Non-characteristic harmonic load flow algorithm based on Newton-Raphson method for high voltage direct current system

In the non-characteristic harmonic load flow algorithm for high voltage direct current(HVDC) system, the nonlinear equations are charactered by the multivariable and huge dimension. Newton-Raphson iterative method is applied to improve the convergence of the non-characteristic harmonic load flow algorithm. The analytic expressions of three phases AC current, DC voltage, and circulation current at Δ side in Y, d transformer are deduced. According to the relationship between the AC-DC network and converter device, balance equations of three-phase harmonic current of AC bus and DC network harmonic current are deduced, the modified equation for whole system is hence constructed and solved iteratively by taking the unified fundamental and characteristic harmonic load flow as the initial value. The non-characteristic harmonic load flows of China Southern Power Grid Yunguang ± 800 kV UHVDC transmission system are evaluated to verify the reasonableness and effectiveness.