Analytical design and auto-tuning of adaptive flux-weakening voltage regulation loop in IPMSM drives with accurate torque regulation

Flux-Weakening (F-W) based on feedback voltage regulation is commonly adopted in Interior Permanent Magnet Synchronous Motor (IPMSM) drive systems. Voltage vector magnitude is controlled in closed-loop by modifying the current reference space vector, following a reference value related to the inverter limitations. Stable and fast voltage control allows to operate with lower voltage margin, which leads to higher torque vs. speed capability. Theoretical analysis and gain adaptation of the flux-weakening regulation loop was reported in [1][2], partially overcoming the difficulties due to the strong non-linearity of the plant. An approximated closed-form design method was proposed in [3]. This allows application of the algorithm to drives where auto-tuning is needed, ensuring stability and dynamical performances. An important enhancement is introduced in this paper, namely the use of torque reference-based speed regulator. An advantage of this technique is that the speed loop becomes linear in the whole operating range. Thanks to a novel gain adaptation for the voltage regulator, the flux-weakening behavior is decoupled from the speed control response at speed steady-state (at constant or slowly-changing torque), improving stability and accuracy of the overall drive control. Thanks to the novel proposal, smooth operation is obtained, with invariant dynamical behavior of both the speed and F-W loops. Simulations and experimental tests are reported to prove the validity of the proposal, also comprising sensorless operation.