Power distribution systems are experiencing a largescale integration of Converter-Interfaced Distributed Energy Resources (CIDERs). This complicates the analysis and mitigation of harmonics, whose creation and propagation are facilitated by the interactions of converters and their controllers through the grid. In this paper, a method for the calculation of the so-called Harmonic Power-Flow (HPF) in three-phase grids with CIDERs is proposed. The distinguishing feature of this HPF method is the generic and modular representation of the system components. Notably, as opposed to most of the existing approaches, the coupling between harmonics is explicitly considered. The HPF problem is formulated by combining the hybrid nodal equations of the grid with the closed-loop transfer functions of the CIDERs, and solved using the Newton-Raphson method. The grid components are characterized by compound electrical parameters, which allow to represent both transposed or non-transposed lines. The CIDERs are represented by modular linear time-periodic systems, which allows to treat both grid-forming and gridfollowing control laws. The method's accuracy and computational efficiency are confirmed via time-domain simulations of the CIGR É low-voltage benchmark microgrid. This paper is divided in two parts, which focus on the development (Part I) and the validation (Part II) of the proposed method.

No abstract

No abstract

As known, nonlinear loads in power systems originate harmonic distortion and power quality issues. Converterinterfaced loads exhibit a nonlinear behaviour as well and may largely contribute to increase the harmonic pollution. The nonlinearities introduced by the PLL-synchronization and power control originate, indeed, a coupling mechanism between fundamental and harmonic frequencies. These harmonic coupling effects are not captured by traditional Norton/Thevenin equivalent converter models, leading to inaccurate harmonic power flow analyses. This paper proposes a Linear Time Periodic model of a PLL-synchronized converter to be used in Harmonic Power Flow analyses. A realistic 18-bus distribution grid hosting substantial amount of power-electronic interfaced resources is used as a case study. It is revealed that, in high grid loadability condition and with distorted grid supply voltage, the harmonics are significantly amplified by the converters and the fundamental components of the buses voltages are reduced, representing a risk for the voltage stability. This phenomenon is also influenced by the tuning of the current control loop and the PLL. The accuracy of the presented analyses is validated by comparing the harmonic power flow results with time-domain simulations.