Direct torque and flux control (DTFC)has been widely used for interior permanent magnet synchronous machine (IPMSM)drives due to its excellent torque and flux response. To ensure wide speed range electrical drives, field-weakening (FW)algorithms are generally used. However, most of the existing FW methods for DTFC based drives have constrained constant power speed range (CPSR)due to the limited usage of DC-link voltage. This is undesirable for applications, such as electrified transportation. Moreover, many of these FW approaches are heavily dependent on machine parameters. This can lead to degraded performance of drives or even control instability under some circumstances. To extend the CPSR and simultaneously enhance the parameter robustness of FW operation, this paper proposes a new robust FW algorithm for DTFC based IPMSM drives. The proposed algorithm achieves extended CPSR and reduced parameter dependency. Its effectiveness is verified through simulations.