An inverter is a device that controls the rotational speed of a motor. Controlling the rotational speed of the motor leads to energy saving and CO2 reduction. There are two types of inverter control, V / f control and vector control. V / f control is a control method that keeps the ratio between the voltage output from the inverter and the frequency constant. A single unit can rotate the motors of multiple devices, and is used for fans, air conditioners, etc. with small starting torque and load fluctuation. Vector control is a control method that performs vector calculation of the current direction of the motor, and enables highly accurate operation with few errors. Used in machine tools, cranes, extruders, etc., which have a large starting torque and load fluctuations. Some devices have wire saving and space saving, and some devices have a built-in braking circuit and do not require the selection of a braking unit.