Narrow Band State of Charge (SOC) Control Strategy for Hybrid Container Cranes

Abstract

This paper evaluates possibility of using a new hybrid system based on variable speed diesel generator (VSDG), Li-ion battery bank and supercapacitor bank (SC) for a rubber tire gantry crane (RTGC) used in container terminals. Existing commercial hybrid systems face difficulties producing high efficiencies, higher life span, and lower initial investment cost due to inheriting characteristics of batteries and supercapacitors. In the proposed power system, a variable speed diesel generator act as the principal energy source, while a Li-ion battery bank and SC bank act as an energy storage system. The battery supports the diesel generator during steady demand and further, it absorbs a part of energy during regeneration. The energy management strategy, control the power flow from different sources while maintaining battery state of charge (SOC) level within a narrow band. Unlike most battery systems, this narrow band operation of battery system increases its life span while reducing capacity fade. The originality of this study can be emphasized from this narrow band SOC control technique. Simulation results for real operational load cycles are presented showing a stable system operating under defined current limits which can enhance lifetime of battery system and increase fuel saving by downsizing 400 kW constant speed diesel generator to 200 kW VSDG.

Game-Based Energy Management Method for Hybrid RTG Cranes

“…Hybrid system: DG, battery, SC 0.258 -Hybrid system: VSDG, battery, SC [6] 0.85 70.6 Hybrid system: DG, battery [8] 0.405 36.3 Conventional system: single DG [8] 0.95 72.8…”

“…The three devices of DG, lithium battery, and SC were modeled as three agents in the game, and this method could adequately reflect and meet the different preferences of the devices in energy management. The method proposed in Reference [6] also involved three types of devices. A state machine method was used in Reference [6] to control the operations of devices by performing a state transition based on the SoC and load current information.…”

“…The method proposed in Reference [6] also involved three types of devices. A state machine method was used in Reference [6] to control the operations of devices by performing a state transition based on the SoC and load current information. The conditions for determining state transitions were fixed for a determined system.…”

“…The lithium battery is a kind of energy storage device with high energy density. The SC has a low energy density but a high power density and a high dynamic response [6]. The SC can deal with dynamic loads and is suitable for fast storage and release of large amounts of energy.…”

“…According to the experimental and statistical data, the average fuel saving rate of the hybrid RTG crane was 73.9%. In February 2019, Bolonne et al [6] studied the energy management strategy of a hybrid power RTG crane consisting of a 200-kW variable-speed diesel generator (VSDG), a 55-kW lithium battery. and a 48.3-F SC.…”