To provide a controller which causes an AC motor which uses a solar cell as a power supply for rotation to rotate with maximum energy efficiency, without using a battery which is normally used for the stabilization of power.
A controller for an AC motor which uses a solar cell as a power supply for rotation supplies a DC power generated by the solar cell to the AC motor via an inverter 20, which is a DC/AC converting means. Furthermore, when an AC frequency control signal is supplied to the inverter 20 from the controller by using a relation that the load value of the AC motor as the load of the solar cell is changed by the change of the frequency of the driving power supply, the AC frequency control signal which makes the generated power of the solar cell maximum is supplied to make the AC motor always rotate with maximum efficiency.
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