Power inverter circuit for adjusting symmetry of the AC-voltage without load-coupling

• US 9,071,168 B2
• Filed: 09/25/2006
• Issued: 06/30/2015
• Est. Priority Date: 09/25/2006
• Status: Active Grant

• Current Assignee: Voltwerk Electronics GmbH (Robert Bosch GmbH)
• Original Assignee: Voltwerk Electronics GmbH (Robert Bosch GmbH)
• Inventors: Knaup, Peter, Lenz, Thomas, Koch, Karl
• Primary Examiner(s): Berhane, Adolf
• Assistant Examiner(s): LEE III, HENRY E
• Application Number:
  US12/442,660
• Publication Number:
  US 20090316448A1
• Time in Patent Office: 3,200 Days
• Field of Search: 363 34- 35, 363 40- 41, 363 5601- 5612, 363/57, 363/71, 363/80, 363 95- 98, 363/109, 363 55- 5602, 363131-132, 363/65, 327/391, 327423-424, 327/433, 327/437
• US Class Current: 1/1
• CPC Class Codes: H02M 7/4803 with means for reducing DC component from AC output voltage
• CPC Class Codes: H02M 7/53803 with automatic control of output voltage or current

Abstract

The invention relates to a power inverter circuit for coupling a power station to a power supply system. The invention addresses the problem to reduce the risk of damages to components of the power station and the power supply system in the course of coupling action by providing a power inverter circuit for adjusting symmetry of the AC voltage before coupling the inverter output to a load, comprising: first switching means for selectively connecting a positive voltage to the inverter circuit output, second switching means for selectively connecting a negative voltage to the inverter output, and ohmic resistance means coupled in parallel to the inverter output, a controller for selectively switching the first and second switching means with a switching frequency to produce an AC voltage from the positive and negative voltage, wherein the controller is adapted to alter the duty ratio of the switching frequency to adjust the symmetry of the AC voltage produced by the inverter.

Claims

1. Power inverter circuit that produces an AC voltage at an inverter output and that adjusts a symmetry of the AC voltage before coupling the inverter output to a load, the symmetry being the amount of positive voltage in the AC voltage in relation to the amount of negative voltage in the AC voltage, the power inverter circuit comprising:

first switching means (50) for selectively connecting a positive AC voltage to the inverter output (61),

second switching means (51) for selectively connecting a negative AC voltage to the inverter output,

ohmic resistance means (80) coupled in parallel to the inverter output via third switching means (90), wherein that the ohmic resistance means functions as a substitute for the load of the power inverter during times when the power inverter output is disconnected from the load to allow the symmetry of the AC voltage output from the power inverter to be matched to the AC voltage of the load using the ohmic resistance means before coupling the power inverter output to the load,

fourth switching means (60,63) arranged between the ohmic resistance means and the inverter output for selectively coupling the inverter output to the load,

a controller for selectively switching the first and second switching means with a switching frequency and with respective amounts of on-time to produce an AC voltage from the positive and negative voltage,

wherein the controller is adapted to adjust the symmetry of the AC voltage produced by the inverter by altering the respective amounts of on-time of the first and second switching means.

2. Inverter circuit according to claim 1,

wherein the ratio of the on-time of the first switch means to the sum of the on-times of the first and second switch means is a duty ratio, and wherein the controller alters the duty ratio.

3. Inverter circuit according to claim 2,

characterized in that the controller is adapted to alter the duty ratio to synchronize the AC voltage produced by the inverter to an AC voltage provided in a load to which the inverter output is to be connected.

4. Inverter circuit according claim 1,

characterized in that the first and second switching means are adapted to be switched at frequencies of more than 1 kHz.

5. Inverter circuit according to claim 1, wherein the first and second switching means are switched at frequencies of more than 15 kHz.

6. Inverter circuit according to claim 1,

characterized by inductive-capacitive filtering means (70,71) coupled between inverting means and the inverter output.

7. Inverter circuit according to claim 6,

characterized in that the inductive-capacitive filtering means comprise capacitive resistance means (71) coupled in parallel to the ohmic resistance means.

8. Inverter circuit according to claim 6,

characterized in that the inductive-capacitive filtering means comprise inductive reactance means connected in series to the ohmic resistance means.

9. Inverter circuit according to claim 1,

further comprising a chopper controller coupled in parallel to the input of the inverter circuit.

10. A method of operating a power inverter circuit, the power inverter circuit producing an AC voltage at an inverter output, the method adjusting a symmetry of the AC voltage before coupling the inverter output to a load, the symmetry being the amount of positive voltage in the AC voltage in relation to the amount of negative voltage in the AC voltage, the method comprising:

coupling ohmic resistance means (80) in parallel with the inverter output (61, 62) as a substitute for the load of the power inverter during times when the power inverter output is disconnected from the load to allow the symmetry of the AC voltage to be matched to the AC voltage of the load using the ohmic resistance means before coupling the power inverter to the load,

selectively switching first switching means (50) for connecting a positive AC voltage to the inverter circuit output, the first switching means having a respective amount of on-time,

selectively switching second switching means (51) for connecting a negative AC voltage to the inverter output, the second switching means having a respective amount of on-time,

adjusting the symmetry of the output voltage by selectively altering the respective amounts of on-time of the first and second switching means, and

thereafter decoupling the ohmic resistance means from the inverter output.

11. Method according to claim 10, further comprising:

after adjusting the symmetric of the output voltage, coupling the inverter output to a load.

12. Method according to claim 10, further comprising, after adjusting the symmetric of the output voltage and before decoupling the ohmic resistance means from the inverter output, coupling the inverter output to a load.

13. Method according to claim 10,

characterized in that the inverted AC voltage is filtered using inductive-capacitive filtering means (70, 71) coupled between inverting means and the inverter output.

14. Method according to claim 10,

characterized in that the duty ratio of switching the first and second switching means (50, 51) is selectively altered for synchronizing the symmetry of the output voltage to a voltage in a public main system before coupling the inverter output to the load.