1. Introduction
In the past few decades, fossil fuels have been widely used as the power source of ordinary internal combustion engine, which has caused lots of negative effects, such as the gradual depletion of oil resources, the deepening of the global energy crisis, the aggravation of air pollution, and the rise of global temperature. Therefore, a series of new energy vehicles emerge at a historic moment. Many studies have been done on fuel cell vehicles for their convenient, efficient, and clean energy utilization.
A fuel cell is the main power source, and the battery or ultra-capacitor is the auxiliary power source to provide power for the fuel cell hybrid vehicle (FCHV) when FCHV is in operation. This hybrid power distribution method has been widely used in FCHV. Therefore, the hybrid power distribution mode of FCHV has been the focus of a lot of research, in which the energy management strategy of controlling the fuel cell system and energy storage system are their key topics. In this research, different energy management strategies are used to improve the economy of FCHV and optimize their dynamic performance.
In recent years, a variety of energy management strategies have been applied to hybrid vehicles [
1,
2,
3,
4,
5,
6,
7,
8,
9,
10,
11,
12,
13,
14,
15,
16]. Guenther et al. [
1] used the method of sampling optimizations to explore the feasibility of decreasing the cost of fuel cell vehicle (FCV). Montazeri-gh et al. [
2] set the rule to improve fuel economy based on multiple input variables. Djerioui et al. [
3] proposed Grey Wolf Optimizer (GWO) for the hybrid power system to address the management of fuel cell and supercapacitor hybrid power source. Hong [
4] proposed an energy management strategy based on dynamic following coefficient (ECMS_DMC) for FCHV, which maintained the efficiency of the fuel cell hybrid power system above 44% and extended the battery life. Chen et al. [
5] proposed an online, efficient, and practical rule-based energy strategy to manage the energy distribution of a hybrid fuel cell/battery vehicle. Carignano et al. [
6] proposed a new energy management strategy based on the estimation of short-term energy demand and aiming at maintaining the state of energy of the supercapacitor between two limits. Xu et al. [
7] provided an adaptive control strategy for fuel cell and battery hybrid bus based on the equivalent minimum consumption strategy, so as to satisfy complex urban conditions. Bendjedia et al. [
8] presented a classic method based on frequency separation. Aouzellag et al. [
9] presented a novel control strategy that ultra-capacitor control power was realized indirectly through the direct current bus voltage regulation and an algorithm with filtering power vibrations was developed for fuel cell power demand. Lv et al. [
10] summarized the effectively influence of genetic algorithm to choose the optimized parameters and objects. The optimal control strategy increased the energy utilization efficiency and prolonged the life of the fuel cell. A real-time and approximately optimal energy management based on Pontryagin’s minimum principle (PMP) was proposed by Song [
11] et al., and it positively solved the problems of fuel economy and power source durability. Li [
12] et al. studied an energy management system based on Pontryagins’s Minimal Principle for FCHV. The simulation results under three driving cycle verified the effectiveness of the presented strategy. Aiming at improving power performance and fuel economy a hierarchical energy management system based on low-pass filter and equivalent consumption minimization (ECMS) was developed by Fu [
13] et al. To reduce the hydrogen consumption and battery contribution Odeim et al. [
14] proposed a real-time strategy based on an offline algorithm. Hu et al. [
15] employed multi-objective optimization strategy to improve the fuel economy and system durability. Zhang et al. [
16] presented a multi-mode method based on equivalent consumption minimization strategy to decrease fuel consumption.
Compared with other control methods, fuzzy logic control (FLC) strategies were adopted to optimize vehicle performances based on its inherent advantages [
17]. Li et al. [
18] presented the FLC strategy for FCHV to optimize the energy management system with both dynamic and economic performance under different cycle conditions. Zhang et al. [
19] established the FLC strategy for a fuel cell and battery hybrid locomotive. An adaptive controller based on FLC was proposed for FCHV, so that fuel cell output can reach the load power more smoothly [
20]. In order to select the optimal fuzzy controller, genetic algorithm was adopted to adjust the control parameters [
10,
21,
22]. Ahmadi et al. [
21] presented the FLC strategy and utilized genetic algorithm (GA) to adjust the control parameters. Fu et al. [
22] presented an optimized frequency decoupling energy management strategy that utilized the fuzzy logic control and adopted genetic algorithm to optimize the performance of the FCHV.
