The present disclosure is directed to a method for controlling a system that includes a modular set having a plurality of variable frequency modular units. The method includes setting a load ratio range for the plurality of variable frequency modular units, inputting an energy adjustment amount, and setting different operations for the modular set based on the energy adjustment amount. During a first operation, a first frequency adjustment amount of a corresponding variable frequency modular unit is determined based on the energy adjustment amount and an operating position of the corresponding variable frequency modular unit. During a second operation, a second frequency adjustment amount of a corresponding variable frequency modular unit is determined based on the energy adjustment amount and the operating position of the variable frequency modular unit. The first operation or the second operation causes the variable frequency modular units to operate within the load ratio range.