent magnet synchronous generator is analyzed in this paper. A simplified multi-mass model for the whole drive train — from the flexible turbine blades to the rotor of the generator — is presented. Dynamic torque is analyzed for both steady state and transient cases. In the mechanical model, torsional electromagnetic forces called “cogging torque” and “torque ripple” are used as excitation forces. The magnitude of electromagnetic excitation is highly related to the shape and placement of the magnets. Four different permanent magnet installations are analyzed. It can be noticed that during start-up only cogging torque affects the generator rotor. Allowable cogging torque in this case is 1.5–2 percent of the rated torque even when the corresponding resonance frequency does not occur in the operational speed range of the wind turbine. Furthermore, it was perceived that the resonance caused by the excitation torque should occur at the lowest possible speed to minimize dynamic torque during the start-up. Several excitations, both cogging torque and torque ripple harmonics, occur in the operational speed range. However, it was detected that the dynamic responses in the operational speed range are not critical to the operation of the wind turbine.Copyright

Vibration Effect by Unbalanced Magnetic Pull in a Centrifugal Pump with Integrated Permanent Magnet Synchronous Motor

Unbalanced magnetic pull (UMP) effect in a permanent magnet synchronous machine (PMSM) is investigated. The force model is established analytically based on previously studied model by modulating the fundamental magnetomotive force (MMF) wave by air gap permeance and the corresponding force components are evaluated via Maxwell stress tensor method. For considering real rotor dynamic condition, mixed (i.e. static and dynamic) and axial-varying eccentricity are modeled. The rotor bearing system including this UMP model is established by two methods. In the first method, UMP is included as a linear negative spring in the rotor model, while in the second method, the UMP is added as an external force. Rotor dynamics of a centrifugal pump driven by integrated PMSM is modeled using beam elements and different modeling approaches for UMP are applied. From the results, vibration effect of UMP is investigated and difference between two methods is interpreted. For verifying the analysis results, experimental work is conducted for the pump test rig, where the eccentricity condition are produced and the frequency spectra result are obtained. Through these analysis and experimental work, negative stiffness effect and additional vibration excitation by UMP are observed and interpreted.

A Case Study of the Contact Force and Stress in the Backup Bearing of a Generator: Experimental Study and Numerical Simulation of Dropdown

This paper presents both experimental and numerical study on the dropdown of a generator rotor in a two-stage radial gas turbine utilizing AMB system. The simulation unifies the FE-model of the flexible rotor and the dynamic model of backup bearings. The system under investigation includes a flexible rotor, an axial and two radial AMBs and two backup bearings, double row angular contact ball bearings. The recorded behavior of the studied rotor in the sudden failure of the electromagnetic field is demonstrated. Furthermore, the fine-tuned rotor-system model is used for studying the contact force and the contact stress in the backup bearing. The comparison between the measured results and the simulated results confirms that the used simulation tool can be applied for the design consideration of rotor-backup bearing system and enables to investigate the effect of various design parameters on the dynamic behavior of rotor in the dropdown.