Patent ID: 8653781

Claim:
A rotation speed searching apparatus for an induction motor, comprising: a first voltage/frequency controller for receiving a frequency command signal and converting the frequency command signal into a first control signal; a frequency searching module for generating a frequency scanning signal to scan a rotor frequency of the induction motor and processing the frequency scanning signal to generate a second control signal; a switch having one terminal connected to a voltage modulating module and the other terminal operatively connected to the first voltage/frequency controller or the frequency searching module for passing the first control signal or the second control signal to the voltage modulating module according to its operation; a DC-bus voltage error determining module connected to a control terminal of the switch for comparing a detected DC-bus voltage with a set DC-bus voltage; and a current error determining module connected to the control terminal of the switch for comparing a feedback current with a set current, wherein when the DC-bus voltage error determining module determines that the detected DC-bus voltage is larger than or equal to the set DC-bus voltage or when the current error determining module determines that the feedback current is smaller than or equal to the set current, the switch is switched to pass the first control signal to the voltage modulating module, such that the voltage modulating module controls an inverter to drive the induction motor according to the first control signal, and wherein when the DC-bus voltage error determining module determines that the detected DC-bus voltage is smaller than the set DC-bus voltage and when the current error determining module determines that the feedback current is larger than the set current, the switch is switched to pass the second control signal to the voltage modulating module, such that the voltage modulating module controls the inverter to drive the induction motor according to the second control signal, and then the DC-bus voltage error determining module compares the detected DC-bus voltage with the set DC-bus voltage and the current error determining module compares the feedback current with the set current iteratively.