Nonlinear Effects of Three-Level Neutral-Point Clamped Inverter on Speed Sensorless Control of Induction Motor

In the model reference adaptive speed observer, the induction motor supply voltage is used as the input of the reference model. However, measuring the supply voltage complicates the system and increases the cost, so the command voltage calculated by the controller is generally used instead of the actual supply voltage in the drive system. However, due to the nonlinear effects of the inverter, the voltage calculated by the controller is different from the actual supply voltage, resulting in a speed observation deviation. This paper analyzes the multiple effects that cause the three-level neutral-point clamped (TL-NPC) inverter output voltage and command voltage deviation. A voltage deviation compensation measure based on the volt-second balance principle is proposed. In this context, the expression of the rotational speed deviation caused by the voltage deviation is derived rigorously and in detail. Finally, the effectiveness of the voltage compensation measure is verified by experiments. The experimental results are basically consistent with the theoretical derivation expressions. The method and analysis in this paper is applicable to induction motor speed sensorless control systems driven by two-level and other multilevel inverters.