Arc prevention in DC power systems
View Patent ↗A power system includes a DC power source having a maximum output voltage, a DC/AC inverter having an input coupled via a connection to the DC power source and an output for supplying AC power to a load, and a control circuit for controlling the DC/AC inverter. The control circuit is configured to maintain a DC voltage at the input of the DC/AC inverter above a threshold voltage to inhibit arcing as a result of a break in the connection between the DC power source and the DC/AC inverter. The threshold voltage is substantially equal to the maximum output voltage of the DC power source less a minimum arcing voltage for the connection between the DC power source and the DC/AC inverter.
1. A power system comprising:
a DC power source having a maximum output voltage;
a DC/AC inverter having an input coupled via a connection to the DC power source and an output for supplying AC power to a load; and
a control circuit for controlling the DC/AC inverter, the control circuit configured to maintain a DC voltage at the input of the DC/AC inverter above a threshold voltage by controlling an amount of current drawn by the DC/AC inverter from the DC power source to inhibit arcing as a result of a break in the connection between the DC power source and the DC/AC inverter;
wherein the threshold voltage is substantially equal to the maximum output voltage of the DC power source less a minimum arcing voltage for the connection between the DC power source and the DC/AC inverter.
2. The power system of claim 1 wherein the maximum output voltage of the DC power source is about 400 VDC and the threshold voltage is about 390 VDC.
3. The power system of claim 1 wherein the maximum output voltage of the DC power source is about 48 VDC and the threshold voltage is about 38 VDC.
4. The power system of claim 1 wherein the control circuit is configured to maintain the DC voltage at the input of the DC/AC inverter at a substantially constant voltage.
5. The power system of claim 1 wherein the control circuit is configured to allow the DC voltage at the input of the DC/AC inverter to vary within a range defined by the threshold voltage and the maximum output voltage of the DC power source.
6. The power system of claim 5 wherein the control circuit includes a maximum power point tracker (MPPT).
7. The power system of claim 1 wherein the DC power source includes at least one DC/DC converter having a maximum power point tracker (MPPT), and wherein the DC/DC converter is configured to run its MPPT when its output voltage is below the maximum output voltage.
8. The power system of claim 7 wherein the control circuit is configured to maintain the DC voltage at the input of the DC/AC inverter below the maximum output voltage of the DC power source.
9. The power system of claim 8 wherein the DC/AC inverter is a grid-tie inverter.
10. The power system of claim 8 wherein the DC power source includes a photovoltaic (PV) device.
11. The power system of claim 1 wherein the control circuit is configured to shut down the DC/AC inverter if the control circuit cannot maintain the DC voltage at the input of the DC/AC inverter above the threshold voltage.
12. A DC/AC inverter comprising:
an input for connection to a DC power source having a maximum output voltage;
an output for supplying AC power to a load; and
a control circuit configured to maintain a DC voltage at the input of the DC/AC inverter above a threshold voltage by controlling an amount of current drawn by the DC/AC inverter from the DC power source to inhibit arcing as a result of a break in said connection when the input of the DC/AC inverter is connected to the DC power source;
wherein the threshold voltage is substantially equal to the maximum output voltage of the DC power source less a minimum arcing voltage for said connection.
13. The DC/AC inverter of claim 12 wherein the control circuit is configured to maintain the DC voltage at the input of the DC/AC inverter at a substantially constant voltage.
14. The DC/AC inverter of claim 12 wherein the control circuit is configured to maintain the DC voltage at the input of the DC/AC inverter below the maximum output voltage of the DC power source.
15. The DC/AC inverter of claim 12 wherein the control circuit is configured to allow the DC voltage at the input of the DC/AC inverter to vary within a range between the threshold voltage and the maximum output voltage of the DC power source.
16. The DC/AC inverter of claim 15 wherein the control circuit includes an MPPT.
17. A method of operating a DC/AC inverter in a power system having a DC power source with a maximum output voltage coupled via a connection to the input of the DC/AC inverter, the method comprising:
controlling an amount of current drawn by the DC/AC inverter from the DC power source to maintain a DC voltage at the input of the DC/AC inverter above a threshold voltage to inhibit arcing as a result of a break in the connection between the DC power source and the DC/AC inverter;
wherein the threshold voltage is substantially equal to the maximum output voltage of the DC power source less a minimum arcing voltage of the connection between the DC power source and the DC/AC inverter.
18. The method of claim 17 wherein controlling includes controlling the amount of current drawn by the DC/AC inverter from the DC power source to maintain the DC voltage at the input of the DC/AC inverter at a substantially constant voltage.
19. The method of claim 17 wherein controlling includes allowing the DC voltage at the input of the DC/AC inverter to vary within a range between the threshold voltage and the maximum output voltage of the DC power source.
20. The method of claim 17 wherein controlling includes controlling the amount of current drawn by the DC/AC inverter from the DC power source to maintain the DC voltage at the input of the DC/AC inverter below the maximum output voltage of the DC power source.