A PLL Based Controller for Three Phase Grid Connected Power Converters

A PLL Based Controller for Three Phase Grid Connected Power Converters


The current control of three-phase grid-connected converters is typically carried out by using a proportional resonant controller or synchronous reference frame proportional integral regulator. The implementation of these controllers often requires knowledge of the grid voltage frequency/phase angle, which is typically provided by a synchronization unit. It implies that dynamics and possible inaccuracies of the synchronization unit have a considerable impact on the current controller performance. The aim of this letter is to design an adaptive current controller by using a conventional synchronous reference frame phase-locked loop (SRF-PLL). In this way, the current controller and synchronization part are merged into a single unit, which results in a simpler and more compact structure. The effectiveness of the proposed controller is verified using experimental results.


  1. Current control
  2. Distributed generation (DG) systems
  3. Phase-locked loop (PLL)
  4. Power converters
  5. Synchronization
  6. Three phase grid



Three-Phase Grid

Fig. 1. Power stage of a three-phase VSC with the proposed PLL-based controller and a harmonic/imbalance compensator.


PLL Based Controller

Fig. 2. Experimental results for the test 1.

Three Phase Grid

Fig. 3. Experimental results for the test 2.

Three Phase Grid

Fig. 4. Experimental results for the test 3.


In this letter, a PLL-based controller for grid-connected converters was proposed. This controller, which is realized by adding a positive feedback loop to the conventional SRFPLL, eliminates the need for a dedicated synchronization unit and, therefore, results in a more compact structure. To enhance the harmonic/imbalance rejection capability of the suggested controller, multiple complex integrators tuned at low-order disturbance frequencies is employed. To simplify the tuning procedure, a simple yet accurate linear model describing the frequency estimation dynamics of the proposed controller was was verified using some experimental results. The main contribution of this letter is not the proposed controller. It is actually demonstrating the possibility of making a frequency-adaptive controller from a standard PLL. The importance of this contribution will be more evident when we notice that there are a large number of advanced PLLs which can be explored for the controller design.


  • M. Carrasco, L. G. Franquelo, J. T. Bialasiewicz, E. Galvan, R. C. P. Guisado, M. A. M. Prats, J. I. Leon, and N. Moreno-Alfonso, “Powerelectronic systems for the grid integration of renewable energy sources: A survey,” IEEE Trans. Ind. Electron., vol. 53, no. 4, pp. 1002–1016, Jun. 2006.
  • Blaabjerg, Z. Chen, and S. B. Kjaer, “Power electronics as efficient interface in dispersed power generation systems,” IEEE Trans. Power Electron., vol. 19, no. 5, pp. 1184–1194, Sep. 2004.
  • K. Bose, “Power electronics and motor drives recent-progress and perspective,” IEEE Trans. Ind. Electron., vol. 56, no. 2, pp. 581–588, Feb. 2009.
  • Blaabjerg, R. Teodorescu, M. Liserre, and A. V. Timbus, “Overview of control and grid synchronization for distributed power generation systems,” IEEE Trans. Ind. Electron., vol. 53, no. 5, pp. 1398–1409, Oct. 2006.
  • Zeng and L. Chang, “An advanced SVPWM-based predictive current controller for three-phase inverters in distributed generation systems,” IEEE Trans. Ind. Electron., vol. 55, no. 3, pp. 1235–1246, Mar. 2008.