Extension of Low-Speed Self-Sensing Capability for Induction Machines by Using an FPGA

Self-sensing control (SSC) of induction machines (IMs) down to zero stator frequency is still a challenge. In this context, a simple observer structure for rotor speed estimation is analysed with respect to its lower speed limit. Using methods enabled by oversampling with an FPGA, the extent to which the lower speed limit can be reduced is investigated. First, the non-linearity of the inverter is improved by using deadtime compensation (DTCO), which pre-calculates the currents at the switching instants and mitigates the interference voltage. Second, a grey box model (GM) filter is used to increase the signal-to-noise ratio of the current measurement. The GM filter is derived by using the difference between machine models with and without iron resistance. Finally, the two approaches are combined.