Motor control system for centrifugal machine

A power control apparatus for controlling power supplied to a motor employed in a centrifugal machine comprising:

• an AC power supply providing the power to the motor;
• a smoothing capacitor:
• a voltage sensor detecting a voltage of said power supply to provide a voltage signal indicative thereof;
• a current sensor detecting a current of said power supply to provide a current signal indicative thereof;
• a charged voltage sensor detecting a charged voltage of said smoothing capacitor to provide a charged voltage signal indicative thereof;
• a bi-directional supply power-converting unit including rectifying elements connected to form a circular rectifying circuit and switching elements each connected to one of the rectifying elements in parallel, said bi-directional supply power-converting unit being connected at an ac terminal to said AC power supply and at a dc terminal to said smoothing capacitor for charging said smoothing capacitor;
• a bi-directional motor power-converting unit including rectifying elements connected to form a circular rectifying circuit and switching elements each connected to one of the rectifying elements in parallel, said bi-directional motor power-converting unit being connected at an ac terminal to the motor and at a dc terminal to said smoothing capacitor;
• a reactor disposed between the AC power supply and said bi-directional supply power-converting unit;
• and
• a control unit including an on-off switching circuit, said control unit controlling, in a motor power mode, the switching elements of said bi-directional motor power-converting unit with given operational timing to supply power to the motor and also controlling the on-off switching circuit to turn on and off the switching elements of said bi-directional supply power-converting unit with given on-off timing selected based on the voltage signal, the current signal, and the charged voltage signal provided by said voltage sensor, said current sensor, and said charged voltage sensor to have said bi-directional supply power-converting unit function as a step-up converter to charge said capacitor, in a motor braking mode wherein said bi-directional motor power-converting unit charges said smoothing capacitor with power of the motor regenerated during a braking operation, said control unit controlling the on-off switching circuit to turn on and off the switching elements of said bi-directional supply power-converting unit with given on-off timing selected based on the voltage signal, the current signal, and the charged voltage signal provided by said voltage sensor, said current sensor, and said charged voltage sensor to have said bi-directional supply power-converting unit function as a step-down converter to restrict the charged voltage of said capacitor from being increased above a preselected level for returning the power regenerated by the motor back to the AC power supply.