*2.1. General Objective*

The power flow calculation is a conventional method used in the power system analysis to confirm not only the power supply condition but also the status of each bus [16]. In general, it is based on the Newton–Raphson method of AC power system analysis without the consideration of grid scale as investigated in some literatures [17–21]. The optimal power flow based on an iterative method have been modified to consider recently composed DC components as revealed in [22]. The study in [22] considers a voltage-sourced converter (VSC) based on high voltage DC in the power flow equation to improve accuracy and stability in power system analysis. Meanwhile, the pure DC network also utilized an iterative method in a nodal analysis [23]. The methods are normally formed to find the DC voltage level at each node in state analysis. These processes are influenced by the scale of the system matrix in terms of calculation time, which is a major problem in the order managemen<sup>t</sup> plan of a real-time controller [24].

The aim of this paper is to present a feasibility study on the power flow analysis approach to improve accuracy of managing a hybrid system which consist of several DESs, incorporating the characteristics of main controller. Figure 1 illustrates the typical figure of the controller structure highlighting the target processes. A storage system is included in the structure connected to the main PCS with a boost chopper device. Together with the storage device, the PV modules are expected to connect to the main PCS as a hybrid form. Several current flows from DESs will form DC current (*idcn*) and be imposed on the main PCS and the measured signals (*in*) used in the highlighted section for voltage calculation.

**Figure 1.** Typical structure of a photovoltaic (PV)-energy storage system (ESS) power conversion system. PLL, phasor locked loop.

A typical control flow for VSC is applied. The measured DC voltage (*vdc*) is used in the PCS controller for grid-side, and the controller is independent of the real power control for connected DESs in the DC section. The determined reference for DC system operation (*vdc\_ref*) handles PCS signals based on measured values at grid side phasor locked loop (PLL). These control flows are for composing a PV generation system that could follow maximum power point tracking process. When a monitoring system receives a real power order from a TSO, a real power control for the entire DC system is operated independently. Without a signal correction scheme, the real power command for the ESS ignores a voltage variation in the DC section. However, based on a PV current flow signal, a modified value could be generated in this concept to decide the final reference signal for the power controller. The likely issues that may be encountered when the calculation process is applied to existing controls are illustrated in Figure 2. After constructing the line matrix for power flow analysis, a delay can be generated according to the size of the matrix for its complementation process. As the size of PV increases, the possibility of time delay is expected to increase since the calculation load for signal correction depends on the number of modules.

**Figure 2.** Description of added block for accuracy improvement method.
