A lot of researches about speed sensor-less vector control methods of the IM have been published and applied to practical systems. However, because of various errors caused by dead time, temperature variation of resistance and so on, the speed estimation error is inevitable in the practical applications. The inverter voltage control error is very sensitive to phase current near zero cross. Therefore, the speed estimation becomes unstable when the phase current zero cross and the zero frequency condition occur simultaneously. In order to solve these problems, this paper proposes a novel method to reduce the inverter voltage control error. The phase current references are forbidden to stay near zero, where the voltage control error is very sensitive to the phase current. The phase current non-zero control causes the harmonics which influences the speed estimation. The harmonics is compensated appropriately by a novel method, which cancels the harmonic component in the input signals to the speed estimator. The experimental results with phase current non-zero control showed good performance in low speed range.
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