Hybrid electrical power source combining stirling engine driven alternator with supplementing electrical energy storage

• US 7,701,075 B2
• Filed: 12/05/2008
• Issued: 04/20/2010
• Est. Priority Date: 12/05/2007
• Status: Expired due to Fees

• Current Assignee: Sunpower Corporation (Totalenergies Se)
• Original Assignee: Sunpower Corporation (Totalenergies Se)
• Inventors: Holliday, Ezekiel S.
• Primary Examiner(s): Patel; T C
• Assistant Examiner(s): Mohandesi; Iraj A
• Application Number:
  US12/328,981
• Publication Number:
  US 20090206667A1
• Time in Patent Office: 501 Days
• Field of Search: 290/40.C, 290/40.B, 290/1.R
• US Class Current: 290/40.00C
• CPC Class Codes: F02G 1/0435 the engine being of the free piston type
• CPC Class Codes: F02G 1/045 Controlling
• CPC Class Codes: F02G 2280/10 Linear generators
• CPC Class Codes: H02P 9/04 Control effected upon non-electric prime mover and dependent upon electric output value of the generator

Abstract

An electrical power source including a free-piston Stirling engine driving an alternator to supply power through a bus to a user load and controlled by an engine/alternator controller. A bidirectional DC/DC converter is connected between a battery and the bus. The stroke of the engine piston is modulated between a maximum and a minimum stroke to maintain the bus voltage at a design nominal bus voltage (V₁), and charge the battery if it is not charged, when and so long as the bus voltage does not fall below a design nominal bus voltage (V₁). The Stirling engine is operated at its maximum piston stroke, and the battery is charged if it is not charged, when the bus voltage is in the range between the design nominal bus voltage (V₁) and a design minimum battery charging bus voltage (V₂). The Stirling engine is operated at its maximum piston stroke and the battery is disconnected from the bus so it can not charge when the bus voltage is in the range between the design minimum battery charging bus voltage (V₂) and a design minimum bus voltage (V₃). The Stirling engine is operated at its maximum piston stroke and power is applied from the battery to the bus for maintaining the bus voltage at the design minimum bus voltage (V₃) when the power supplied from the alternator operating at its maximum stroke is less than the power demand of the load.

Claims

1. A method for operating an electrical power source, the power source having a free-piston Stirling engine including a piston driving a linear alternator connected through a rectifier to a bus to apply a voltage to the bus, the power source also having a battery, the method allowing the electrical power supplied from the power source to a load to, at times, exceed the maximum power that can be delivered from the free-piston Stirling engine driving the linear alternator, the method comprising:

(a) modulating the stroke of the engine piston between a maximum and a minimum stroke to maintain the bus voltage at a design nominal bus voltage (V₁) and charging the battery if it is not charged, when and so long as the bus voltage does not fall below the design nominal bus voltage (V₁);

(b) operating the Stirling engine at the maximum piston stroke and charging the battery if it is not charged when the bus voltage is in the range between the design nominal bus voltage (V₁) and a design minimum battery charging bus voltage (V₂) that is less than the design nominal bus voltage (V₁);

(c) operating the Stirling engine at the maximum piston stroke and disconnecting the battery so it can not charge when the bus voltage is in the range between the design minimum battery charging bus voltage (V₂) and a design minimum bus voltage (V₃) that is less than the design minimum battery charging bus voltage (V₂); and

(d) operating the Stirling engine at the maximum piston stroke and applying power from the battery to the bus for maintaining the bus voltage at the design minimum bus voltage (V₃) when the power supplied from the alternator operating at its maximum stroke is less than the power demand of the load.

2. An electrical power source having a free-piston Stirling engine including a piston driving a linear alternator and a battery for allowing the electrical power supplied from the power source to a load to, at times, exceed the maximum power that can be delivered from the free-piston Stirling engine driving the linear alternator, the power source further comprising:

(a) a Stirling engine controller, including a rectifier connected between the alternator and a bus to apply a voltage to the bus, the controller modulating the piston stroke between a maximum and a minimum stroke to maintain the bus voltage at a design nominal bus voltage (V₁) when and so long as the bus voltage does not fall below the design nominal bus voltage (V₁) and charging the battery if it is not charged, the controller also maintaining the maximum piston stroke when the bus voltage falls below the design nominal bus voltage (V₁);

(b) a bidirectional DC/DC converter connected between the battery and the bus, the DC/DC converter having a DC/DC converter control connected to and controlling the bidirectional DC/DC converter, the converter control including

(i) a voltage sensor having a sensing input connected to the bus to sense the voltage of the bus,

(ii) a battery charge state sensor having a sensing input connected to the battery to sense the charge state of the battery,

(iii) a control logic circuit connected to an output of the voltage sensor and to an output of battery charge state sensor, the control logic circuit

(1) initiating charging of the battery, if the battery is not charged, when the bus voltage is at the nominal bus voltage (V₁) or is in the range between the design nominal bus voltage (V₁) and a design minimum battery charging bus voltage (V₂) that is less than the design nominal bus voltage (V₁),

(2) disconnecting the battery so it can not charge when the bus voltage is in the range between the design minimum battery charging bus voltage (V₂) and a design minimum bus voltage (V₃) that is less than the design minimum battery charging bus voltage (V₂), and

(3) applying power from the battery through the bidirectional DC/DC converter to the bus to maintain the bus voltage at the design minimum bus voltage (V₃) when the power supplied from the alternator operating at its maximum stroke is less than the power demand of the load.

3. An electrical power source in accordance with claim 2 wherein the Stirling engine controller and a control circuit for the bidirectional DC/DC converter both use the same digital signal processor, microcontroller or other programmable microprocessor based controller.