Fuel cell system multiple stage voltage control method and apparatus

A fuel cell system, comprising:

• a number of fuel cells forming a fuel cell stack;
• a number of battery cells forming a battery;
• a series pass element;
• a blocking diode electrically coupled between the fuel cell stack and the series pass element;
• a regulating circuit for regulating current through the series pass element in proportion to at least a greater of a difference between a battery charging current and a battery charging current limit, a difference between a battery voltage and a battery voltage limit, and a difference between a stack current and a stack current limit;
• a reactant delivery system for delivering reactant to the fuel cells, the reactant delivery system including at least a first flow regulator adjustable to control a partial pressure in a flow of a reactant to at least some of the fuel cells;
• and
• a control circuit coupled to receive signals corresponding to a voltage across the series pass element and to provide a control signal to at least the first control element mathematically related to a voltage difference across the series pass element.

A circuit for a fuel cell system having a fuel cell stack and a battery, the control circuit comprising:

• a series pass element electrically coupleable between at least a portion of the fuel cell stack and a portion of the battery;
• a regulating circuit for regulating current through the series pass element in response to a greater of a battery charging current error, a battery voltage error and a stack current error;
• and
• a control circuit coupled to receive signals corresponding to a voltage on an input side and an output side of the series pass element and configured to determine a deviation of a voltage difference across the series pass element from a desired operational condition based on the received signals and to produce a control signal based on the determined deviation.

A circuit for a fuel cell system, comprising:

• a series pass element;
• a blocking diode electrically coupled in series with the series pass element;
• a regulating circuit coupled to the series pass element to regulate a current through the series pass element in proportion to at least a greater of a difference between a battery charging current and a battery charging current limit, a difference between a battery voltage and a battery voltage limit, and a difference between a stack current and a stack current limit;
• and
• a control circuit coupled to receive signals corresponding to a voltage across the battery and to provide a control signal mathematically related to a difference between the voltage across the battery and a defined desired voltage across the battery.

A circuit for a fuel cell system, comprising:

• a battery charging current sensor;
• a battery charging current error integrator having a first input coupled to the battery charging current sensor to receive a battery charging current signal proportional to a battery charging current, a second input coupled to receive a battery charging current limit signal proportional to a battery charging current limit, and an output to supply a battery current error signal proportional to a difference between the battery charging current and the battery charging current limit;
• a battery voltage sensor;
• a battery voltage error integrator having a first input coupled to the battery voltage sensor to receive a battery voltage signal proportional to a battery voltage, a second input coupled to receive a battery voltage limit signal proportional to a battery voltage limit, and an output to supply a battery voltage error signal proportional to a difference between the battery voltage and the battery voltage limit;
• a stack current sensor;
• a stack current error integrator having a first input coupled to the stack current sensor to receive a stack current signal proportional to a stack current, a second input coupled to receive a stack current limit signal proportional to a stack current limit, and an output to supply a stack current error signal proportional to a difference between the stack current and the stack current limit;
• an OR circuit coupled to the output of each of the battery current error integrator, the battery voltage error integrator and the stack current error integrator;
• a series pass element having a pair of terminals for selectively providing a current path and a control terminal coupled to the OR circuit for regulating current through the current path in proportion to a greater of the battery current error signal, the battery voltage error signal and the stack current error signal;
• and
• a control circuit coupled to receive signals corresponding to a voltage on an input side and an output side of the series pass element and configured to determine a deviation of a voltage difference across the series pass element from a desired operational condition based on the received signals and to produce a control signal based on the determined deviation.

A circuit for a fuel cell system, comprising:

• means for determining a greater of a difference between a battery charging current and a battery charging current limit, a difference between a battery voltage and a battery voltage limit, and a difference between a stack current and a stack current limit;
• series pass regulating means for regulating a flow of stack current through a blocking diode in proportion to the determined greater difference;
• means for determining a difference between a voltage difference across the series pass regulating means and a desired a desired operational condition of the series pass regulating means;
• and
• means for controlling a partial pressure of at least one reactant flow in proportion to the determined difference between the voltage difference across the series pass regulating means and the desired operational condition of the series pass regulating means.

