Instant Closing of Permanent Magnet Synchronous Motor Control Systems at Open-Loop Start

Abstract

Nowadays, position sensorless permanent magnet synchronous motor drives are gaining popularity quite rapidly, and have become almost standard in many applications such as compressors, high speed pumps, etc. All of these drives involve estimators to calculate the speed and the position of the rotor, which are necessary for proper operation of vector control. While these estimators, with the exception of injection-based ones, work well in the middle and high-speed ranges, they cannot operate at low speeds. In order to overcome this problem, sensorless control systems include different starting techniques, with the most popular being open-loop starting. In this approach, the motor is accelerated in open-loop mode until it reaches the speed where estimator operates stably, then the control system is closed. However, the weakest point of this method is the technology of closing the system, which typically creates transients and can even be the cause of loss of stability. This paper proposes a method for instant and seamless transition from open-loop to closed loop which works perfectly under different load conditions. Other starting techniques are considered and compared with the proposed method.

Comparison of Feedback Field-Weakening Techniques for Synchronous Machines with Permanent Magnets

“…The motor starts in an open-loop mode with the following seamless closing, as discussed in [56]. After which, the inverter executes speed commands, which are processed by the S-shaped speed limiter in order to provide smooth accelerations and decelerations.…”

“…This minimum speed is enough for the compressor to operate and does not need further improvements, considering that sensorless operation at low speeds is a challenging task [54]. The motor starts in an open-loop mode with the following seamless closing, as discussed in [56]. After which, the inverter executes speed commands, which are processed by the S-shaped speed limiter in order to provide smooth accelerations and decelerations.…”

Performance Comparison of Traction Synchronous Motors with Ferrite Magnets for a Subway Train: Reluctance versus Homopolar Variants

“…(1) In this application, the average loss of the FaSHM is 100%(7.4 − 7.16)/7.4 = 3.4% less than that of FaSynRM; (2) By adjusting the excitation flux, the maximum armature current for the FaSHM is 833/539 = 1.54 times less than for the FaSynRM, which potentially makes it possible to significantly reduce the cost of power modules of the traction inverter; (3) The active volume of magnetic cores, excluding the stator housing, in the FaSynRM is 100%(47.1 − 45.4)/47.1 = 3.9% higher than in the FaSHM; (4) The length of the FaSHM stator laminations is less than that of FaSynRM by 100%(240 − 227)/240 = 5.4%; the length of the FaSHM, taking into account the gap for installing the excitation winding, is greater by 100%(260 − 240)/260 = 7.7%; (5) The mass of active materials of the FaSHM is greater than that of the FaSynRM by 100%(359.2 − 98.9 − 241)/(359.2 − 98.9) = 7.4% excluding the housing and sleeve; (6) The cost of the FaSHM active materials is 100%(1152.7 − 818.2)/818.2 = 29.0% higher than that of the FaSynRM (excluding the housing and sleeve) due to the greater mass of copper and magnets; (7) The maximum modulus of the demagnetizing force in the case of the FaSHM is greater than in the case of the FaSynRM by (2.5 − 2) = 0.5 kOe. In this case, the demagnetization margin for the FaSynRM is (4 − 2) = 2 kOe, and for the FaSHM is (4 − 2.5) = 1.5 kOe, where 4 kOe is the coercive force of ferrite magnets.…”