Linear alternators (LAs) coupled to thermoacoustic engines (TAEs) provide a viable solution to extract energy from a heat source in a variety of applications such as waste heat, energy harvesting, solar thermal and biomass power generation. For the electrical power to be maximised, the acoustic impedances of LA and TAE have to match. This requirement cannot, in general, be met by relying only on the design of the LA, but can be achieved at the control level, by using a fraction of the LA inverter current to create ‘electronic stiffness’ which contributes to the overall stiffness tuning the resonance frequency. The same concept can, in principle, be used to replace part of the mechanical spring stiffness in order to overcome the limitations in the mechanical design, at the expense of an increase in LA and inverter ratings. The impact of electronic stiffness on LA power capability and ratings is analysed here. Two meaningful scenarios are considered in the analysis: the LA derating for resonance frequency tuning and the oversizing when springs are partially replaced by electronic stiffness. The study is supplemented with experiments on a small-scale LA test rig.

References

1. 1)
  - 7. Polinder, H., Mecrow, B.C., Jack, A.J., et al: ‘Conventional and TFPM linear generators for direct-drive wave energy conversion’, IEEE Trans. Energy Convers., 2005, 20, (2), pp. 260–267.
2. 2)
  - 5. Wang, J., West, M., Howe, D., et al: ‘Design and verification of a linear permanent magnet generator for free-piston energy converter’, IEEE Trans. Energy Convers., 2007, 22, (2), pp. 299–306.
3. 3)
  - 20. Zangh, M., Iacchetti, M.F., Shuttleworth, R.: ‘Novel maximum power point tracking strategies for electronically-tuned linear alternators’. 9th IET Int. Conf. on Power Electronics, Machines and Drives, Liverpool, UK, 2018.
4. 4)
  - 19. Wang, K., Zhang, J., Zhang, N., et al: ‘Acoustic matching of a traveling-wave thermoacoustic electric generator’, Appl. Thermal Eng., 2016, 102, (5), pp. 272–282.
5. 5)
  - 15. Daboussi, Z.: ‘An inverter-based sensorless controller for free-piston stirling engines’. 35th IEEE Power Electronics Specialists Conf., Aachen, Germany, 2004, pp. 1707–1710.
6. 6)
  - 22. Chen, N., Chen, X., Wu, Y.N., et al: ‘Spiral profile design and parameter analysis of flexure spring’, Cryogenics, 2006, 46, (6), pp. 409–419.
7. 7)
  - 17. Lewis, T.M., von Jouanne, A., Brekken, T.K.A.: ‘Per-unit wave energy converter system analysis’. 2011 IEEE Energy Conversion Congress and Exposition, Phoenix, AZ, 2011, pp. 4123–4129.
8. 8)
  - 4. Zheng, P., Tong, C., Bai, J., et al: ‘Electromagnetic design and control strategy of an axially magnetized permanent-magnet linear alternator for free-piston stirling engines’, IEEE Trans. Ind. Appl., 2012, 48, (6), pp. 2230–2239.
9. 9)
  - 2. Xia, J., Li, W., Peng, R., et al: ‘Analysis on axial end flux leakage and resonance characteristic of TFPM linear generator for thermoacoustic electric generation system’, IEEE Trans. Magn., 2016, 52, (12), pp. 1–7.
10. 10)
  - 18. Lewis, T.M., von Jouanne, A., Brekken, T.K.A.: ‘Wave energy converter with wideband power absorption’. 2011 IEEE Energy Conversion Congress and Exposition, Phoenix, AZ, 2011, pp. 3844–3851.
11. 11)
  - 3. Wang, D., Shuttleworth, R.: ‘Linear alternator design for use in heat energy recovery system’. 6th IET Int. Conf. on Power Electronics, Machines and Drives, Bristol, UK, 2012.
12. 12)
  - 12. Shek, J.K.H., Macpherson, D.E., Mueller, M.A., et al: ‘Reaction force control of a linear electrical generator for direct drive wave energy conversion’, IET Renew. Power Gener., 2007, 1, (1), pp. 17–24.
13. 13)
  - 10. Nie, Z., Xiao, X., McMahon, R., et al: ‘Emulation and control methods for direct-drive wave energy converters’, IEEE Trans. Ind. Inf., 2013, 9, (2), pp. 790–798.
14. 14)
  - 8. Vermaak, R., Kamper, M.J.: ‘Experimental evaluation and predictive control of an air-cored linear generator for direct-drive wave energy converters’, IEEE Trans. Ind. Appl., 2012, 48, (6), pp. 1817–1826.
15. 15)
  - 21. Tedeschi, E., Molinas, M.: ‘Impact of control strategies on the rating of electric power take off wave energy conversion’. 2010 IEEE Int. Symp. on Industrial Electronics, Bari, 2010, pp. 2406–2411.
16. 16)
  - 11. Brooking, P.R.M., Mueller, M.A.: ‘Power conditioning of the output from a linear vernier hybrid permanent magnet generator for use in direct drive wave energy converters’, IEE Proc. Gener. Transm. Distrib., 2005, 152, (5), pp. 673–681.
17. 17)
  - 9. Yu, Z., Jaworsky, A.J., Backhaus, S.: ‘Travelling-wave thermoacoustic electricity generator using an ultra-compliant alternator for utilization of low-grade thermal energy’, Appl. Energy, 2012, 99, pp. 135–145.
18. 18)
  - 1. Swift, G.W.: ‘Thermoacoustic engines’, J. Acoust. Soc. Am., 1998, 84, (4), pp. 1145–1180.
19. 19)
  - 13. Shek, J.K.H., Macpherson, D.E., Mueller, M.A.: ‘Experimental verification of linear generator control for direct drive wave energy conversion’, IET Renew. Power. Gener., 2010, 4, (5), pp. 395–403.
20. 20)
  - 6. Sa Jalal, A., Baker, N.J., Wu, D.: ‘Design of tubular moving magnet linear alternator for use with an external combustion – free piston engine’. 8th IET Int. Conf. on Power Electronics, Machines and Drives, Glasgow, UK, 2016.
21. 21)
  - 14. Wu, F., Zhang, X.-P., Ju, P., et al: ‘Modelling and control ow AWS-based wave energy conversion system integrated into power grid’, IEEE Trans. Power Syst., 2008, 23, (3), pp. 1196–1204.
22. 22)
  - 16. Zheng, P., Yu, B., Zhu, S., et al: ‘Research on control strategy of free-piston stirling-engine linear-generator systems’. 17th Int. Conf. on Electrical Machines and Systems, Hangzhou, China, 2014, pp. 2300–2304.

Volt-ampere ratings in electronically tuned linear alternators for thermoacoustic engines

References

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