Abstract: A method is disclosed which makes use of an intelligent transfer algorithm for a UPS when the UPS is required to switch from a high efficiency mode of operation (VFD or VI) to an independent mode of operation (VFI), as a result of an under voltage condition occurring on the bypass line of the UPS. The method involves performing successive voltage measurements at a plurality of points during a first half cycle of an AC mains (Vout) signal to integrate the Vout signal until a zero crossing of the Vout signal is detected. Successive voltage measurements are used to detect the disruption of the Vout signal and a percentage of missing voltage area from the Vout signal during the disruption. The UPS then supplies a compensation voltage (Vcomp) which is added to the Vout signal to restore the Vout signal to a level at least approximately equal to a nominal AC mains voltage output signal (Voutnominal).

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 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: 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 method is disclosed which makes use of an intelligent transfer algorithm for a UPS when the UPS is required to switch from a high efficiency mode of operation (VFD or VI) to an independent mode of operation (VFI), as a result of an under voltage condition occurring on the bypass line of the UPS. The method involves performing successive voltage measurements at a plurality of points during a first half cycle of an AC mains (Vout) signal to integrate the Vout signal until a zero crossing of the Vout signal is detected. Successive voltage measurements are used to detect the disruption of the Vout signal and a percentage of missing voltage area from the Vout signal during the disruption. The UPS then supplies a compensation voltage (Vcomp) which is added to the Vout signal to restore the Vout signal to a level at least approximately equal to a nominal AC mains voltage output signal (Voutnominal).

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.