1. Field of Invention
The invention relates to a motor controlling method and, in particular, to a controlling method of a motor state.
2. Related Art
As the applications of electronic devices become more popular, AC motor drives are used everywhere. FIG. 1 shows a schematic diagram of a DC bus voltage waveform versus the output frequency value when an AC motor drive is used to drive a motor for deceleration control. When the motor is decelerated, its regenerative power causes a rise in the DC bus voltage 10. Therefore, when the DC bus voltage 10 exceeds a over-voltage stall prevention level 11, the AC motor drive has to maintain the output frequency for a certain time 12a without any deceleration action until the DC bus voltage 10 is back to the safe range (i.e. lower than the over-voltage stall prevention level 11). This is to avoid an over-high DC bus voltage 10 that will result in over-voltage protection. A result of such continuous deceleration and speed maintenance is to elongate the motor deceleration time, which is the sum of multiple periods of maintenance time 12a and multiple periods of deceleration time 12b. Moreover, to remove the regenerative power generated when the motor is in a regeneration state, currently there are two solutions. One is to feed the regenerative power back to the power supply via a circuit for further use. However, this method often requires a higher circuit cost. Therefore, people usually adopt the other method, which is to install a braking unit of braking resistor in the device to consume the regenerative power. Although the cost of this method is lower than the previous one, it still requires extra charges for devices and maintenance.
Therefore, how to provide a controlling method that act according to the operation state of a motor is an important subject in the field.