Adaptive regulation system for a linear alternator driven by a free-piston stirling engine

• US 4,642,547 A
• Filed: 08/19/1985
• Issued: 02/10/1987
• Est. Priority Date: 08/19/1985
• Status: Expired due to Fees

• Current Assignee: Sunpower Corporation (Totalenergies Se)
• Original Assignee: Sunpower Corporation (Totalenergies Se)
• Inventors: Redlich, Robert W.
• Primary Examiner(s): Hickey, R. J.
• Application Number:
  US06/766,491
• Time in Patent Office: 540 Days
• Field of Search: 322/3, 322/7, 322/8, 322/93, 310/15, 290/1 R
• US Class Current: 322/3
• CPC Class Codes: F02G 1/0435 the engine being of the free piston type
• CPC Class Codes: F02G 1/045 Controlling
• CPC Class Codes: G05D 19/02 characterised by the use of electric means
• CPC Class Codes: H02K 7/1884 structurally associated with free piston engines
• CPC Class Codes: H02P 9/04 Control effected upon non-electric prime mover and dependent upon electric output value of the generator

Abstract

A load regulator for a linear alternator driven by a free piston Stirling engine. A substantially constant output voltage is maintained across the useful load by shunting a portion of the armature output current of the alternator through a variable energy absorbing conductance and varying that conductance in proportion to changes in the output voltage of the alternator in order to maintain a constant total armature power output. The regulator may be made more efficient by forming the armature coil as a plurality of series connected coils by one or more taps and then switching the number of series coil turns in connection to the load approximately in inverse proportion to the square root of the steady state power demand of the load so that the total armature output power is switched between discrete levels while the output voltage is maintained constant for all those levels by the variable impedance.

Claims

1. An adaptive load regulator for a linear alternator driven by a free piston Stirling engine, having a heat energy source, the alternator having an armature circuit and a useful load connected to the armature circuit, and further including a stepped armature system for controlling the stroke amplitude of the Stirling engine, the regulator and the stepped armature system comprising:

(a) a controllably variable conductance shunted across the armature;

(b) a negative feedback control circuit comprising;

(i) a summing circuit;

(ii) a voltage detector means connected to the armature circuit for detecting a signal which is proportional to the alternator output voltage and connected to apply the detected signal to an input of the summing circuit;

(iii) a reference signal source connected to apply its reference signal to another input of the summing circuit; and

(iv) an amplifier having its input connected to the output of the summing circuit and its output connected to the control input of the controllable, variable conductance for applying a signal which is proportional to the difference of the input signals at the summing circuit to a control input of the variable conductance for varying the conductance in proportion to detected voltage changes;

(c) an armature coil divided into a plurality of coils serially connected by one or more taps;

(d) circuit means having an input connected to the useful load for detecting the steady state output power demand of the useful load; and

(e) logic switching means having a control input connected to the output of the power demand detecting means and having its switches connected to the taps of the armature and to the useful load for connecting a selected one of said taps as the armature output to the useful load to provide an effective total number of armature coil turns in inverse proportion to the square root of a selected, discrete total armature power output above the detected steady state power demand of the useful load;

whereby the stroke is changed to discrete stroke amplitudes in approximate inverse proportion to the square root of the useful load power demand.

2. A regulator in accordance with claim 1 wherein the voltage detector is a peak detector.

3. A regulator in accordance with claim 2 wherein said amplifier is a high gain amplifier.

4. An improved regulator in accordance with claim 1 wherein the steady state output power demand detector comprises means for detecting the instantaneous real part of the useful load impedance.

8. A regulator in accordance with claims 1 or 5 and further comprising a thermal feedback control system connected to detect the heat source temperature applied to the free piston Stirling engine and adjust energy input to maintain a selected reference temperature.

5. A stepped armature regulator for a linear alternator driven by a free piston Stirling engine, the alternator having an armature circuit and a useful load connected to the armature circuit, the regulator comprising:

(a) an armature coil divided into a plurality of coils serially connected by one or more taps;

(b) circuit means having an input connected to the useful load for detecting the steady state output power demand of the useful load;

(c) logic switching means having a control input connected to the output of the power demand detecting means and having its switches connected to the taps of the armature and to the useful load for connecting a selected one of said taps as the armature output to the useful load to provide an effective total number of armature coil turns in inverse proportion to the square root of a selected, discrete total armature power output above the detected steady state power demand of the useful load, whereby the stroke is changed to discrete stroke amplitudes in approximate inverse proportion to the square root of the useful load power demand;

(d) a controllably variable energy absorbing load having a control input and connected to absorb energy from the Stirling engine; and

(e) a feedback control having an input connected to detect a signal proportional to the engine stroke amplitude and an output connected to the control input of the energy absorbing load to vary the energy absorption of the controllable load in inverse proportion to detected stroke amplitude changes from a selected reference stroke amplitude.

6. A regulator in accordance with claim 5 wherein the detected signal which is proportional to stroke amplitude is the armature voltage.

7. An improved regulator in accordance with claim 6 wherein the steady state output power demand detector comprises means for detecting the instantaneous real part of the useful load impedance.

9. A method for controlling the stroke amplitude of a linear alternator connected to a free piston Stirling engine having an armature coil connected to a load, the method comprising:

(a) forming the armature coil as a plurality of series connected coils by one or more taps;

(b) switching a number of the series coil turns in connection to the load approximately in inverse proportion to the square root of the steady state power demand of the useful load.

10. A method in accordance with claim 9 further comprising:

(a) shunting a portion of the armature output current of the alternator through a variable impedance; and

(b) varying said impedance in proportion to changes in the output voltage of the alternator from a selected output voltage.

11. A method in accordance with claims 9 or 10 further comprising the step of maintaining the input temperature applied to the free piston Stirling engine substantially at a selected temperature.