Two improved flux weakening schemes for surface mounted permanent magnet synchronous machine drives employing space vector modulation

Surface-mounted synchronous permanent magnet (SMSPM) machines have been considered thus far unsuitable for an efficient, wide-range flux weakening operation. Two improved schemes proposed here provide stable and reliable operation up to a speed equal 3.5 times the base speed, without dependence on machine parameters, usage of look-up tables or DC bus voltage measurements. Both schemes employ space vector modulation with the option of smooth transition to six-step mode through the over-modulation range, maximizing the available torque. The first scheme ensures exact torque command tracking, while the second intrinsically gives a steady state error in the flux weakening area. The second method, on the other hand, is computationally simpler, and the steady state torque error is not a critical feature if the torque control loop is an inner loop.