Abstract
This paper designs parameter adaptation algorithms for online
simultaneous identification of a two-parameter sigmoid inverter model
for compensating inverter nonlinearity to reduce the voltage error in
flux estimation for a position sensorless motor drive. The inverter
model has two parameters, a2 and a3, where a2 is “plateau voltage”,
and a3 is a shape parameter that mainly accounts for the stray capacitor
effect. Parameter a3 is identified by the (6k ± 1)-th order harmonics in
measured current. Parameter a2 is identified by the amplitude mismatch
of the estimated active flux. It is found that the classic linear flux
estimator, i.e., the hybrid of voltage model and current model, cannot
be used for a2 identification. This paper proposes to use a saturation
function based nonlinear flux estimator to build an effective indicator
for a2 error. The coupled identifiability of the two parameters is
revealed and analyzed, which was not seen in literature. The concept of
the low current region where the two-way coupling between a2 and a3
occurs is established. In theory, it is suggested to stop the inverter
identification in the low current region. However, the experimental
results in which dc bus voltage variation and load change are imposed,
have shown the effectiveness of the proposed online inverter
identification and compensation method, even in low current region.