In this paper, the powertrain of the FCHV and selection of the power source are presented in the section of FCHV configuration and calculations. A fuzzy logic control (FLC) method is proposed to design appropriate energy management strategy, vehicle performance including fuel economy, efficiency of battery and fuel cell system, battery SOC, and battery life are analyzed. Further, a model of fuel cell and battery hybrid vehicle is developed and Chinese typical city driving cycle is added into ADVISOR platform. To comprehensively examine the proposed energy management system, four cycle conditions are selected to evaluate and analyze the FCHV performance.
5. Results and Discussion
In order to compare the indexes of acceleration tests, economy and grade, Chinese Typical City Driving Cycle is selected. The simulation results of PFC strategy and FLC strategy are compared and analyzed.
Table 5 compares the dynamic and economic performance of FCHV.
According to
Table 5, the dynamic and economic performance of PFC strategy and FLC strategy can satisfy the design requirements. From the perspective of dynamic performance, the maximum speed of FCHV using the FLC strategy can reach 157.3 km/h, slightly higher than that of the original PFC strategy. The acceleration time of 0–50 km/h and 0–100 km/h decreased by 9% and 17%, respectively. The maximum gradeability at 30 km/h was reduced by 8%. In view of the economic performance, hydrogen consumption and the equivalent oil consumption of FCHV utilizing FLC strategy is respectively 74.1 L/100 km and 5 L/100 km. Compared with the vehicle that uses PFC strategy, hydrogen consumption and the equivalent gasoline consumption reduces 6.9% and 9.1% respectively. Obviously, FCHV becomes more economical.
According to
Table 6, fuel economy, FCS/battery efficiency and
SOC are the main targets that should be studied. It’s obvious that the FLC for FCHV has lower hydrogen consumption and equivalent energy than PFC. Therefore, the proposed FLC strategy not only satisfies the requirement of FCHV, but also improves the economic performance. And the efficiency of FLC for FCHV is higher than that of PFC in terms of fuel cell system and battery. Moreover, as a significant index of FCHV, the SOC of the battery is more stable.
Comparison of SOC in two different strategies are shown in
Figure 4. It can be seen from the curve that fluctuation range of both strategies is in good charging and discharging area. In comparison, the variation range of SOC using PFC strategy is relatively larger, while utilizing FLC strategy is more stable and belongs to the type of shallow charge and shallow discharge, which effectively improves the battery life and decreases the cost of vehicle maintenance that is the most critical issue of people’s concern.
Figure 5 and
Figure 6 show the efficiency curves of charging and discharging components in different strategies. Through the comparison of working efficiency points, it can be clearly seen that the charging and discharging efficiency points of FLC strategy are more concentrated. As can be seen from
Table 6, efficiency of FCS and battery under FLC strategy is higher. Since the extremely high cost of FC, the improvement of efficiency is of great significance. Through a thorough comparison, the increase in economic performance and operating efficiency of FCHV indicates the priority of FLC strategy.
As shown in
Figure 7, when FLC strategy is utilized, the initial SOC of the battery is 0.7 and the battery can provide enough power for the motor during the startup. After a short time, the fuel cell comes into operation and charges the battery. Therefore, the working life of battery is improved and the external battery charger is not required. In order to ensure that the fuel cell can work in the efficient zone, fuel cell and battery rarely output the power together.
Figure 8 shows hydrogen consumption in four cycle conditions. It’s clear that the hydrogen consumption of FLC for FCHV is lower. Therefore, this strategy has a better performance in terms of fuel economy.
6. Conclusions
In this paper, the powertrain of an FCHV is designed and the parameter of the main components obtained. The simulation software ADVISOR is secondly developed and a Chinese typical city driving cycle is introduced. Since energy management strategy plays a vital role in vehicle performance, the FLC strategy and PFC strategy are designed for the studied FCHV.
Both PFC and the proposed FLC strategy can meet the requirement of dynamic performance of the studied FCHV. Moreover, fuel economy, efficiency of power supplies, battery SOC and battery life are some significant outcomes achieved by the FLC strategy. In four driving cycles, the FLC for FCHV has lower consumption and higher efficiency than that of the PFC strategy. Hence, in terms of economy and operating efficiency, the FLC strategy is better. Furthermore, the charging and discharging efficiency under the FLC strategy is more stable and the SOC under the FLC strategy is smoother than that of the PFC strategy. Therefore, the battery life can be extended and the cost of vehicle maintenance can be decreased. When FLC strategy is utilized, the battery can provide enough power for the motor during the startup and the fuel cell comes into operation and charges the battery after a short time. Since the battery is continuously charged during the driving cycles, there is no need to provide an external battery charger.
The FLC strategy is more suitable for the energy management strategy for fuel cell and battery hybrid vehicles. Research results and proposed FLC strategy can be referenced for further such researches.