Control of Parallel Multiple Converters for Direct-Drive Permanent-Magnet Wind Power Generation Systems Major Electrical Projects

 

ABSTRACT:

This paper proposes control strategies for megawatt level direct-drive wind generation systems based on permanent magnet synchronous generators. In the paper, a circulating current model is derived and analyzed. The parallel-operation controllers are designed to restrain reactive power circulation and beat frequency circulation currents caused by discontinuous spacevector modulation. The control schemes do not change the configurations of the system consisting of parallel multiple converters. They are easy to implement for modular designs and large impedance required to equalize the current sharing is not needed. To increase the system reliability, a robust adaptive sliding observer is designed to sense the rotor position of the wind power generator. The experimental results proved the effectiveness of the control strategies.

 KEYWORDS:

  1. Circulation currents
  2. Parallel multiple converters
  3. Permanent magnet synchronous generators (PMSGs)
  4. Wind power

 SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

 Fig. 1. High-power direct-drive PMSG wind generator system connected to the power grid.

EXPECTED SIMULATION RESULTS:

Fig. 2. Same phase currents, circulating current, and dc-link voltage of two

grid-side branch units without circulating current control.

Fig. 3. Same phase currents and dc-link voltage of two grid-side branch units

under circulating current control at 10 kW full power.

Fig. 4. Generator-side currents and dc-link voltage of an individual converter

with circulating current control at 10 kW full power.

Fig. 5. 10 kW full power generating operation. (a) Grid and generator currents. (b) Suppressed circulating currents. (c) Carrier phase shifting by 180 phase at grid side.

Fig. 6. Generator-side currents of an individual converter when the generator operated at 1.5 MW. Overlapping of phase-a current of converter I in Ch1 (yellow) and phase-a current of converter II in Ch3 (pink). Ch2 is phase-b current of converter I.

Fig. 7. Three-phase generator currents of individual converter operated at 1.5 MW. Ch1(yellow) is phase-a current of converter I, Ch2 is phase-b current of converter I, and CH3 (pink) is phase-c current of converter I.

Fig. 8. Grid-side currents of individual converter when the generator operated at 1.5 MW. phase-a current of converter I in Ch1 (blue) overlapped with Ch3 (green) phase-a current of converter II. Ch2 is phase-b (red) current of converter I, dc-link voltage in CH4 (pink) 500 V/grid.

Fig. 9. Three-phase grid-side currents of an individual converter when the generator operated at 1.5 MW.

 CONCLUSION:

This paper has comprehensively addressed the control issues of parallel three-phase PWM converters for the permanent magnet wind power generation systems. The major accomplishments and some conclusions are summarized in the following.

1) A peak current model of zero-sequence currents has been derived and analyzed for the three-phase PWM converters in parallel connection.

2) A zero-sequence current control scheme has been adapted to reject the zero-sequence current inside an individual converter.

3) An adaptive observer has been integrated with parallel operation control experimentally. The performance of position sensorless control of the generator has been greatly enhanced and the reliability has been increased.

4) Zero-sequence currents have been successfully suppressed for the back-to-back converters with parallel connection. Large impedance needed to equalize the current sharing has been removed.

5) Experimental verification of the control of the three-phase PWM converters in parallel confirms the good performance and promising features of the proposed directly driven permanent magnet synchronous power generation system.

REFERENCES:

[1] T. Kawabata and S. Higashino, “Parallel operation of voltage source inverters,” IEEE Trans. Ind. Appl., vol. 24, no. 2, pp. 281–287, Mar./Apr. 1988.

[2] J. Holtz, W. Lotzkat, and K. H. Werner, “A high-power multi-transistorinverter uninterruptable power supply system,” IEEE Trans. Power Electron., vol. 3, no. 3, pp. 278–285, Jul. 1988.

[3] L. H.Walker, “10MWGTO converter for battery peaking service,” IEEE Trans. Ind. Appl., vol. 26, no. 1, pp. 63–72, Jan./Feb. 1990.

[4] S. Fukuda and K. Matsushita, “A control method for parallel-connected multiple inverter systems,” presented at the 7th Int. Conf. Power Electron. Variable Speed Drives, London, U.K., 1998.

[5] X. Kun, F. C. Lee, D. Boroyevich, Y. Zhihong, and S. Mazumder, “Interleaved PWM with discontinuous space-vector modulation,” IEEE Trans. Power Electron., vol. 14, no. 5, pp. 906–917, Sep. 1999.

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