Zhiguo Lin School of Energy and Power Engineering, Wuhan University of Technology,
Wuhan 430063, P.R. China
Email: zglin@
Abstract—Traditional trailing suction hopper dredgers (TSHDs) are generally equipped with diesel engines as single power source. The diesel engines must be sized to cater for the maximum power demand, so they are significantly oversized most of the time. To solve this problem, an optimal retrofitting concept is proposed for matching main power equipments in hybrid propulsion system for a TSHD. The nondominated sorting genetic algorithm II (NSGA-II) is adopted to optimize the hybrid propulsion system design. Power equipments here include main engine, Variable Speed Drive (VSD), battery bank. The optimization is concerned with minimization of total installation weight and fuel consumption, also with limiting the value of State of Charge (SOC) by using graduated system of punishment. The different solutions are reflected in final Pareto front.
Fig. 1. Typical operation profile of trailing suction hopper dredger
II. RETROFITTING AND MODELING
A. Retrofitting “Tong Yuan” is originally equipped with two diesel engines. Each engine is connected to a controllable pitch propeller (CPP) and a shaft generator via two reduction gear boxes (GB).
In this paper, the authors retrofit a TSHD with hybrid propulsion concept, and optimize its power equipments by NSGA-II. Power equipments here include main engine, Variable Speed Drive (VSD), battery bank. The optimization is concerned with minimization of total installation weight and fuel consumption, also with limiting the value of State of Charge (SOC) by using graduated system of punishment. Section II presents TSHD's retrofitting and modeling. In Section III, the optimal algorithm and chromosome's structure are highlighted. The next two Sections present optimal results and conclusion.
When designing the HEV, there is a contradiction between fuel consumption and total weight or cost. Increasing the ESS size would decrease the fuel consumption, yet it would lead to an increased cost of size, weight and money. It’s a kind of typical multi-objective problem. The typical profiles of automotive and ships are different [2]. What is more, ships need more initial investment. However, the result may be worse than traditional configuration without appropriate design. So the optimal design method is very important when we design the hybrid propulsion ship. Nondominated sorting genetic algorithm II (NSGA-II), an effective multi-objective genetic algorithm, can solve it. The algorithm has been used in hybrid vehicle’s optimization design successfully [3-5]. E.A. Sciberras used NSGA-II in the optimal design for a hybrid motor yacht [2]. However it had no sufficient consideration of battery bank’s SOC, which only limited the value of SOC in energy management system, the SOC could not be guaranteed well for all solutions in final Pareto front. La Ta has done some research on influence factors for battery lifecycle. It was found that battery's SOC is one of key factors for its lifecycle [6]. The overdischarge (SOC in low level) of battery will shorten battery’s lifecycle.
Optimal Retrofitting of a Hybrid Propulsion System Using NSGA-II Algorithm for Trailing Suction Hopper Dredger
Keyi Zhan School of Energy and Power Engineering, Wuhan University of Technology,
978-1-4799-1857-7/15/$31.00 ©2015 IEEE
201
time spent percentage(%)
load profile
50 Leftengine
30
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0 0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100 load percentage(%)
Keywords—hybrid propulsion; trailing suction hopper dredger; NSGA-II; graduated system of punishment
I. INTRODUCTION
As a kind of self-propelled, self-loading and self-unloading seagoing or inland waterway vessels, trailing suction hopper dredgers (TSHDs) are widely utilized for dredging [1]. Traditional TSHDs are generally equipped with diesel engines as single power source. The diesel engines must be sized to cater for the maximum power demand, so they are significantly oversized most of time. Figure 1 shows a typical operational profile of six complete cycles from a TSHD, “Tongyuan”, which is owned by China Tianjin Waterway Bureau. It clearly shows that both engines are under-utilized for most of the time in the mission profile and both engines operate at high load (70% of MCR or above) for not more than 2% of overall operation time. There are similar problems in traditional load vehicles, especially some vehicles in urban area. It needs to run and stop frequently and engine often works in low load profile with low fuel efficiency. However, in a Hybrid Electric Vehicle (HEV), a VSD can get power supply from Energy Storage System (ESS) or act as a generator to