Instant and seamless closing of control system of IPMSM after open-loop starting

Nowadays, position sensorless permanent magnet synchronous motor drives are gaining popularity quite rapidly and became almost a standard in many applications like compressors, high speed pumps, etc. All of those drives involve estimators to calculate speed and position of rotor, which are necessary for proper operation of vector control. At the same time, these estimators, except injection-based ones, work well in the middle and high speed range and cannot operate at low speeds. In order to overcome this problem, sensorless control systems include different starting techniques, where the most popular is open-loop starting. In this approach, the motor is accelerated in the open-loop mode until the speed, where estimator operates stably and then the control system is closed. However, the weakest point of this method is technology of closing the system, which typically creates transients and even can be a cause of losing stability. This paper proposes a method for instant and seamless transition from open-loop to closed loop, which perfectly works under different load conditions. The authors consider other starting techniques and compare them with a proposed method.