An approach for handling the nonlinearities of HVDC system for stability analysis

An approach for linearizing the nonlinearities of the high voltage direct current (HVDC) system for analyzing the system stability over wide range of operation is presented. The nonlinearities can be linearized with ±5% error over a wide range of system operation. It is shown that the nonlinearities introduced by the converter, real power, and reactive power equations can be linearized over a wide range by using the integral square error (ISE) method. The results are compared with standard techniques called small signal analysis. It is shown that the stability margin of the system predicted by the new technique is relatively smaller than what is predicted by small signal analysis. The system stability boundaries are determined by the AC voltage and the reactive current control. These two control schemes may provide the same stability margin, provided appropriate controller gains are selected. The power factor control modeling is discussed