VARFLUX

Design, control and flux estimation on variable flux permanent magnet synchronous machines (VarFlux)

Funding institution: Ministerio de Ciencia, Innovación y Universiodades.

Participating institutions: University of Oviedo.

Dates: 01/06/2020 – 31/05/2023

Project leader: Juan Manuel Guerrero Muñoz, David Díaz Reigosa

Research team: Fernando Briz, Daniel Fernández, Carlos Suárez, María Martínez

INDEX

ABSTRACT

Permanent magnet synchronous machines (PMSM) have been the focus of significant research effort in recent years due to their superior performance, controllability, efficiency or power density, compared to other types of machines. The continuous demand of more efficient electric systems, safer and more reliable made PMSMs the primary option for traction and generation applications in multiple fields: household applications, electric traction and generation systems, military and aerospace applications. Nevertheless, efficiency of PMSMs is diminished in variable speed systems operating at high speeds as negative d-axis current must be applied in order to counteract permanent magnet (PM) flux linkage, matching the back electromotive force (Back-EMF) with the available voltage in the DC link. This mode of operation is known as flux-weakening and is characterized by an inherent copper and core loss increase; due to continuous application of negative d-axis current and the extra harmonics produced in the airgap field. Extra losses reduce the efficiency and increases the temperature of all machine parts (i.e. electric insulation, magnetization of PM…), accelerating its degradation.

To avoid the injection of flux weakening current and its subsequent adverse effects, variable flux permanent magnet machines (VF-PMSMS, also known as memory motors) have been proposed. These types of machines dynamically change the PM magnetization state (MS) during high speed operation, to reduce the need of flux weakening current what drastically reduce the induced losses.

Design optimization of a VF-PMSM becomes a complex task since power density, and the volume of permanent magnet used must be maintain compared to conventional PMSMs. At the same time, the machine must allow magnetization/demagnetization easiness to avoid overrated converters, and high demagnetization withstand capability to torque currents. VF-PMSM design relies also on the PM magnetics, electric and thermal stability. A precise characterization of the PMs is therefore key to achieve a precise, stable and safe control of VF-PMSM which is achieved when the magnetization state of the permanent magnets is accurately estimated. Therefore, the development of new PM magnetization state estimation state is a key factor for the controllability of VF-PMSMs.

El objetivo global del presente proyecto es el diseño, control, caracterización de los procesos de magnetización de los imanes y desarrollo de técnicas de monitorización del estado de magnetización de VF-PMSMs.

The main goal of the project proposal is the design and control of variable flux permanent magnet synchronous machines. This includes monitoring techniques to determine the machine magnetizing state. The proposed techniques will introduce advances both in the design and control of this type of machines. This objectives can be divided in four general goals:

- Development of flux estimation methods for variable flux permanent magnet synchronous machines.

- Development of control techniques for variable flux permanent magnet synchronous machines, including online magnetization and demagnetization strategies.

- Development of simulation models needed for the analysis of the control techniques.

Assessment of the effect of machine configuration (stator slots/rotor poles, winding design -distributed, concentrated-, magnet arrangement) on the developed techniques’ performance.

OBJECTIVES

The main goal of the project proposal is the design and control of variable flux permanent magnet synchronous machines. This includes monitoring techniques to determine the machine magnetization state. The proposed techniques will introduce advances both in the design and control of this type of machine. This objective can be divided into four general goals:

- Development of flux estimation methods for variable flux permanent magnet synchronous machines.

- Development of control techniques for variable flux permanent magnet synchronous machines, including online magnetization and demagnetization strategies.

- Development of simulation models needed for the analysis of the control techniques.

- Assessment of the effect of machine configuration (stator slots/rotor poles, winding design (distributed/concentrated), magnet arrangement) on the developed techniques’ performance.

The development of flux estimation methods for variable flux machines along with their integration in the control algorithm will decisively contribute to close the gap between research stages to industry application. That improvement will be refined with the development of online magnetization and demagnetization techniques. Both objectives will bring a performance and efficiency increase in the whole speed range of the machine. As it was stated in the previous section, the potential applications of this more efficient machine will boost the energy efficiency both in generation and traction applications; this efficiency improvement aligns with CHALLENGES (RETOS) 3 and 4 of the Spanish Strategy of Science, Technology and Innovation 2013-2020 published by the Ministry of Economy and Competitiveness (MINECO) and the European Union.

EQUIPMENT & RESULTS

FEM Model of a VF-PMSM (left) and detailed model of magnet arangemente per pole (right)

FEM Model and demagnetization coefficient for the designed VF-PMSM

Results of non-uniform demagnetization using FEM

Permanent magnet samples. Composition of hybrid magnets (from left to right): 33% AlNiCo - 66% NdFeB, 66% AlNiCo – 33% NdFeB, 66% SmCo – 33% NdFeB, and 30% AlNiCo – 70% NdFeB.

