Fuel stack technology has emerged as a good alternative to conventional energy sources because it addresses important challenges such as high cost, limited long-term sustainability, and harmful emissions. Fuel stacks convert chemical energy into electrical energy by the electrochemical process which is cleaner and more efficient than combustion or any other conventional process. Fuel stacks are differentiated on the basis of electrolytes used, some commonly used fuel cells are Proton Exchange Membrane Fuel Cells (PEMFCs), Alkaline Fuel Cells (AFCs), Direct Methanol Fuel Cells (DMFCs), Phosphoric Acid Fuel Cells (PAFCs).

The Proton Exchange Membrane Fuel Stack (PEMFS) stands out for its suitability in automotive and portable power applications. It operates by converting chemical energy from hydrogen and oxygen into electrical energy, the process begins at the anode, where hydrogen gas is split into protons and electrons. The protons pass through the proton exchange membrane, while the electrons travel through an external circuit, generating electricity. At the cathode, the protons, electrons, and oxygen combine to form water, which is the only byproduct of this clean energy process.  Fuel cells are advantageous because they generate electricity with high efficiency and have low emissions.  

Overcoming Challenges and Enhancing Efficiency in Proton Exchange Membrane Fuel Cells (PEMFCs)

The traditional fuel cells face certain limitations as most fuel cells require higher operating temperatures and often involve complex and expensive materials. Also, the electrodes face high corrosion and due to this, the components tend to break. Subsequently, the system generates less power and takes more time to function. Proton Exchange Membrane Fuel Cells (PEMFCs) stand out because they operate at lower temperatures, have high energy density, and provide rapid system response, making them ideal for automotive use. Furthermore, the use of solid electrolytes helps to reduce corrosion which is a major problem in any other fuel cell. The polymer electrolyte membrane ensures fewer electrolyte-related issues which gives a more stable and reliable system.

Despite these advantages, PEMFS does have some limitations. A major disadvantage is that the PEMFS generates voltage in a non-linear fashion which affects the efficiency of power conversion. Also, they operate at a lower temperature range, this restriction affects the overall energy output and efficiency in environments where higher operating temperatures would be beneficial. To harness the full potential of PEMFS, an advanced power conversion and control strategy is essential. This is necessary to overcome the irregular voltage output and to ensure that the system operates efficiently by extracting maximum power from the fuel stack under varying conditions.

MPPT Technology Compliments to Improve PEMFS

To overcome the challenges of PEMFS a Maximum Power Point Tracking (MPPT) controller is used, which dynamically adjusts the operating point of the fuel stack to ensure that the system operates at its optimal power output, without operating at the optimal point the fuel cell system would suffer from inefficiencies, leading to energy losses, reduced overall performance, and a lower power output than its potential.

P&O and IC are two majorly used MPPT techniques. In the P&O (Perturb and Observe) algorithm the operating voltage of the fuel stack is changed and the resulting change in power is observed, if an increase in power is observed, the system continues adjusting in the same direction, but if a decrease in power is detected, the system reverses the direction of the perturbation. This algorithm is very simple in design, has good reliability of the technique, and is easy to handle. However, the disadvantages of this controller are that there is more distortion of fuel stack supply voltage and a low level of MPP accuracy.

The IC technology measures the derivative of the power concerning the voltage (dP/dV) to determine whether the system is operating at the MPP. When this value equals zero, the system is at its maximum power point. Unlike P&O, which relies on continuous perturbations, the IC method tracks changes in the output directly and adjusts the operating point accordingly. The cost of this network is more as compared to the P&O conventional controller. These conventional methods often result in suboptimal performance, with slower response times and reduced tracking accuracy.

Figure 1: PSO based MPPT Controller

To tackle these limitations researchers came up with a new innovative hybrid approach that combines Particle Swarm Optimization (PSO) with Adaptive Neuro-Fuzzy Inference System (ANFIS) algorithms. PSO excels at optimising complex, nonlinear systems like Proton Exchange Membrane Fuel Stacks (PEMFS) due to its ability to quickly and accurately locate the global maximum power point. ANFIS complements this by integrating the learning capabilities of neural networks with the reasoning abilities of fuzzy logic systems.  

The PSO-ANFIS controller can identify the exact Maximum Power Point (MPP) of the PEMFS with remarkable precision, even when faced with rapid fluctuations in environmental conditions such as temperature and load demand. This accuracy is crucial for maintaining the efficiency of the fuel cell system, ensuring that it operates at its optimal level. The PSO-ANFIS hybrid MPPT controller is a huge advancement in the fuel stack technology; this method not only just increases the efficiency of fuel cells but paves a broader path for using hydrogen-powered vehicles and renewable energy systems.

Figure 2: Adaptive Neuro-Fuzzy Inference System Algorithms

Using DC-DC Converters to Stabilise Load Input

The PEMFS gives a wide range of voltage in output, here the DC-DC converters are used to step up or step down voltage according to the requirement of the load. As normal converters struggle with these fluctuations, researchers introduced a novel DC-DC converter that addresses these issues by offering a higher voltage transformation ratio, lower voltage stress across the switching devices, and wider voltage gain. This ensures a more stable and efficient power supply to the vehicle's motor, even when the fuel stack voltage fluctuates.

The design and selection of inductive components are critical for maintaining a consistent voltage supply to the fuel stack. The inductors are responsible for storing energy during the switching phases, and their sizing must be carefully calculated to satisfy the requirements for uniform voltage output. The voltage distribution law is applied to determine the static potential variations of all capacitive and inductive components, guiding the selection process for these elements.

Figure 3: PSO-ANFIS MPPT controller integrated with a wide range DC-DC converter

The PSO-ANFIS MPPT controller integrated with a wide range DC-DC converter brings significant advantages to fuel stack applications. This integration allows efficient conversion and minimal energy loss improving overall system performance. The system is more reliable as it can maintain stable performance across a broad range of environmental and load variations. By simplifying the power conversion circuitry and reducing the number of complex components, the system lowers both development and long-term maintenance costs. The ability of the system to be compact and more efficient makes it more user-friendly and cost-friendly too.