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Power Conversion and Control for Fuel Cell Systems in Transportation 313

fuel cells, there is intense competition around the world to develop FCVs and fuel cell–based power
generation systems.

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Appendix 12A: Fuel Cell MPPT MATLAB Example
12A.1 Description

MATLAB simulation of maximum power extraction of fuel cells using boost converter with per-
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turb and optimize (P&O) MPPT control algorithm

12A.2 Explanation
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The MATLAB Simulink diagram of the power circuit shown in Figure 12.17 consists of an input
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fuel cell model, a boost converter, an output DC bus with load, and an MPPT controller. Explanation
of each block is given below. The simulation diagram is shown in Figure 12.20.
1. Fuel cell model: The inputs to the fuel cell block are temperature and fuel flow, and the
output is generated electric power.
All the constant parameters are defined inside the function block. Open-circuit voltage of
33.5 V and short-circuit current of 8.21 A have been updated inside the model to produce
240 W. Series and parallel combinations of cells are represented as Ns (9) and Np (6),
respectively. These parameters can be changed to replicate any module.
2. Boost converter: Boost converter with input and output capacitor has been developed in
the MATLAB Simulink with SimPowersystem tools. The converter is designed for 500
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W with the following parameters. These design parameters are defined inside the m-file
paramBoostMPPT.m:
Fs = 100e3; % Switching frequency 100 kHz
gV = 48; % Output Voltage
o
Tsamp = 1/(Fs*10); % Sampling time of simulation 100 times of switching frequency
Prated = 500; % Output Power 500 W
gV = 30; % Input Voltage
in
CurRIP= 5/100; % Input Current Ripple
gVolRIP= 5/100; % Output Voltage Ripple
Po= Prated/100 * 100; % 100 means full load
MinLoad = 1/100 * 10; % 10% load is the minimum
C = 50e-6; % 50 uF
in
3. DC bus: In order to maintain constant voltage at the output side, a voltage source of 48 V
is connected in parallel with load.
4. MPPT control: The purpose of the MPPT control is to track the maximum power by vary-
ing the duty cycle of the boost converter. The concept of P&O method has been utilized in
the MPPT control. The algorithm works based on modifying (increasing or decreasing) the
operating voltage until maximum power is reached. A simple flowchart of P&O is shown
in Figure 12.21.

Under steady-state operation, the boost converter output V is given by V = V /(1−D) or V =
o
o
in
in
V (1−D). The relationship between change in duty cycle with respect to change in voltage for
o
boost converter can be derived as delD = −delV /V . A tolerance limit of ±delP (change in power)
in
o
is set in order to stop at a certain value of duty cycle. A sampling time tmppt should be decided
for MPPT algorithm such that the boost converter duty cycle is modified only during steady-state
operation of the converter.