###### Abstract
It is mainly related to the inverter between the PV power source and the utility grid for realizing the function of DC/AC conversion. When such faults as power failure or power trip happen, the utility grid will be disconnected, the inverter will switch to islanded operation, and the PV power source can still produce energy. It should be noted that the voltage and frequency of a PV power supply are different from the original, the condition that is defined as the so-called islanding effect [15; 16; 17]. This has negative effects, leading to the deterioration of the PV power source, utility grid, and the terminal equipment simultaneously. In order to overcome the influence of islanded operation, many studies focus on islanding detection techniques [18; 19; 20; 21]. In [19], the recognition of islanding and operational events in a power system with renewable energy penetration was investigated, and a detailed study concerning the islanding estimation was undertaken. At present, its idea is mainly based on passive comparison; i.e., an appropriate threshold value is selected for the comparison purpose and performs the analysis. In [21], a serial of approaches based on the signal processing algorithms were utilized for renewable energy system applications. In [22], a comparative study was presented for often-used approaches in the aspects of merits, limitations, practical applicability, cost, and accuracy. Although the islanded operation in the grid-connected PV systems is preferentially avoided in advance, it is difficult to prevent. Therefore, if it occurs in an unexpected PV access point with different penetration rates, how it affects the performances of the PV power supply, node voltage, and branch loss is an interesting issue but one seldom investigated. Based on the above analysis, this paper aims to investigate the effects of different PV integration points and PV penetration levels on the safety, steady-state performance, and system losses of grid-connected PV systems and proposes a simplified analytical method and PV configuration optimization approach suitable for practical engineering applications. The contributions of this paper can be summarized as follows:* For the typical grid-connected PV power system with three-level structure, a network topological model is established;
* The relationship of the PV, node voltage, and node voltage deviation in accordance of different access points and penetration rates of PV power supply are deduced in cases of steady working condition;
* A simplified system model is proposed to study the relationship between system losses and PV energy, including the connection location, capacity, and reactive power of PV;
* A PV segmentation strategy for the integration of large-capacity PV is proposed. This paper is organized as follows. Section 2 introduces a conventional distribution network, which will serve as the theoretical derivation proof and conclusion verification object for this article. Section 3 focuses on node voltage as an objective and presents the potential issues that distributed PV integration may introduce to the system's energy distribution, along with a preliminary verification. Section 4 introduces the conversion of the power system into a simplified equivalent circuit and derives the formula for the maximum PV power that can be provided without causing voltage rise. Section 5 provides the calculation formula for the reactive power that the system needs to absorb when it is necessary to further increase the PV power output [23; 24]. Section 6 introduces several methods for determining the size, separation, and operation of PV power sources within the distribution network using the formulas derived in Section 4.2.