A stator flux-oriented voltage source variable-speed drive based on DC link measurement

The authors present a new control strategy for variable speed drives, which is aimed at improving or even replacing existing volts per hertz (V/f) open loop variable-speed drives. This strategy uses only the DC link current and voltage, which are readily available in a V/f drive for protection purposes, to implement closed loop flux and torque control. Stator flux and electromagnetic torque feedback signals are derived from the DC link voltage, the DC link current, and inverter switching states. Digital implementation is seen to be possible with slight modification on existing V/f drives. Practical considerations in implementing such a system are emphasized, and experimental results are presented to show the feasibility of the scheme