Photovoltaic Energy Storage System Based on Bidirectional LLC Resonant Converter Control Technology

Abstract

Bidirectional DC/DC converters are widely adopted in new energy power generation systems. Because of the low conversion efficiency and non-isolation for conventional, bidirectional DC/DC converters in the photovoltaic energy storage complementary system, this paper proposes a bidirectional isolation LLC converter topology, with compensating inductance for the energy storage system; it has excellent characteristics, such as wide input voltage range and soft switching in full-load range. First, an AC equivalent model based on the fundamental wave equivalent method is established to derive the voltage gain. Meanwhile, a small signal model is also built to design a reasonably closed-looped controller. Finally, the improved bidirectional LLC resonant converter is applied to the photovoltaic energy storage complementary system. The correctness and feasibility for the bidirectional LLC converter topology under the proposed charging and discharging control strategy of the DC bus are verified by simulation and experimental results.

Review of development and application of bidirectional LLC converter

“…Compared with the traditional PMW converter. It has the advantages of small switching loss, high efficiency, low heat loss, high economy and environmental protection, which shows great application potential in photovoltaic energy storage, new energy vehicles, aerospace and other fields [1][2].…”

A Control Design Technology of Isolated Bidirectional LLC Resonant Converter for Energy Storage System in DC Microgrid Applications

“…However, since the optimal operation point is at the resonance point, deviation from the resonance point would result in circulating losses and reduced voltage gain. Several studies [24][25][26][27][28][29] proposed an L-LLC resonant structure by adding an auxiliary inductor to the conventional LLC topology so that the resonance characteristics of each resonant mode could be LLC in both directions of operation. The power loss increased by adding an auxiliary inductor across the high voltage on the secondary side.…”

“…The CLLC [17] is similar to DAB [20], which has a higher number of switches and increased complexity of control in order to expand the output range and change from full-bridge to half-bridge and vice versa. The L-LLC [25] adds an auxiliary inductor across the high-voltage terminal on the secondary side to increase the power loss. It cannot achieve a wide voltage range because of its use of PFM control.…”

“…In addition, the asymmetric characteristics of the LLC resonant converter in the forward and backward modes are studied, and the effect of asymmetry on the resonant converter is investigated. In addition, a design method for a bidirectional LLC resonant converter is presented to reduce the need for an auxiliary inductor in the design of the backward resonant circuit shown in [24][25][26][27][28][29]. Specifically, a forward buck power flow adopts a conventional LLC resonant structure by relocating the LLC resonant tank, and a backward boost power flow employs a push-pull structure with an inductor and a capacitor in the secondary-side rectifier converter (LC-SRC) resonance by relocating the LC resonant tank.…”

Adaptive Sensorless PI+Passivity-Based Control of a Boost Converter Supplying an Unknown CPL

“…In the case of solar and wind sources, the converter is unidirectional, and it may be a buck or boost converter [5]. Battery energy storage systems must be bidirectional in nature, as the battery behaves as a load in some periods and as a power supply in others [6]. For this reason, bidirectional boost converters constitute an alternative to manage energy behavior in batteries.…”