POWER CONDITIONING UNIT

• US 20100214808A1
• Filed: 01/12/2007
• Published: 08/26/2010
• Est. Priority Date: 01/13/2006
• Status: Active Grant

• Current Assignee: Tesla Inc.
• Original Assignee: Enecsys Limited
• Inventors: Rodriguez, Cuauhtemoc
• Granted Patent: US 8,089,785 B2
• Time in Patent Office: Days
• US Class Current: 363/37
• CPC Class Codes: H02M 5/458 using semiconductor devices only
• CPC Class Codes: H02M 7/4807 having a high frequency intermediate AC stage
• CPC Class Codes: H02M 7/53871 with automatic control of output voltage or current
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers
• CPC Class Codes: Y02E 10/76 Power conversion electric or electronic aspects
• CPC Class Codes: Y10S 323/906 Solar cell systems

Abstract

The present invention relates to a power conditioning unit for delivering power from a dc power source to an ac output, particularly ac voltages greater than 50 volts, either for connecting directly to a grid utility supply, or for powering mains devices independent from the mains utility supply. We describe a power conditioning unit for delivering power from a dc power source to an ac mains output, the power conditioning unit comprising an input for receiving power from said dc power source, an output for delivering ac power, an energy storage capacitor, a dc-to-dc converter having an input connection coupled to said input and an output connection coupled to the energy storage capacitor, and a dc-to-ac converter having an input connection coupled to said energy storage capacitor and an output connection coupled to said output, wherein said energy storage capacitor has a capacitance of less than twenty microfarads.

Claims

1-28. -28. (canceled)

29. A power conditioning unit for delivering power from a dc power source to an ac mains power supply output, the power conditioning unit comprising:

an input for receiving power from said dc power source;

an output for delivering ac power;

an energy storage capacitor;

a dc-to-dc converter having an input connection coupled to said input and an output connection coupled to the energy storage capacitor; and

a dc-to-ac converter having an input connection coupled to said energy storage capacitor and an output connection coupled to said output;

wherein said energy storage capacitor has a capacitance of less than twenty microfarads.

30. A power conditioning unit according to claim 29, wherein said dc-to-dc converter comprises:

at least one power device for transferring power from the input connection of the dc-to-dc converter to the output connection of the dc-to-dc converter;

a sensing circuit for sensing a voltage on said input connection; and

a driver circuit for driving said at least one power device responsive to said sensing to control said power transfer;

wherein the dc-to-dc converter further comprises a reference voltage generator, and wherein the driver circuit is configured to substantially minimise a difference between the reference voltage and the sensed voltage.

31. A power conditioning unit according to claim 29, wherein said dc-to-ac converter comprises:

at least one power device for transferring power from the input connection of the dc-to-ac converter to the output connection of the dc-to-ac converter;

a low-pass filter coupled to said input connection;

a sensing circuit for sensing an output from the low-pass filter and comparing with a reference; and

a driver circuit for driving said at least one power device responsive to said sensing to control said power transfer.

32. A power conditioning unit according to claim 31, wherein the driver circuit is configured to substantially minimise a difference between the output from the low-pass filter and the reference.

33. A power conditioning unit according to claim 31, wherein the sensing circuit is configured to sense an output voltage from said low-pass filter and compare with a reference voltage.

34. A power conditioning unit according to claim 31, wherein the sensing circuit is configured to periodically compare said output from the low-pass filter with said reference in synchronisation with the ac output.

35. A power conditioning unit according to claim 29, wherein said energy storage capacitor comprises a non-electrolytic or film-type capacitor.

36. A power conditioning unit according to claim 29, further comprising a controller that controls the transfer of power from the dc power source into the ac mains while maintaining the voltage and power of the dc power source constant, and that allows a sinusoidal fluctuation on the average voltage across the energy storage capacitor, said sinusoidal fluctuation corresponding to a sinusoidal current injection into the ac mains.

37. A power conditioning unit comprising a dc-to-dc converter for delivering power from a dc power source to a dc output, the converter being configured to maintain a voltage on the dc power source substantially constant over a range of dc output voltages, the converter comprising:

an input for receiving power from said dc power source;

an output for delivering dc power;

at least one power device for transferring power from the input to the output;

a sensing circuit for sensing a voltage on said input;

a driver circuit for driving said at least one power device responsive to said sensing to control said power transfer; and

a controller that controls the transfer of power from the dc power source into said dc output while maintaining the voltage and power of the dc power source constant.

38. A power conditioning unit for delivering power from a dc power source to an ac output, the inverter being configured to maintain a substantially sinusoidal output voltage or current over a range of dc power source voltages, the power conditioning unit comprising:

an input for receiving power from said dc power source;

an output for delivering ac power;

at least one power device for transferring power from the input to the output;

a low-pass filter coupled to said input;

a sensing circuit for sensing an output from the low-pass filter and comparing with a reference; and

a driver circuit for driving said at least one power device responsive to said sensing to control said power transfer.

39. A power conditioning unit as claimed in claim 38, wherein a link capacitor of the power conditioning unit connected in parallel between an output of a dc-to-dc converter of said power conditioning unit and an input of a dc-to-ac converter of said power conditioning unit is not an electrolytic capacitor;

and wherein the power conditioning unit has no electrolytic capacitors.

40. A power conditioning unit as claimed in claim 38 for providing said ac power to an ac electricity supply, the power conditioning unit comprising:

a power conversion stage for voltage conditioning of the dc power source;

a power conversion stage for power injection into the electricity supply;

a dc capacitor for energy buffering from the dc power source to the electricity supply; and

two control blocks, one of which controls the power conversion stage for voltage conditioning from a dc power source to the dc capacitor for energy buffering, and another that controls the power conversion stage for power injection into the electricity supply.

44. A power conditioning unit as claimed in claim 40, where the control block for the power conversion stage for power injection into the electricity supply maintains the average voltage of the capacitor constant by using proportional and derivative (PD) control and by adjusting the amplitude of the current injection.

45. A power conditioning unit as claimed in claim 44, where the control block for the power conversion stage for power injection into the electricity supply controls the sinusoidal shape of the current injection into the electricity supply.

46. A power conditioning unit as claimed in claim 45, where the control block for the power conversion stage for power injection into the electricity supply includes a sensor for measuring the voltage across the dc capacitor and conditions the resulting signal by using said Low Pass Filter (LPF).

47. A power conditioning unit as claimed in claim 46, where the control block for the power conversion stage for power injection into the electricity supply compares a reference voltage to the signal available from said Low Pass Filter and generates an error that is sampled at periodic intervals using a Sample and Hold (SH) circuit.

48. A power conditioning unit as claimed in claim 47, where the control block for the power conversion stage for power injection into the electricity supply generates a current amplitude reference in response to the error obtained using a proportional and derivative (PD) compensator.

41. A power conditioning unit as claimed in 40, where the control block for the power conversion stage for voltage conditioning maintains the voltage at the terminals of the dc power source constant, hence maintaining a constant flow of power from the dc power source into the dc capacitor.

42. A power conditioning unit as claimed in claim 41 where the control block for the power conversion stage for voltage conditioning utilises pulse width modulation (PWM) to control the amount of power transferred from the dc power source into the dc capacitor.

43. A power conditioning unit as claimed in claim 42 comprising a voltage sensor at the terminals of the dc power source used to acquire its actual voltage, the reading of which is further compared to a reference voltage in order to generate a proportional error that drives the PWM control.