A method of operating a fuel cell system, comprising:

• supplying current at a number of output terminals from at least one of a fuel cell stack and a battery electrically coupled in parallel with the fuel cell stack;
• in a first stage, regulating a current through a series pass element in proportion to at least a greater of a difference between a battery charging current and a battery charging current limit, a difference between a battery voltage and a battery voltage limit, and a difference between the stack current and the stack current limit;
• and
• in a second stage, adjusting a partial pressure of a reactant flow to at least a portion of the fuel cell stack to maintain a series pass element at a desired saturation level.

A method of operating in a fuel cell system, the method comprising:

• determining a battery charging current error;
• determining a battery voltage error;
• determining a stack current error;
• regulating current through a series pass element in response to a greater of the battery charging current error, the battery voltage error and the stack current error;
• determining a voltage difference across the series pass element;
• determining an amount of deviation of the determined voltage difference from a desired operational condition of the series pass element;
• and
• for at least one reactant flow to at least a portion of the fuel cell stack, adjusting a partial pressure of the reactant flow based on the determined amount of deviation.

A method of operating in a fuel cell system, the method comprising:

• determining a difference between a battery charging current and a battery charging current limit;
• determining a difference between a battery voltage and a battery voltage limit;
• determining a difference between a stack current and a stack current limit;
• regulating a current through a series pass element in proportion to at least a greater of the difference between the battery charging current and the battery charging current limit, the difference between the battery voltage and the battery voltage limit, and the difference between the stack current and the stack current limit;
• determining a voltage difference across the series pass element;
• determining an amount of deviation of the determined voltage difference from a desired operational condition of the series pass element;
• and
• for at least one reactant flow to at least a portion of the fuel cell stack, adjusting a partial pressure of the reactant flow based on the determined amount of deviation.

A fuel cell system, comprising:

• a voltage bus;
• a first fuel cell stack electrically couplable across the voltage bus;
• a first battery electrically couplable across the voltage bus;
• a first series pass element electrically coupled in series on the voltage bus between at least a portion of the first fuel cell stack and a portion of the first battery;
• a first regulating circuit for regulating current through the first series pass element in response to a greater of a battery charging current error, a battery voltage error and a stack current error;
• a first reactant delivery system for delivering reactant to the first fuel cell stack, the reactant delivery system including at least a first control element adjustable to control a partial pressure in a flow of a reactant to at least some of the fuel cells of the first fuel cell stack;
• a first control circuit coupled to receive signals corresponding to a voltage on an input side and a voltage on an output side of the first series pass element and configured to determine a deviation of a voltage difference across the first series pass element from a desired operational condition based on the received signals, the first control circuit further coupled to control the at least first control element based on the determined deviation;
• a second fuel cell stack electrically couplable across the voltage bus;
• a second battery electrically couplable across the voltage bus;
• a second series pass element electrically coupled in series on the voltage bus between at least a portion of the second fuel cell stack and a portion of the second battery;
• a second regulating circuit for regulating current through the second series pass element in response to a greater of a battery charging current error, a battery voltage error and a stack current error;
• a second reactant delivery system for delivering reactant to the second fuel cell stack, the reactant delivery system including at least a second control element adjustable to control a partial pressure in a flow of a reactant to at least some of the fuel cells of the second fuel cell stack;
• and
• a second control circuit coupled to receive signals corresponding to a voltage on an input side and a voltage on an output side of the second series pass element and configured to determine a deviation of a voltage difference across the second series pass element from a desired operational condition based on the received signals, the second control circuit further coupled to control the at least second control element based on the determined deviation.

A fuel cell system combination, comprising:

• a voltage bus;
• a first fuel cell system having a first fuel cell stack and a first battery electrically coupled in parallel across the voltage bus;
• and
• a second fuel cell system having a second fuel cell stack and a second battery electrically coupled in parallel across the voltage bus.