Harmonic reduce system and uninterruptible power supply including same

An inverter connected between a direct current bus and a load, wherein the inverter is a three-phase inverter, the invertor comprising:

• a harmonic reduce control system for controlling the inverter, the harmonic reduce control system comprising:
• a phase-locked loop controller, a voltage sum loop controller, a repetitive controller, a current loop controller, and a harmonic obtaining module, wherein the harmonic obtaining module detects a harmonic value of a load current from a load side;
• when a power grid and the load are directly connected in a bypass mode, the load current is equal to a sum of an inverter output current and a power grid current;
• wherein the harmonic reduce control system is configured to generate an inverter current reference value based on a first current value output by the voltage sum loop controller and the harmonic value, the phase-locked loop controller calculates a real-time frequency value based on a voltage of the power grid, the repetitive controller obtains, through calculation, a repetitive controller output value based on the inverter current reference value, the inverter output current used as a negative feedback, and the real-time frequency value output by the phase-locked loop controller, and the current loop controller outputs a first duty cycle based on the repetitive controller output value;
• and
• wherein the harmonic reduce control system controls a transistor of the inverter based on the first duty cycle to limit the inverter output current, so that harmonics of the power grid current in the bypass mode are reduced.

An uninterruptible power supply comprising:

• a three-phase inverter connected between a direct current bus and a load;
• and
• a harmonic reduce control system configured to control the three-phase inverter, wherein the harmonic reduce control system comprises:
• a phase-locked loop controller, a voltage sum loop controller, a repetitive controller, a current loop controller, and a harmonic obtaining module, wherein the harmonic obtaining module detects a harmonic value of a load current from a load side;
• when a power grid and the load are directly connected in a bypass mode, the load current is equal to a sum of an inverter output current and a power grid current;
• wherein the harmonic reduce control system is configured to generate an inverter current reference value based on a first current value output by the voltage sum loop controller and the harmonic value, the phase-locked loop controller calculates a real-time frequency value based on a voltage of the power grid, the repetitive controller obtains, through calculation, a repetitive controller output value based on the inverter current reference value, the inverter output current used as a negative feedback, and the real-time frequency value output by the phase-locked loop controller, and the current loop controller outputs a first duty cycle based on the repetitive controller output value,
• wherein the harmonic reduce control system controls a transistor of the inverter based on the first duty cycle to limit the inverter output current, so that harmonics of the power grid current in the bypass mode are reduced, and
• wherein the uninterruptible power supply directly supplies power from the power grid to the load in the bypass mode.