Method for adaptively adjusting PWM duty cycle, circuit and motor driving system

A circuit for adaptively adjusting a PWM duty cycle, for a motor driving system, comprising:

• a sampling module, configured to receive a direct current bus voltage and sample the direct current bus voltage, so as to obtain sample signals of the direct current bus voltage;
• a digital filtering module, connected to an output end of the sampling module, and configured to perform a low-pass filtering on the sample signals to obtain low-pass filtered signals;
• an under-voltage determination module, connected to an output end of the digital filtering module, and configured to determine whether the direct current bus voltage is under-voltage based on the low-pass filtered signals;
• a duty cycle calculation module, connected to the output end of the sampling module and an output end of the under-voltage determination module, and configured to calculate a new duty cycle D′ and a new amplitude corresponding to the new duty cycle D′ when the direct current bus voltage is not under-voltage;
• wherein the new duty cycle D′ satisfies:
• D′=D*A/B;
• wherein D denotes a duty cycle obtained from a control loop of the motor driving system, A denotes a previous sample signal of the direct current bus voltage, and B denotes a current sample signal of the direct current bus voltage;
• a duty cycle determination module, connected to an output end of the duty cycle calculation module, and configured to determine whether the new duty cycle D′ is greater than 100%;
• and
• an adjustment module, connected to the output end of the duty cycle calculation module and an output end of the duty cycle determination module, and configured to initiate a weak magnetic control when the new duty cycle D′ is greater than 100%, and apply the new amplitude to a sine wave generator when the new duty cycle D′ is less than or equal to 100%, so as to adjust a duty cycle of PWM signals through the new amplitude.