Abstract
Flux-weakening (F-W) based on feedback voltage regulation is commonly adopted in interior permanent magnet synchronous motor drives. Voltage space vector magnitude is controlled in a closed loop, modifying the current reference, following a value related to the inverter limitations. A stable and fast voltage control allows to operate with lower voltage margin, leading to higher torque versus speed capability. Theoretical analysis and gain adaptation of the F-W regulation loop was reported by Bolognani et al. partially overcoming the difficulties due to the strong nonlinearity of the plant. An approximated closed-form design method was proposed and refined by Bedetti et al. This allowed the application of the algorithm to drives where autotuning is needed, ensuring stability and dynamical performances. A fundamental enhancement is introduced in this article, namely the use of a speed regulator with explicit torque reference output. An advantage of this technique is that the speed loop becomes linear in the whole operating range and an accurate control of machine torque is possible. Thanks to a novel gain adaptation for the voltage regulator, the F-W behavior is decoupled from the speed control response at speed steady-state (at constant or slowly changing torque), improving performance of the overall drive control. Adoption of this novel method allows smooth operation with invariant dynamical behavior of both the speed and F-W control loops. Extensive simulations and experimental tests are reported to prove the validity of the proposal. A sensorless operation of the drive system has also been considered in the tests to further validate the proposed solution.