16kW hybrid power pack
The pp16 power pack is a triple hybrid power source designed and built to drive an electric forklift as a demonstration platform within the WorkingPEM research project (see history for more info about the project).
The triple hybrid configuration consists on:
- A PEM fuell cell providing the main power
- Battery to store/feed the excess/lack of energy from the fuel cell during low/high load states. Lead-acid battery was considered a realistic option for a forklift because of the weight, tolerance of wide range of voltages and low cost.
- Ultracapacitors to deal with the heavy and fast variation of electric load typical of of heavy loads manouvering applications and storing the regenerated braking energy.
Triple hybrid topology
The benefits of a hybrid system compared to purely fuel cell based power source, are that it allows the size of the expensive fuel cell component to be smaller and leads to the fuel cell being operated closer to constant load conditions, while the other energy storage system(s) provide the peak load. The main motivation of the tri-hybrid configuration shown above is the assumption that neither the lead-acid battery nor the fuel cell can handle very high discharge rates well, especially if maximum lifetime is pursued (as is the case with industrial vehicles) and thus, the ultracapacitor is placed in parallel with them to "shave" the load peaks.
In this page you will find mainly information about the electronics and software of the control system. For details about the fuel cell itself (BoP, experiments and results, etc), read the article Development of integrated fuel cell hybrid power source for electric forklift, published in Journal of Power Sources
The Nedstack P8 stack, that was used in both the 8kW and 16kW systems, is a low pressure PEMFC stack, meaning that only very slight pressurization of anode and cathode subsystems is preferred. Liquid cooling is used to transfer excess heat out of the stack and also to stabilize internal temperature differences inside it. A simple overview of the BoP system structure is shown in the figure below.
BoP (Balance-of-Plant) of 16kW PEMFC system
Main features of the fuel cell system in question are the low pressure operation, enabling the use of by-pass type blower common in many appliances (like. for example, vacuum cleaners) today. The hydrogen supply is a low pressure metal-hydride storage from which the fuel is fed in to the PEMFC stack anode, trying to maintain constant pressure in the system by means of a regulator. Temperature management system utilizes the synergy of the endothermic metal-hydride storage discharge reaction and the exothermic fuel cell reaction by coupling the two components together in a common coolant loop.
The Ethernut3 was chosen as the microcontroller board. Because of the different BoP arrangement, the number of required I/O channels increased compared to the 8kW power source, and a new version of the instrumentation board was developed, the IB3. Among other things, it added a second CAN bus to the system for possible connection to the machine that the power source would be powering.
The control software was implemented as a user application layer using the NutDAC system, and was divided in two parts:
The microcontroller side, with the control loops for autonomous operation implemented as state machines (see Control Strategies for details). It consists of a daemon-like automated control component which, once initiated, handles the necessary control tasks without direct user intervention. Other components in the software include the CAN drivers for communication with the CVM units and an I/O spoofing "emulator" which at it's current state can be used mainly for simple testing of the control software and overriding some of the system checks and safety features.
The source code is available as a NutDAC_Micro dependent project, codenamed pp16. You will also need the ib3tester containing the drivers of the IB3. Simply copy them to the same directory.
The PC side, with a GUI to start/stop the autonomous control and controls to operate the system manually, together with tools to facilitate calibration and data storage for posterior analysis. The source code is available as a NutDAC_GUI dependent project, codenamed pp16_gui. Here you can see the resulting GUI