4 December 2019
permanent magnet machines, PI control, torque, brushless DC motors, machine vector control, voltage control, electric potential, control system synthesis, magnetic flux, numerical analysis, demagnetisation, machine theory, flux-weakening space vector control algorithms, permanent magnet brushless DC machines, torque equations, demagnetising current components, PMBDCM torque demand, DC link, PMBDCM constraint management, torque ripple, synchronous reference frames, PI regulator, SVC design, PMBDCM voltage equation, trapezoidal shapes, back-emf, constant-power speed range, numerical simulation
The design of space vector control (SVC) systems suitable for flux-weakening operation of permanent magnet brushless DC machines (PMBDCMs) is presented in this study. The proposed design approach enables overcoming the critical issues arising from the non-linearities of PMBDCM voltage and torque equations; these issues derive from the trapezoidal shapes of back-emfs and affect PMBDCM constraint management significantly. The SVCs presented in this study have been developed within two different synchronous reference frames, both of which enable distinguishing torque and demagnetising current components clearly. Therefore, reference torque current component is determined in accordance with PMBDCM torque demand, while reference demagnetising current component is computed through a voltage follower PI regulator, which processes the voltage deficit detected on the DC-link. In this regard, a novel synchronous reference frame is proposed in this study, which improves PMBDCM constraint management and results into a wider constant-power speed range, but at the cost of some torque ripple. The enhanced performances achievable by SVC approaches are highlighted by numerical simulations, which regard the comparison among the SVCs and an SVC with no flux-weakening capability, at different operating conditions.