Speed-Sensorless and Motor Parameters-Free Starting Method for Large-Capacity Synchronous Machines Based on Virtual Synchronous Generator Technology

The large-capacity electrically excited synchronous machines are widely applied in modern industrial production, and starting issues have become one of the most concerns of the synchronous motors in practical operation, such as the long starting time, large current shock, and poor adaption to a wide-ranging load. To deal with these starting problems, many starting methods have been proposed in previous studies. Regrettably, high-performance methods depend on specific motor parameters and complex sensorless technology, while simple and low-cost methods are low performance. In this article, a modified back-to-back starting method is proposed for large-capacity synchronous machines based on virtual synchronous generator (VSG) technology, where the cascaded H-bridge converter is controlled as a VSG to replace the prime mover and synchronous generator of the conventional back-to-back starting system. To reduce the current shock, an initial relative-angle regulator is designed. To improve the robustness in the presence of a wide-ranging load, a damping torque branch is adopted. Extra speed sensors are no longer required since the VSG speed is directly applied in the feedback control loop. To validate the effectiveness of the proposed approach, extensive simulation and experimental results are presented. Compared with conventional approaches, the proposed starting method achieves faster response, smaller starting current, and stronger robustness.