Strategy And Application Study On Energy Management Of Proton Exchange Membrane Fuel Cell Hybrid Forklift

With the globalization of resource allocation, logistics industry has been developing rapidly, and certainly the demand for material carrying forklift is also increasing rapidly. In the face of environmental pollution, energy shortage and other problems, many enterprises attach great importance to the research and development of energy-saving, low-carbon material carrying forklifts. So the research and development of new energy forklift with cleanliness, no pollution, low noise and high energy efficiency is becoming a new development trend. With the significant advantages of low operating temperature, high power density, fast response and good stability, Proton exchange membrane fuel cell (PEMFC) is regarded as a highly promising new energy technology which is applicable to hybrid forklift power source.In this paper study the theories of global system solutions of the PEMFC hybrid forklift, optimal control method of air-cooled self-humidifying PEMFC, PEMFC cascaded DC/DC converter and hybrid energy management strategy, and designs hardware systems of the PEMFC hybrid forklift, constructs hybrid PEMFC sample forklift and verifies the hybrid system scheme and energy management strategy which this paper has proposed. The main research achievements are as follows:(1) According to the advantages and disadvantages of the hybrid power source and topology of the hybrid system, an overall system of the hybrid forklift is proposed. And clear graphic representations are shown in this paper, including a block diagram of the hybrid forklift system, a three-dimensional map of the hybrid system layout, a block diagram of the hybrid forklift’s functional unit and a schematic and three-dimensional map of the hydrogen gas supply system.(2) Based on the internal structure of air-cooled self-humidifying PEMFC and the essence of PEMFC’s optimal control, a test platform for the air-cooled self-humidifying PEMFC has been built, and the block diagram of the test platform is shown in this paper. With respect to the test platform, a start-stop control strategy and the relevant test software process is proposed, and the control software of the test platform is designed with Lab VIEW.(3)On the test platform, performance test for the air-cooled self-humidifying PEMFC stack of hybrid forklift is done, and then the stack temperature data are collected when the output voltage reachs the highest at the various test current points. In addition, the Polynomial curve fitting is used to fit the experimental data, and finally the relational expression between the stack’s output current Iout and optimal operating temperature Topt is acquired, which provides a calculation method of the reference temperature for the research of air-cooled self-humidifying PEMFC optimal temperature control strategy.(4) Based on theoretical analysis and tests of stack’s optimal temperature control implemented by fuzzy logic, PID, fuzzy-PID, adaptive fuzzy PID, this paper proposes a system temperature control method based on segmented prediction’s negative feedback (SPreNFC). With the experimental tests, the results show that this method can predict changes of the controlled object with the characteristics of fast response, short adjusting time and small overshoot, which makes up the shortages of common temperature control methods. Compared with other methods, the superiority of SPreNFC control method is obviously verified.(5) On the base of studying the topology structure and operating principles of four-switch Buck-Boost converter, the control strategy is proposed according to hybrid forklift system’s characteristics, and a four-switch Buck-Boost converter simulation model is built on the PSIM simulation platform. The validity and practicability of the proposed control strategy is verified through simulation, which lays a theoretical foundation for the hardware design of cascaded DC/DC converter.(6) For the sake of preventing PEMFC damage and ensuring stable operation of PEMFC system and prolonging its life, this paper presents a current following control strategy and an improved energy management control strategy, and builds a hybrid energy management simulation test platform. The test results show that the proposed current following energy management control strategy can achieve basicly a reasonable distribution of hybrid energy sources, effectively restrain the generation of peak current when the load power changes suddenly. Meanwhile, it makes PEMFC output current smooth and keeps the hybrid system operate stably and safely, and not only improves the reliability and practicality of the system, but also prolongs the PEMFC’s life.(7)Designing PEMFC-battery hybrid system hardware, and constructing PEMFC hybrid sample forklift. Using Visual C++ multi-thread technology, this paper designs the remote monitoring terminal program and conducts a simulation performance test for each hardware unit. The test results indicate that the function and performance of each hardware unit is excellent enough to meet the design requirements of PEMFC hybrid system. The actual operating results of the sample forklift turn out that the hybrid energy management control strategy is practical and effective, and performance of the hybrid sample forklift is superior, and each hybrid power source can work properly, with a high practical and popularized value.