Master device that changes data communication speed in accordance with the number of slave devices

A master device capable of connecting to slave devices, which correspond to a first number not less than two of motors, via a serial communication bus for carrying out data transmission and reception at a first communication speed, in order to control a system in which a first number not less than two of motors in the same number as the number of inverters can be connected in parallel to a DC link part, which is connected to an alternating-current power source via a converter, via each the first number of the inverters, the number of the slave devices being a second number, the master device comprising:

• a call unit configured to transmit a call signal to verify the presence or absence of the slave devices, which correspond to the motors, to all the slave devices, which correspond to all the motors connected to the DC link part, after the master device is activated;
• a response reception unit configured to receive a response signal to the call signal from each of all the slave devices, which correspond to all the motors connected to the DC link part, and to determine a third number which is the number of all the slave devices, which correspond to all the motors connected to the DC link part, based on the number of received response signals;
• and
• a communication speed change determination unit configured to determine whether or not a data communication speed of data transmitted and received between the master device and the third number of slave devices should be changed from the first communication speed to a second communication speed different from the first communication speed during a period from the time when the third number is determined to the time when the drive of the motors is stopped, in accordance with a result of comparison of between the third number and a fourth number less than the second number and equal to or more than one.