Generally the permanent magnet synchronous motor can use energy efficiently as compared with an induction motor. A permanent magnet synchronous motor has less generation of heat than an induction motor. Therefore, the permanent magnet synchronous motor can save weight compared to an induction motor. Therefore, the demand for a permanent magnet synchronous motor is increasing in recent years.
The permanent magnet synchronous motor needs to give and control voltage from a VVVF inverter according to the position of the rotor of each permanent magnet synchronous motor. Therefore, the inverter needs to perform individual control for every permanent magnet synchronous motor. The VVVF inverter of one set each of exclusive use of a permanent magnet synchronous motor has been located. The gate control device was set in each VVVF inverter, in order to control each VVVF inverter.
For this reason, in the system configuration which controls the conventional permanent magnet synchronous motor individually, the number of apparatus increased and enlargement of the whole device and the increase in cost had become a problem.