Power magnetizer equipment used to saturate and characterize magnet samples

Histeresisgrhaph, used to characterizer magnetic materials and comples composition of permanent magnets

Rotor and stator lamination laser-cut of the VF-PMSM according to the machine design.

Test bench design including a torque transducer to evaluate the efficiency of the VF-PMSM

Windind assembly of the VF-PMSM design

Real test bench after full assembly, equipped with a torque transducer and a VR resolver.

Three phase IGBT-based inverter designed to control the VF-PMSM machine

Induced voltage of phase at low speeds for differnt magnetization state values

Induced voltage of phase (magnitude) for different demagnetiziing peak values

REALTED PUBLICATIONS

C. González-Moral, J.M. Guerrero, D. Fernández, D. Reigosa, C. Rivas, F. Briz, “Realizable reference anti-windup implementation for parallel controller structures” IEEE Journal on Emerging and Selected Topics in Power Electronics, 9(4): 5055-5068, Aug. 2021. DOI: 10.1109/JESTPE.2020.3021035
D. Fernandez, Y.-G. Kang, D. F. Laborda, M. Martinez, D. Reigosa and F. Briz, “Permanent Magnet Synchronous Machine Torque Estimation Using Low Cost Hall-Effect Sensors” IEEE Trans. on Ind. Appl., 57(4): 3735-3743, July-Aug. 2021. DOI: 10.1109/TIA.2021.3075924.
Y.G. Kang and D. Reigosa, “Improving Harmonic Rejection Capability of OSG Based on n-th Order Bandpass Filter for Single-Phase System” IEEE Access, 9: 81728-81739, June 2021. DOI: 10.1109/ACCESS.2021.3085236.
D. Reigosa, Y. G. Kang, M. Martinez, D. Fernandez, J.M. Guerrero, and F. Briz, “Sensorless Control of Wound Rotor Synchronous Motors Based on Rotor High-Frequency Signal Injection” IEEE Trans. on Ind. Appl., 57(6): 6034-6043, Nov.-Dec. 2021. DOI: 10.1109/TIA.2021.3100315
M. Martinez, D. F. Laborda, D. Reigosa, D. Fernández, J. M. Guerrero and F. Briz, “SynRM Sensorless Torque Estimation Using High Frequency Signal Injection” IEEE Trans. on Ind. Appl., 57(6): 6083-6092, Nov.-Dec. 2021. DOI: 10.1109/TIA.2021.3111840.
Y.G. Kang, D. Reigosa, “Dq-Transformed Error and Current Sensing Error Effects on Self-Sensing Control” IEEE Journal on Emerging and Selected Topics in Power Electronics, 10(2): 1935-1945, April 2022. DOI: 10.1109/JESTPE.2021.3051942.
M. S. Rafaq, H. Lee, Y. Park, S.-B. Lee, D. Fernandez, D. Reigosa and F. Briz “A Simple Method for Identifying Mass Unbalance using Vibration Measurement in Permanent Magnet Synchronous Motors” IEEE Trans. on Ind. Electr., 69(6): 6441-6444, June 2022. DOI: 10.1109/TIE.2021.3088332
M. S. Rafaq, H.-J. Lee, Y. Park, S. B. Lee, M. Orviz Zapico, D. Fernandez, D. Reigosa, and F. Briz “Airgap Search Coil based Identification of PM Synchronous Motor Defects” IEEE Trans. on Ind. Electr., 69(7): 6551-6560 July, 2022. DOI: 10.1109/TIE.2021.3095810
Y. G. Kang, D. Fernandez, D. Reigosa, “Saliency-based Rotor Spatial Position Displacement Self-Sensing for Self-Bearing Machine” MDPI Sensors (ISSN: 1424-8220), 22 (24), 2022. https://doi.org/10.3390/s22249663.
J. Jeong, H. Lee, M. O. Zapico, S. B. Lee, D. D. Reigosa and F. B. del Blanco, "Trailing Edge PM Demagnetization in Surface PM Synchronous Motors: Analysis and Detection," IEEE Trans. on Ind. Appl., Accepted, publication pending, 2023.
M. O. Zapico, D. D. Reigosa, H. J. Lee, M. S. Rafaq, S. B. Lee and F. B. del Blanco, "Demagnetization Detection and Severity Assessment in PMSMs Using Search Coils Exploiting Machine´s Symmetry," IEEE Trans. on Ind. Appl., Accepted, publication pending, 2023, DOI: 10.1109/TIA.2023.3267772.

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