Power control system and method for motor preheating

A power control system for motor preheating, comprising:

• a motor receiving a three-phase voltage to operate;
• a current sensor electrically connected to the motor, wherein the current sensor senses a motor current outputted by the motor during an operation of the motor;
• a power calculation module electrically connected to the current sensor, wherein the power calculation module calculates an output power of the motor during operation according to a voltage command and the motor current;
• a power error calculation module electrically connected to the power calculation module, wherein the power error calculation module receives the output power and a power command and calculates a power error according to the power command and the output power;
• a power control module electrically connected to the power error calculation module, wherein the power control module receives the power error and outputs a current braking command according to the power error, wherein the current braking command is between an upper limit value and a lower limit value, if the power error received by the power control module within a first period of time continues to be positive, a first slope of a variation of the current braking command output by the power control module during the first period of time corresponds to a positive value, if the power error received by the power control module within a second period of time continues to be negative, a second slope of the variation of the current braking command output by the power control module during the second period of time corresponds to a negative value, if the power error received by the power control module within a third period of time continues to be zero, the output current braking command of the power control module during the third period of time is not adjusted;
• a current control module electrically connected to the power control module, the power calculation module and the current sensor, wherein the current control module receives the current braking command from the power control module and receives the motor current from the current sensor, and the current control module calculates the voltage command according to the current braking command and the motor current;
• and
• a voltage control module electrically connected to the current control module and the motor, wherein the voltage control module receives the voltage command from the current control module and outputs the three-phase voltage according to the voltage command, and the motor is operated in a stationary state and a stator of the motor is preheated.