Patent ID: 7026772

Claim:
A position sensorless drive for PM synchronous motors, comprising: drive circuits operable for driving a PM synchronous motor; and a control module which receives voltage and current information from said PM synchronous motor, determines a rotor position of said PM motor, and generates control signals which control said drive circuits on the basis of said rotor position at zero, low and high motor speeds, wherein for relatively low speeds, said control module derives said rotor position on the basis of rotor inductance variations, and wherein said inductance variations are determined according to: V d r = R ⁢ ⁢ i d r + L ⁢ ⁢ ⅆ ⅆ t ⁢ i d r - L ⁢ ⁢ ω m ⁢ i q r ( 1 ) V q r = R ⁢ ⁢ i q r + L ⁢ ⁢ ⅆ ⅆ t ⁢ i q r - Δ ⁢ ⁢ L r ⁢ ⅆ ⅆ t ⁢ i q r + L ⁢ ⁢ ω m ⁢ i d r + λ r ⁢ ω m ( 2 ) Where: V d r and V q r are the direct and quadrature voltages, i d r and i q r are the direct and quadrature currents, ω m is the mechanical velocity of the rotor, λ r is the equivalent magnet flux, L is the average stator winding inductance, R is the stator resistance, ΔL r is the constant difference between the d-axis and q-axis inductances, due to saliency.