Maximum power tracking solar power system

• US 6,281,485 B1
• Filed: 09/27/2000
• Issued: 08/28/2001
• Est. Priority Date: 09/27/2000
• Status: Expired due to Fees

• Current Assignee: Aerospace Corporation
• Original Assignee: Aerospace Corporation
• Inventors: Siri, Kasemsan
• Primary Examiner(s): Riley, Shawn
• Application Number:
  US09/670,776
• Time in Patent Office: 335 Days
• Field of Search: 250/203.4, 126/573, 126/574, 126/600, 126/601, 323/272, 323/906, 320/150
• US Class Current: 250/203.4
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: H02J 7/35 with light sensitive cells
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers
• CPC Class Codes: Y10S 323/906 Solar cell systems

Abstract

A maximum power tracker maximizes the power deliverable from a power source, such as a solar array using increasing, decreasing and maintaining states controlled by a set point signal modulated by a dither signal for stabilized regular power tracking during under demand conditions and maximum power tracking during periods with over demand conditions of a load. Multiple converters and respectively maximum power trackers can be coupled in parallel using shared bus control signal for fault tolerant equalized power conversion through the converters.

Claims

1. A system for providing power from a source providing source power at a source current at a source voltage to a load receiving load power at a load current at a load voltage, the load having variable amounts of load demand for the load power, the source providing variable amounts of the source power, the system comprising,

a converter coupled between the source and the load, the converter for converting the source power into the load power, and

a maximum power tracker connected to the converter and the source for controlling the source power and the load power, the maximum power tracker sensing the load current and source voltage and controlling the converter for maximizing the source power to a peak power point at a respective peak power source voltage when the load demand exceeds the source power, the maximum power tracker increasing the source voltage for increasing the source power toward the peak power point when the source power is below the peak power point and the source voltage is below the peak power source voltage and when the load demand exceeds the source power, the maximum power tracker decreasing the source voltage for increasing the source power toward the peak power point when the source power is below the peak power point and when and the source voltage is above the peak power source voltage and when the load demand exceeds the source power, the maximum power tracker maintaining the source voltage constant at the peak power source voltage when the source power is at peak power point and when the load demand exceeds the source power, the maximum power tracker generating a control signal for controlling the converter to control the source voltage for operating the source at the peak power point when the load demand exceeds the source power, the maximum power tracker controlling the converter for peak power tracking when increasing or decreasing or maintaining the source voltage when the load demand exceeds the source power, the maximum power tracker regulating the load voltage at a regulated load voltage when the available powers from the source exceeds the load demand.

2. The system of claim 1 further comprising,

an input bus stabilizer coupled to the source voltage for stabilizing under the closed loop control a control loop extending through the converter and maximum power tracker along the source voltage and the control signal,

an output bus stabilizer coupled to the load for stabilizing a regulation control loop extending through the load voltage and the converter, and

output current sensor for sensing the load current and providing the maximum power tracker with the load current signal.

3. The system of claim 1 further comprising,

an external battery for storing external battery power having a battery current and battery voltage,

a thermister providing a temperature signal, the external battery coupled to the load for providing power to the load when the load voltage is less than the external battery voltage

a battery converter for providing battery current and battery voltage to an external battery and

a battery controller for controlling the battery converter through a battery control signal for charging the external battery at the battery voltage and battery current dependent on the temperature of the battery.

4. The system of claim 1 further comprising,

a load battery for storing power at a load battery voltage, the load battery coupled to the load for providing power to the load when the load voltage is less than load battery voltage, and

a load battery charger for charging the load battery when the load voltage is regulated.

5. The system of claim 1 wherein the source is a solar power source.

6. The system of claim 1 wherein,

the maximum power tracker serves to maximize the amount of source power converted into the load power when the load demands exceeds the source power.

7. The system of claim 1 wherein the converter is a plurality of converters coupled between the source and the load, each of the converters is coupled to the control signal serving as a bus signal to each of the converters to control the converters to provide equal current sharing contributions to the load current.

8. The system of claim 1 wherein the converter comprises,

a power stage having a converter input signal for controlling the respective load current and load voltage to the load, and

an error amplifier for sensing the load voltage and generating an error signal for regulating the load voltage to a regulation voltage when the source powers exceeds the load demand, the error signal driving the converter input signal during load voltage regulation, and

a coupling means for coupling together the control signal and the converter input signal and the error signal, the converter input signal being the control signal when the control signal is lesser than the error signal during the peak power tracking when the load demand exceeds the source powers, converter input signal being the error signal when the control signal is greater than the error signal during load voltage regulation when the source powers exceeds the load demand.

9. The system of claim 8 wherein the regulation voltage is a reference voltage divided by a scalar.

10. The system of claim 8 wherein the maximum power tracker generates the control signal from the source voltage and a set point signal, the set point signal increasing when the source power is increasing and the source voltage is increasing, the set point signal decreasing when the source power is increasing and the source voltage is decreasing, the set point signal maintaining when the source is operating at the peak power point at the peak power source voltage, the set point signal and source voltage combined into the control signal driving the converter connected to the source voltage for controlling the source voltage to the set point signal under closed loop control.

11. The system of claim 10 wherein,

the set point signal is dithered by a dither signal having a dither frequency for dithering the set point signal about a tracking signal, the set point signal serving to dither the source voltage and load current about the dither frequency,

the maximum power tracker senses the source voltage and the load current at repetitive present and previous times for continuously providing and updating present and previous source voltage signals and for continuously providing and updating present and previous load current signals as present and previous source power signals, the present and previous source voltage signals defining a changed source voltage, the present and previous source power signals providing a changed source power, and

the set point signal is increasing or decreasing or maintaining respectively when the tracking signal is increasing or decreasing or maintaining, the tracking signal increasing when the changed source power signal is increasing and when the changed source voltage signal increasing, the tracking signal decreasing when the changed source power signal is increasing and the changed source voltage signal are decreasing, the tracking signal maintaining when the changed source power signal is less than a predetermined minimum value.

12. The system of claim 11, wherein the maximum power tracker comprises,

a first filter for filtering the source voltage having the dither frequency into a filtered source voltage signal,

a first sample and hold circuit for sampling the filtered source voltage signal into the present and previous source voltage signals,

a second filter for filtering the load current having the dither frequency into a filtered power signal, and

a second sample and hold circuit for sampling the filtered power signal into the present and previous power signals.

13. The system of claim 11 further comprising,

an input bus stabilizer coupled to the source voltage for stabilizing under the closed loop control a control loop extending through the converter and maximum power tracker along the source voltage and the control signal and the power stage and the converter input signal,

an output bus stabilizer coupled to the load for stabilizing a regulation control loop extending through the load voltage and power stage and error amplifier and coupling means, and

output current sensor for sensing the load current and providing the maximum power tracker with the load current signal, and

an output capacitor for filtering ripples of the load voltage signal.