The Research And Implementation Of Three-phase Digital Phase-locked Loop In The Distributed Power

In order to avoid causing interference, there is need to keep the phase and frequency of the power grid voltage real-time monitoring.It ensures that the output signal of the distributed power system capture the phase and frequency of grid fundamental wave quickly and achieves synchronization with grid voltage when the distributed power system connects to the power grid. The phase-locked loop is one of the main ways to realize the above functions.In view of many designs of phase-locked loop today, by theoretical analysis, this paper first presents a three-phase digital phase-locked loop design based on structure of frequency divider on the premise of a standard grid. A combination of frequency divider, ROM trigonometric function table and look-up table method replaces the function of the voltage controlled oscillator. The output frequency, which is given by frequency divider, controlles the rate of look-up table and changes the output of the ROM table. At last, the system completes phase adjustment and avoids the use of analog circuit. According to the principle of coordinate transformation, the three-phase phase discriminator is designed, which can test the three-phase electricity directly. The whole system realizes the full digital circuit design and improves the system stability.Then, in view of the unbalance grid in the three-phase voltage situation,etc., the above three phase digital phase-locked loop was improved. A kind of three-phase digital phaselocked loop based on second-order generalized integrator is designed. Because joined the second-order generalized integrator, which has the function of frequency selective, after the three-phase phase discriminator, it can filter out the interference signal of the power grid and achieve phase lock.Finally, the design schemes are simulated in Simulink environment and the hardware experiment is carried out based on CPLD EPM570T100I5 and DSP TMS320F2808.The simulation results verifies, even if the grid appeares unbalanced three-phase voltage, the phase-locked loop will still be able to accurately and quickly capture the grid phase. Phase lock precision can meet the standards of the grid.