Patent ID: 8143838

Claim:
A phase current estimation apparatus for a motor comprising: an inverter that sequentially commutes electrical conductions of a three-phase AC motor according to a pulse width modulated signal; a pulse width modulated signal generation unit that generates the pulse width modulated signal according to a carrier wave signal; a DC side current sensor that detects a DC side current of the inverter; a phase current estimation unit that estimates a phase current based on the DC side current detected by the DC side current sensor; a determination unit that determines whether or not a magnitude of a command voltage vector of the motor is less than a predetermined lower limit voltage; a vector decomposition unit that decomposes the command voltage vector into two vector components which have same magnitudes as the predetermined lower limit voltage for every two adjacent periods in units of a period of a carrier wave and same predetermined phase value at phase-angle-leading-side and phase-angle-lagging-side from the command voltage vector, in a case where the magnitude of the command voltage vector is less than the predetermined lower limit voltage as a determination result of the determination unit; a phase determination unit that determines whether or not a phase of each of the vector components has a value within a predetermined phase range including a phase of a reference voltage vector; and a vector component changing unit that changes the phase and the magnitude of the vector component so that the phase of the vector component is allowed to have a value outside the predetermined phase range and so that a product of a cosine value of a phase difference with respect to the command voltage vector of the vector component and the magnitude of the vector component is allowed to be same as the magnitude of the command voltage vector, in the case where the phase of the vector component has a value within the predetermined phase range as a determination result of the phase determination unit.