Abstract
This paper proposes a high-efficiency and compact fuel cell−battery hybrid power system without DC/DC converters. Generally, fuel cells supply power to charge lithium batteries or loads using DC/DC converters. The disadvantages of a DC/DC converter are its complex design, poor efficiency, and large volume. Therefore, improvements in the volume, weight, and efficiency are the main objectives of the proposed topology, which is suitable for stable operation in power equipment. This paper proposes a novel topology without DC/DC converters for a fuel cell−battery hybrid forklift system and analyzes, discusses, and verifies it with experimental measurements. Additionally, the proposed topology uses an average charging method to charge the Li-ion battery. The dynamic response of fuel cells is slower than that of Li-ion batteries. By properly configuring the voltages of a fuel cell and a lithium battery, we propose a hybrid system that can maintain a stable output and high efficiency in different operating modes without DC/DC converters. Detailed efficiency calculations and comparisons reveal that the method proposed in this paper achieves an efficiency increase of 5.36% compared with traditional approaches, while maintaining a set charging current. The proposed topology and charging method are verified with experiments on a 10 kW fuel cell−battery system, and the results indicate that the proposed method without DC/DC converters is more suitable for hybrid applications than traditional methods. The proposed system achieves optimal efficiency of 98.27%, surpassing the performance of a traditional hybrid system employing regulated DC/DC converters. Additionally, the system incorporates a mechanism to achieve constant current control, ensuring precise control over the desired charging current. The error in the desired charging current, determined through the average charging method, is 5%.