DC-side leakage current reduction for single phase full-bridge power converter/inverter

• US 9,048,756 B2
• Filed: 03/08/2012
• Issued: 06/02/2015
• Est. Priority Date: 03/07/2012
• Status: Active Grant

• Current Assignee: Virginia Tech Intellectual Properties, Inc.
• Original Assignee: Virginia Tech Intellectual Properties, Inc.
• Inventors: Dong, Dong, Luo, Fang, Boroyevich, Dushan, Mattavelli, Paolo
• Primary Examiner(s): Dole, Timothy J
• Assistant Examiner(s): Ahmad, Shahzeb K
• Application Number:
  US13/415,141
• Publication Number:
  US 20130235628A1
• Time in Patent Office: 1,181 Days
• Field of Search: 323/207, 363/44, 363/47, 363/46, 363/71, 363/131, 363/127, 363/132
• US Class Current: 1/1
• CPC Class Codes: H02M 1/123 Suppression of common mode voltage or current
• CPC Class Codes: H02M 7/797 using semiconductor devices only
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers
• CPC Class Codes: Y10T 29/49117 Conductor or circuit manufacturing

Abstract

Leakage current through stray or parasitic capacitance (which is particularly large in devices such as photovoltaic cell arrays and which are damaged by such leakage currents) due to common mode switching noise in a full bridge single phase power converter is reduced at high frequencies by magnetically coupling the two phase legs on the AC side of the power converter and connecting mid points of the AC and DC sides of the power converter and is reduced at low frequencies by use of a feedback arrangement that modifies sinusoidal modulation of the switches of the full bridge converter to function as an active filter. The magnetic coupling for the two phase legs is designed in a simple manner to avoid saturation based on volt-second considerations.

Claims

1. A full-bridge single phase bidirectional AC/DC power converter having two phase legs on an AC side thereof and a capacitor connected between said two phase legs, said converter including

a plurality of switches connected in a full bridge configuration,

a choke comprising magnetically coupled windings connected in series in respective ones of said two phase legs,

a split capacitor connected between said two phase legs and in parallel with said capacitor connected between said two phase legs, and

a connection between a mid-point of said split capacitor and a mid-point of a split capacitor connected between DC voltage rails on a DC side of said power converter,

wherein said switches in said full bridge configuration are driven by a pulse width modulated signal that is modified from sinusoidal modulation to provide active filtering of common mode voltage variation on said two phase legs by said full bridge configuration.

2. The power converter as recited in claim 1, wherein said connection includes a damping resistor.

3. The power converter as recited in claim 1, wherein said DC side of said power converter is connected to a photovoltaic cell.

4. The power converter as recited in claim 3, wherein said AC side of said power converter is connected to an AC power distribution grid.

5. The power converter as recited in claim 1, wherein said AC side of said power converter is connected to an AC power distribution grid.

6. The power converter as recited in claim 1, further comprising

a source of a sinusoidal waveform modulation signal,

a circuit responsive to common mode voltage variation on said two phase legs to modify said sinusoidal waveform modulation signal to provide a modified sinusoidal waveform modulation signal,

a source of a triangular waveform modulation signal, said triangular waveform modulation signal having a frequency higher than a frequency of said sinusoidal modulation signal, and

a comparator to compare amplitudes of said modified sinusoidal waveform modulation signal and said triangular waveform modulation signal, wherein said comparator controls said plurality of switches connected in said full bridges configuration.

7. The power converter as recited in claim 6, further including

an L-C-L filter in said AC side of said power converter.

8. The power converter as recited in claim 6, wherein said connection includes a damping resistor.

9. The power converter as recited in claim 6, wherein said DC side of said power converter is connected to a photovoltaic cell.

10. The power converter as recited in claim 9, wherein said AC side of said power converter is connected to an AC power distribution grid.

11. The power converter as recited in claim 6, wherein said AC side of said power converter is connected to an AC power distribution grid.

12. The power converter as recited in claim 1, further comprising

a feedback path to combine at least two signals, each corresponding to a voltage on said DC side of said converter due to said common mode voltage variation in said two phase legs, to provide said modification of said sinusoidal modulation signal.

13. The power converter as recited in claim 1, further comprising

a feedback path including an adder to combine two signals corresponding to a voltage on said DC side of said converter due to said common mode voltage variation on said two phase legs in accordance with different transfer functions to provide a combined signal and a further adder to provide said modification of said sinusoidal modulation signal.

14. A method of reducing common mode noise and leakage current through parasitic capacitance in a single phase, full bridge power converter having unipolar modulation of switches and having two phase legs on an AC side of said power converter and a capacitor connected between said two phase legs, said method comprising steps of

magnetically coupling said two phase legs opposingly,

connecting a split capacitor across said two phase legs in parallel with said capacitor connected between said two phase legs to form a mid-point on said AC side of said converter,

connecting a split capacitor across a DC side of said power converter to form a mid-point on said DC side of said power converter, and

connecting said mid-point of said split capacitor on said AC side of said power converter to said mid-point of said split capacitor on said DC side of said power converter

wherein said switches in said full bridge configuration are driven by a pulse width modulated signal that is modified from sinusoidal modulation to provide active filtering of common mode voltage variation on said two phase legs by said full bridge configuration.

15. The method as recited in claim 14 further comprising a step of

modifying said unipolar modulation from a sinusoidal pulse width modulation in accordance with low frequency common mode noise appearing on said DC side of said power converter.

16. The method as recited in claim 15, wherein said modifying step is performed using a feedback arrangement operating as an active filter.

17. The method as recited in claim 14, including the further step of

designing a device for performing said magnetic coupling to avoid saturation at maximum volt-second points of said unipolar modulation.