| 摘要 |
PROBLEM TO BE SOLVED: To carry out a stable invert or control by inputting the output of a frequency set circuit for setting the primary frequency of an electric motor in a function generation circuit having a specific hysteresis characteristic and controlling the ratio between the voltage of the electric motor and frequency to nearly constant in V/F ratio constant control circuit by the output signal. SOLUTION: When a compressed air requested by a load is near the rating of an air compressor 1, an electric motor 2 is set so as to be driven by a rated frequency, namely a rated number of rotation by a frequency set circuit 5 and the air compressor 1 is operated by this set number of rotation. When a requested compressed air is a half or less of the capacity of the air compressor 1, the electric motor 2 is set so as to be driven by a half of a rated frequency by the frequency set circuit 5, but a stop signal is outputted at about a half of the rated frequency in the function generation circuit 4 having a hysteresis characteristic. When the compressed air requested by the load is short, the set of the frequency set circuit 5 is raised and the operation is carried out by the frequency of a half or more of the rated frequency. |
