Electrical instrument, power management apparatus, power management system having same, and method for controlling same

A power management system includes a plurality of electrical instruments and a power management apparatus. Each of the plurality of electrical instruments has at least one characteristic function and an arbitration function which is discriminated from the characteristic function and requires power arbitration. Each electrical instrument includes a plurality of operation algorithms having at least one characteristic function, operation levels respectively corresponding to the plurality of operation algorithms, power information for the respective operation levels, and power information of the arbitration function. The power management apparatus receives power rate information from a power provider, determines the operation levels of the plurality of electrical instruments and controls the electrical instruments to be driven at the determined operation levels. When an arbitration function selection signal is received from at least one of the electrical instruments while the electrical instruments are driven, the power management apparatus adjusts operation levels of other electrical instruments.