A Reliable Modular Based PV-Battery Hybrid System with Peak Shaving Capability

Abstract

The driving factors in emerging photovoltaic (PV) systems and battery-energy-storage systems (BESS) are highly scalable feature, modular and flexible structures with superior transformerless performance. The feasibility of Modular Multilevel Converter (MMC) to operate without overall DC-link allows the integration of PV generators and battery strings with its submodules (SMs), whereas each SM acts as an independent voltage source due to its ability to insert/bypass the isolated DClink capacitor. In this paper, MMC topology based-split BESS along with distributed PV generators, integrated into each SM is proposed. The presented flexible energy conversion system extracts the maximum power from all distributed PV generators under substantial partial shading and allows the peak shaving to match the intermittent PV power with the variable power demand from the smart grid. With the absence of common DC-link and presence of large arm power variations, the introduced distributed PV-battery system provides balanced three-phase sinusoidal currents to the grid. A five-level three-phase MMC with proposed distributed PV-battery hybrid topology is developed. The simulation results under fast variations in solar irradiance and power demand by the grid are included, which demonstrate its superior performance.

Power Scheduling Method for Grid Integration of a PV-BESS CHB Inverter With SOC Balancing Capability

“…The practical implementation can find a suitable solution in multilevel inverters (MLI), in which the energy storage elements can be integrated in a distributed way, with evident advantages in terms of power control and management [15], [16]. When using the MLI topology, the power fluctuation problem can be addressed in two different ways: in some solutions there is full integration of the batteries and the PV panel, i.e., one group for each submodule (i.e., inverter stage) of the MLI [17], [18], [19]; other solutions provide for partial integration, with one or more batteries connected to the dc-link instead of to the PV panel [20], [21], [22] (so-called hybrid system). However, in all cases mentioned, the integration of each battery always requires an interface dc/dc converter capable of managing the charging/discharging phases during operation.…”

“…A unidirectional dc/dc converter is used only for the connection of the photovoltaic generator (PVG) to the dc-link. The proposed circuit configuration in PV-BESS CHB inverter represents a novelty with respect to the solutions of [17], [18], [19], [20], [21], [22].…”

PV Module-Level CHB Inverter with Integrated Battery Energy Storage System

“…one central battery. This translates also into the possibility of shortening the battery strings so mitigating issues related to overcharging, overheating and reducing the risk of shutdown due to failure of a single battery cell [23,24], also accomplished with the voltage converter output, while using low voltage batteries [25]. The existence in CHB circuit topology of dedicated lower voltage dc buses facilitates the battery integration into the converter, by obtaining a distributed storage system, which can exploit the features of the multilevel configuration, such as modularity, redundancy, and flexibility.…”

“…In our case, the backup module consists of a battery and a bidirectional dc-dc converter which allows the battery charging/discharging mode in order to reduce the intermittency of PVGs [24]. In particular, a short term variability of PV generation profile has been considered, so leading to reduced size and weight of the battery which is intended to mitigate the PV power fluctuations in a timescale up to tens of minutes.…”