Method for compensating instantaneous power failure in medium voltage inverter and medium voltage inverter system using the same

A method for compensating instantaneous power failure in an inverter including a plurality of power cells, the method comprising:

• determining whether an input voltage of the plurality of power cells is less than or equal to a first threshold voltage;
• decreasing, when the input voltage is less than or equal to the first threshold voltage, an output frequency of the inverter;
• determining whether a voltage of a direct current (DC) link is greater than or equal to a second threshold voltage;
• and
• increasing, when the voltage of the DC link is greater than or equal to the second threshold voltage, the output frequency of the inverter,
• wherein the increasing of the output frequency of the inverter comprises monitoring change of the voltage of the DC link resulting from regenerative energy supplied from a load to the plurality of power cells and a restored input voltage and increasing the output frequency by an increment of the voltage of the DC link at a time when the input voltage of the plurality of power cells greater than or equal to the first threshold voltage is restored,
• the method further comprising:
• maintaining, when the increment of the voltage of the DC link resulting from the regenerative energy is eliminated, the output frequency of the inverter for a predetermined time,
• wherein the maintaining is performed after the monitoring of the change and the increasing of the output frequency of the inverter.