Abstract: A server according to an embodiment includes a processor configured to receive a friend add request for a target account from a user terminal accessed with a user account; based on one of the user account and the target account being a protected account, transmit an approval request for the friend add request to a protector account connected to the protected account; and based on receiving a reply to the approval request from the protector terminal, add the target account to a friend list of the user account.

Abstract: A method for controlling an inverter in a system including a load, a motor for driving the load, and an inverter for operating the motor comprises when a load amount of the load is reduced to below a sleep level, checking whether a time corresponding to a sleep delay has lapsed; when the load amount of the load is still below the sleep level even after the sleep delay, varying an operating frequency of the motor, and if there is no change in a feedback from the load in response to the variation in the operating frequency, controlling the inverter to enter a sleep mode.

Abstract: Provided is a pump system. The pump system includes an AC (alternating current) electric motor, a converter, a smoothing unit, an inverter, a volt/hertz pulse width-modulation controller, and a main controller. The AC electric motor operates a pump which is a load. The converter receives AC power and converts the AC power into DC (direct current) power. The smoothing unit smoothes a DC voltage converted by the converter. The inverter converts the DC voltage output from the smoothing unit into an AC voltage. The volt/hertz pulse width-modulation controller applies switching voltage to a semiconductor switching device of the inverter. The main controller changes an operating frequency according to a load detected when the Ac electric motor is in operation and puts the AC electric motor to a sleep mode after determining a load operation status.

Abstract: The present disclosure discloses a multilevel inverter configured to output a 3-phase voltage to a motor by allowing a plurality of unit power cells forming one phase to be serially connected, the multilevel inverter, the multilevel inverter including a plurality of current sensors configured to detect an output current of the plurality of unit power cells.

Abstract: Provided is a pump system. The pump system includes an AC (alternating current) electric motor, a converter, a smoothing unit, an inverter, a volt/hertz pulse width-modulation controller, and a main controller. The AC electric motor operates a pump which is a load. The converter receives AC power and converts the AC power into DC (direct current) power. The smoothing unit smoothes a DC voltage converted by the converter. The inverter converts the DC voltage output from the smoothing unit into an AC voltage. The volt/hertz pulse width-modulation controller applies switching voltage to a semiconductor switching device of the inverter. The main controller changes an operating frequency according to a load detected when the Ac electric motor is in operation and puts the AC electric motor to a sleep mode after determining a load operation status.

Abstract: The present invention relates to a multilevel inverter comprising: a converter unit converting an inputted AC power source to a direct current (DC) power source; a film capacitor rectifying the DC power source converted by the converter unit; an inverter unit converting the rectified DC power source to a three-phase current in response to a pulse width modulation (PWM) control signal and outputting the current; a current detector detecting a current outputted from the inverter unit; a power cell main controller generating a voltage instruction and a voltage instruction using the detected current; and a PWM controller generating the pulse width modulation (PWM) control signal using the voltage instruction and frequency instruction.

Abstract: The present invention relates to a multilevel inverter comprising: a converter unit converting an inputted AC power source to a direct current (DC) power source; a film capacitor rectifying the DC power source converted by the converter unit; an inverter unit converting the rectified DC power source to a three-phase current in response to a pulse width modulation (PWM) control signal and outputting the current; a current detector detecting a current outputted from the inverter unit; a power cell main controller generating a voltage instruction and a voltage instruction using the detected current; and a PWM controller generating the pulse width modulation (PWM) control signal using the voltage instruction and frequency instruction.

Abstract: An apparatus and method for controlling an inverter are disclosed to allow an inverter to provide a stable output voltage to a motor regardless of a change in a DC input voltage. A difference value between a reference voltage according to a predetermined rated voltage of a motor and a DC voltage of the inverter is obtained, a ratio of an output command frequency to a predetermined reference frequency is applied to the difference value to obtain a compensation output voltage value, a final compensation output voltage value is obtained by compensating the detected DC input voltage value with the compensation output voltage, and an output voltage of the final compensation output voltage value to the motor by the inverter. Thus, the stable output voltage of the inverter can be provided to the motor regardless of the change in the input voltage.

Abstract: An apparatus and method for controlling an inverter are disclosed to allow an inverter to provide a stable output voltage to a motor regardless of a change in a DC input voltage. A difference value between a reference voltage according to a predetermined rated voltage of a motor and a DC voltage of the inverter is obtained, a ratio of an output command frequency to a predetermined reference frequency is applied to the difference value to obtain a compensation output voltage value, a final compensation output voltage value is obtained by compensating the detected DC input voltage value with the compensation output voltage, and an output voltage of the final compensation output voltage value to the motor by the inverter. Thus, the stable output voltage of the inverter can be provided to the motor regardless of the change in the input voltage.