Development of a Dynamic Volatge Restorer to Reduce Negative Impacts on Wind-Driven Induction Generators during and after Low-Volatge Ride through (Lvrt)

As the penetration of wind power in electrical power system increases, the impact of wind turbine operating strategy on power system stability has became a significant issue confronting the power industry. To reduce the parallel transient and resume active power balance immediately after fault clearing, the grid operator has already set the low-voltage ride through requirements for the behavior of wind turbines. Instead of disconnecting them from the grid, the turbines should remain connected to the grid and actively contribute to the system stability during and after grid faults. As compared to the doubly-fed induction generator (IG), the squirrel induction generator has the advantageous of simple control scheme, robust construction, and lower initial and run-time cost. However, the impact of ever-changing wind speed on power quality coupled with the need for excitation current make the voltage regulation difficult. Over current and unstable rotating speed caused by an IG losing excitation due to the voltage dip in the supply voltage would be difficult to contribute active power immediately after the grid faults. To sustain the excitation of the IG during the faults, a dynamic voltage restorer (DVR), with the flexibility of changing output voltage polarity, can stabilize the terminal voltage of an IG and would not contribute fault current as static synchronous compensator (STATCOM) do. The DVR is configured with a voltage-sourced inverter (VSI) and a DC capacitor. The ac side circuit of the DVR is inserted in the transmission line by a coupling transformer. Only a little electrical power is needed to sustain the capacitor voltage such that the inverter output voltage can be modulated to restore the terminal voltage of an IG continuously in both normal and fault conditions.

Project ID:PB10007-7106
External Project ID:NSC100-2221-E182-001