Uninterruptible power supplies with converter operation conditioned upon static switch commutation and methods of operation thereof
A UPS is operated by deasserting a static switch drive signal, e.g., a gate signal to a thyristor, and then delaying provision of power from a converter circuit of the UPS, e.g., an inverter or other source of AC power, until after the switch has current commutated to an off state. For example, expiration of a predetermined time interval following deassertion of the switch drive signal may be detected, and the converter circuit may be enabled to drive the output of the UPS responsive to the detected expiration of the predetermined time interval. Alternatively, a current in the static switch may be detected, and the converter circuit may be enabled to drive the output of the UPS responsive to the detected current. The invention may be embodied as methods and apparatus.
1. A method of operating a UPS, the method comprising:
asserting a switch drive signal at a switch to couple an AC source at an AC input of the UPS to an AC output of the UPS through the switch;
deasserting the switch drive signal; and then
inhibiting control of the AC output of the UPS by a converter circuit of the UPS coupled to the AC output of the UPS until after the switch has current commutated to an off state.
2. A method according to claim 1 , comprising current commutating the switch to the off state responsive to discharge of a capacitance at the AC output of the UPS.
3. A method according to claim 1 , wherein inhibiting control of the AC output of the UPS by a converter circuit of the UPS coupled to the AC output of the UPS until after the switch has current commutated to an off state comprises:
detecting expiration of a predetermined time interval following deassertion of the switch drive signal; and
enabling the converter circuit to drive the AC output of the UPS responsive to the detected expiration of the predetermined time interval.
4. A method according to claim 1 , wherein inhibiting control of the AC output of the UPS by a converter circuit of the UPS coupled to the AC output of the UPS until after the switch has current commutated to an off state comprises:
detecting a current in the switch; and
enabling the converter circuit to drive the AC output of the UPS responsive to the detected current.
5. A method according to claim 1 , wherein the switch comprises a thyristor.
6. A method according to claim 1 , wherein inhibiting control of the AC output of the UPS by a converter circuit of the UPS coupled to the AC output of the UPS until after the switch has current commutated to an off state comprises delaying provision of power from an inverter circuit of the UPS.
7. A method according to claim 1 , wherein inhibiting control of the AC output of the UPS by a converter circuit of the UPS coupled to the AC output of the UPS until after the switch has current commutated to an off state comprises maintaining an output of the converter circuit coupled to the AC output in a high-impedance state until after the switch has current commutated to the off state.
8. An uninterruptible power supply (UPS), comprising:
an AC input;
an AC output;
a converter circuit operative to generate an AC voltage at the AC output;
a switch operative to couple an AC source at the AC input to the AC output through the switch in an on state responsive to assertion of a switch drive signal and to decouple the AC input from the AC output in an off state responsive to a current in the switch following deassertion of the switch drive signal; and
a control circuit operative to control the converter circuit such that control of the AC output by the converter circuit is inhibited until the switch current commutates to the off state.
9. A UPS according to claim 8 , wherein the control circuit is operative to detect expiration of a predetermined time interval following deassertion of the switch drive signal and to enable the converter circuit to drive the AC output of the UPS responsive to the detected expiration of the predetermined time interval.
10. A UPS according to claim 8 , wherein the control circuit is operative to detect a current in the switch and to enable the converter circuit to drive the AC output of the UPS responsive to the detected current.
11. A UPS according to claim 8 , wherein the switch comprises a thyristor.
12. A UPS according to claim 8 , wherein the converter circuit comprises an inverter circuit.
13. A UPS according to claim 8 , wherein the control circuit is operative to maintain an output of the converter circuit coupled to the AC output in a high-impedance state until the switch current commutates to the off state.
14. An uninterruptible power supply (UPS), comprising:
an AC input;
an AC output;
an inverter circuit coupled to AC output and operative to generate an AC voltage at the AC output; and
a thyristor coupled between the AC input and the AC output; and
a control circuit operative to inhibit control of the AC output by the inverter circuit until the thyristor commutates to an off state following deassertion of a gate signal at the thyristor.
15. A UPS according to claim 14 , wherein the control circuit is operative to detect expiration of a predetermined time interval following deassertion of the gate signal and to enable the inverter circuit responsive to the detected expiration of the predetermined time interval.
16. A UPS according to claim 14 , wherein the control circuit is operative to detect a current in the thyristor and to enable the inverter circuit responsive to the detected current.
17. A UPS according to claim 14 , wherein the thyristor comprises a pair of anti-parallel connected silicon-controlled rectifiers (SCRs).
18. A UPS according to claim 14 , wherein the control circuit is operative to maintain an output of the inverter circuit coupled to the AC output in a high-impedance state until the thyristor commutates to the off state following deassertion of the gate signal at the thyristor.