Energy Management System of Fuel Cell Hybrid Power Supply
1. 12.5 kW (peak), 30-60 V PEM (proton exchange membrane) fuel cell power module (FCPM), nominal power 10 kW.
2. One 48 V, 40 Ah, Li-ion battery system
3. 291.6 V, 15.6 F supercapacitor system (six 48.6v batteries connected in series)
4. 12.5 kW fuel cell DC/DC boost converter with stable output voltage and input current limit.
5. Two DC/DC converters for discharging (4 kW boost converter) and charging (1.2 kW buck converter) of the battery system. These converters also regulate the output voltage through current limiting. Often, a single bidirectional DC/DC converter can also be used to reduce the weight of the power system.
6. 15 kVA, 270 V DC input, 200 V AC, 400 Hz inverter system.
Three-phase AC load with variable apparent power and power factor to simulate MEA emergency load profile.
7. A 15 kW protection resistor to avoid overcharging of the supercapacitor and battery system.
An energy management system that allocates power among energy sources based on a given energy management policy. Five types of energy management strategies are implemented, they are:
State Machine Control Strategy
Classic PI control strategy
Frequency Decoupling and State Machine Control Strategy
Equivalent Consumption Minimization Strategy (ECMS)
External Energy Maximization Strategy (EEMS)
Demonstration
This demonstration demonstrates the performance of a fuel cell hybrid emergency power system in a five-minute emergency landing scenario. In this case, the fuel cell hybrid system provides base load during the following events:
Immediately upon loss of the main generator (this is usually assumed by the avionics and APU battery systems until the RAT/ADG is fully deployed).
The emergency hydraulic pump starts.
Movement of flaps/slats and landing gear.
Taxiing and passenger evacuation (when the RAT/ADG becomes unavailable, the avionics and APU battery systems are usually also assumed).
Depending on the type of energy management strategy selected, the energy management system controls the power of each energy device via the reference signals (output voltage and maximum current) of the fuel cell and battery DC/DC converters. Double-click the Energy Management System module and select the state machine control strategy. Start the simulation. Double-click the measurement block. Opens the power range (displaying the power distribution related to the 270 V DC bus) as well as the fuel cell, battery, supercapacitor and load ranges. Here's an explanation of what would happen in this simulated emergency landing scenario:
At t = 0 s, the base load is powered by the main generator and the fuel cell hybrid system is turned on to prepare for the unlikely emergency landing situation.
At t = 5 s, the fuel cell starts charging the battery at its optimal power (approximately 1 kW).
At t = 40 seconds, all generators are lost. The fuel cell hybrid system takes over the necessary load. The additional load power required at this time is provided instantly by the supercapacitor due to its fast dynamics, while the fuel cell power increases slowly.
At t = 45 s, the supercapacitor discharges below the desired DC bus voltage (270 V) and the battery starts supplying power to regulate the bus voltage back to 270 V.
At t = 48.5 seconds, the DC bus or supercapacitor voltage reaches 270 V and the battery power slowly decreases to zero. The fuel cell provides the total load power and continues to charge the supercapacitor.
At t = 60 s, the emergency hydraulic pump is started, the supercapacitor provides additional transient load power, and the fuel cell power slowly increases.
At t = 61.5 seconds, the battery comes online to regulate the DC bus voltage to 270 V and assist the fuel cell by providing the additional load power required.
At t = 70 s, the fuel cell reaches its maximum power (FCPM power is limited to 9 kW due to its DC/DC converter input voltage range) and additional load power is provided by the battery.
At t = 110 s, the battery also reaches its maximum power (4 kW) and the supercapacitor provides additional load power.
At t = 125 seconds, the load power drops below the maximum power of the fuel cell. Due to slow fuel cell kinetics, additional fuel cell power is transferred to the supercapacitor during transients.
At t = 126 seconds, the DC bus voltage reaches 270 V and the battery charge drops to zero.
At t = 130 seconds, the second emergency hydraulic pump is turned on and the behavior of the fuel cell hybrid system is similar to that when the first hydraulic pump is turned on.
At t = 170 seconds, the load power drops below the fuel cell maximum power and the additional fuel cell power is transferred to the battery and supercapacitor.
At t = 180 s, there is a sudden increase in load due to the movement of the flaps/slats and landing gear. The supercapacitor again responds quickly by providing additional power to the load.
At t = 185 seconds, the battery discharges to regulate the DC bus voltage and help the fuel cell obtain the required additional load power.
At t = 235 s, the aircraft has landed and the load power suddenly drops. Additional fuel cell energy is stored in batteries and supercapacitors.
At t = 250 seconds, the aircraft is taxiing and the fuel cell is providing almost the total load power required.
At t = 330 seconds, the passengers have been evacuated and the load power has dropped to zero. The fuel cell slowly reduces its power to optimal power and charges the battery.
