Abstract: A static transfer switch is used for switching an output load from a first power source to a second power source. A first switching unit has a first pair of silicon controlled rectifiers (SCR). A second switching unit has a second pair of SCRs arranged in an anti-parallel configuration. The control circuit determines whether at least one of the SCRs is activated in accordance with the voltage between the gate and the cathode of the at least one SCR. If the voltage between the gate in the cathode is at least 150 mV, the control circuit indicates that the at least one of the SCR is activated.

Abstract: A method of controlling an uninterruptible power supply system to increase component life includes decreasing a maximum output power limit of the uninterruptible power supply system when a temperature that the uninterruptible power supply system is experiencing has increased and increasing the maximum output power limit when this temperature has decreased. In an aspect, this temperature is ambient temperature of an equipment enclosure of the uninterruptible power supply system in which at least a rectifier and inverter of the uninterruptible power supply system are located. In an aspect, the method further includes upon the system going into an overload condition, determining an overload time limit based upon the temperature, the overload condition and an initial load condition. In an aspect, the method further includes upon the system going into a back-up power mode, determining a battery autonomy based upon the temperature.

Abstract: An uninterruptible power supply system has a three-level T-Type inverter A method that improves clearing a short of a load coupled to an output of the inverter when the load experiences a short circuit event includes commutating with a controller each phase of the inverter in a two level mode current generation when output voltage and output current of that phase have the same direction and commutating each phase of the inverter in a three level mode current generation when the output voltage and output current of that phase have opposite directions.

Abstract: A UPS system may be operated selectively in either a high efficiency mode or a low efficiency mode. An inductor is connected in series between the transfer switch and a secondary power source. The transfer switch includes thyristors arranged in a reverse connected configuration. A controller synchronizes gate commands to the thyristors in order to synchronize reserve voltage introduced by the inverter. If the load currents are not in phase with a fundamental voltage of the secondary power source, the controller waits up to a first time period in order to estimate when current through the switches will reach zero. If the out of phase current will reach zero by the end of a second time period, the inverter is switched on at the end of the second time period.

Abstract: A UPS system may be operated selectively in either a high efficiency mode or a low efficiency mode. An inductor is connected in series between the transfer switch and a secondary power source. The transfer switch includes thyristors arranged in a reverse connected configuration. A controller synchronizes gate commands to the thyristors in order to synchronize reserve voltage introduced by the inverter. If the load currents are not in phase with a fundamental voltage of the secondary power source, the controller waits up to a first time period in order to estimate when current through the switches will reach zero. If the out of phase current will reach zero by the end of a second time period, the inverter is switched on at the end of the second time period.

Abstract: A static transfer switch is used for switching an output load from a first power source to a second power source. A first switching unit has a first pair of silicon controlled rectifiers (SCR). A second switching unit has a second pair of SCRs arranged in an anti-parallel configuration. The control circuit determines whether at least one of the SCRs is activated in accordance with the voltage between the gate and the cathode of the at least one SCR. If the voltage between the gate in the cathode is at least 150 mV, the control circuit indicates that the at least one of the SCR is activated.