Description

The fuel cell generation system is shown in Figure 1. The FCGS features a fuel cell that is connected to an inverter via a boost DC-DC converter. The fuel cell is a custom library from HYPERSIM. The boost converter maintains and steps up the DC voltage from the fuel cell to the DC point of connection with the inverter. The inverter is a three-phase two-level bridge of gate turn-off thyristor (GTO) with antiparallel diode. The inverter’s function is to maintain and regulate the DC link voltage and the reactive power at their respective commanded values at the point of common coupling (PCC). A RL choke filter is used to connect the inverter to the grid. The choke filter must be designed to limit the total harmonic distortion of the PVGS current injected into the grid at the point of common coupling (PCC).

The FCGS must be connected to an external step up transformer to the grid. It is recommended to use a star-delta transformer with a base power of 1.2 times the nominal power of the FCGS.

Figure 1 FCGS components schematic

Table of Contents

Mask and Parameters

System Parameters

Name	Description	Unit

Name	Description	Unit
Nominal Power - Sg	Nominal power of the FCGS	VA
Nominal Voltage - Vp	Nominal AC voltage of the FCGS	V
Nominal Frequency - f	Nominal frequency of the FCGS	Hz
Nominal DC Link Voltage - Vdc	Nominal DC voltage maintained at the DC link capacitor.	V
DC link Inductance - Ldc	DC link inductance.	H
DC link Capacitor - Cdc	DC link capacitor	F
Filter Resistance – Rgs	Filter resistance at the AC side.	Ω
Filter Inductance – Lgs	Filter inductance at the AC side	H
Switching frequency - Fsw	Switching frequency of the PWM that control the gating pulse signals of the inverter.	Hz
Boost Converter
Parasitic resistance- Rfc	Parasitic resistance of the boost inducatance	Ω
Input capacitance - Cfc	Input capacitance of the boost converter	F
Boost inductance - Lfc	Boost inductance	H
Inverter - GTO with Antiparallel Diode
Vmin	Forward voltage drop	V
Ropen	Open state resistance	Ω
Rclose	Close state resistance	Ω
Rsnubber	Resistance of the RC snubber branch in parallel with the valve	F
Csnubber	Capacitance of the RC snubber branch in parallel with the valve	Ω
Precision valve model	Enabling the precision valve disables the iteration for all nonlinear components in the same task	-

Control Loops Parameters

Name	Description	Unit

Name	Description	Unit
Active Power Regulator
KpP	Proportional gain PI controller for active power regulator.	-
KiP	Integral gain PI controller for active power regulator.	-
Reactive Power Regulator
KpQ	Proportional gain PI controller for reactive power regulator.	-
KiQ	Integral gain PI controller for reactive power regulator.	-
Current Regulator
KpI	Proportional gain PI controller for current regulator.	-
KiI	Integral gain PI controller for current regulator.	-
DC Regulator
KpVDC	Proportional gain of VDC Regulator	-
KiVDC	Integral gain of VDC Regulator	-
Fuel Cell Current Regulator
KpFC	Proportional gain of FC current regulator	-
KiFC	Integral gain of FC current regulator	-
Current Limit
CL	Current Limit	pu

Fuel Cell Parameters

Name	Description	Unit

Name	Description	Unit
Eoc	Open circuit voltage	V
V_1	Voltage at 1 Ampere	V
Vnom	Nominal voltage	V
Inom	Nominal current	A
Vmin	Minimum voltage	V
Imax	Maximum available current	A
tau	Response time	s

Stack Voltage vs Current

Ports, Inputs, Outputs and Signals Available for Monitoring

Ports

Name	Description

Name	Description
PCC	Network connection; supports 3-phase connection

Inputs

Name	Description	Units

Name	Description	Units
Qref	Reactive power reference.	pu
Pref	Active power reference.	pu
En	FCGS enabled. 1 – Enable, 0 – Disable.

Outputs

None

Sensors

Name	Description	Units

Name	Description	Units
Qref	Reactive power reference.	pu
Pref	Active power reference.	pu
En	FCGS enabled. 1 – Enable, 0 – Disable.	pu
Iabc0, Iabc1, Iabc2	Three-phase current through the choke filter.	A
Vdc	DC link voltage measured at the terminals of the DC capacitor	V
P	Active power absorbed/delivered by the BESS	pu
Q	Reactive power absorbed/delivered by the BESS	pu
V_FC	DC output voltage produced by the fuel cell	V
I_FC	DC output current produced by the fuel cell	A
Dout	Duty cycle control of the boost converter.	-

Modeling Details

The FCGS performs the control of its output currents in the dq reference frame. The structure of current regulator is shown in Figure 2. I_dq and V_dq are the grid currents and voltages, respectively, in the dq reference frame at the transformer primary while V_dqi are the inverter output voltages. The d axis current corresponds to the active power and the q axis current corresponds to the reactive power.

Figure 2 Current regulator

The FCGS synchronizes to the grid using a phase locked loop (PLL) block. The d axis current references are generated in order to regulate the DC link voltage at the reference value (1050V in this example). The DC link voltage regulator is shown in Figure 3.

Figure 3 DC link voltage regulator

The q axis current references are generated in order to follow the reactive power references provided to the inverter. The reactive power regulator is shown in Figure 4.

Figure 4 Reactive power regulator

The boost converter interfacing the fuel cell stack is operated with a duty cycle, d_boost, to control the current drawn from the fuel cell. The fuel cell current reference is generated by an active power regulator. Both the regulators are shown in Figure 5. The gain values for the current regulator should be slower than the response time of the fuel cell stack to ensure the control loop stability. The gains values of the active power regulator should be even slower than the fuel cell current regulator.

Figure 5 Active power regulator

References

S. N. M., O. Tremblay and L. A. Dessaint, "A generic fuel cell model for the simulation of fuel cell vehicles," 2009 IEEE Vehicle Power and Propulsion Conference, Dearborn, MI, 2009, pp. 1722-1729.

Fuel Cell Generation System (FCGS)