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Fuel Cell Generation System (FCGS)

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

NameDescriptionUnit

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.

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- RfcParasitic resistance of the boost inducatance
Input capacitance - CfcInput capacitance of the boost converterF
Boost inductance - LfcBoost inductanceH

Inverter - GTO with Antiparallel Diode

VminForward voltage dropV
RopenOpen state resistance
RcloseClose state resistance
RsnubberResistance of the RC snubber branch in parallel with the valveF
CsnubberCapacitance of the RC snubber branch in parallel with the valve
Precision valve modelEnabling the precision valve disables the iteration for all nonlinear components in the same task-

Control Loops Parameters



NameDescriptionUnit

Active Power Regulator

KpPProportional gain PI controller for active power regulator.-
KiPIntegral gain PI controller for active power regulator.-
Reactive Power Regulator
KpQProportional gain PI controller for reactive power regulator.-
KiQIntegral gain PI controller for reactive power regulator.-
Current Regulator
KpIProportional gain PI controller for current regulator.-
KiIIntegral gain PI controller for current regulator.-
DC Regulator
KpVDCProportional gain of VDC Regulator-
KiVDCIntegral gain of VDC Regulator-
Fuel Cell Current Regulator
KpFCProportional gain of FC current regulator-
KiFCIntegral gain of FC current regulator-
Current Limit
CLCurrent Limitpu

Fuel Cell Parameters

NameDescriptionUnit

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


NameDescription
PCCNetwork connection; supports 3-phase connection

Inputs


NameDescriptionUnits
Qref

Reactive power reference.

pu
Pref

Active power reference.

pu
EnFCGS enabled. 1 – Enable, 0 – Disable.

Outputs

None

Sensors


NameDescriptionUnits
Qref

Reactive power reference.

pu
Pref

Active power reference.

pu
EnFCGS 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 2Idq and Vdq are the grid currents and voltages, respectively, in the dq reference frame at the transformer primary while Vdqi 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, dboost, 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

  1. 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.

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