Sensorless stand alone variable speed system for distributed generation

The following paper presents a variable speed stand alone power generating system. The system consists of a double fed induction machine and power electronic converter connected to the rotor. A topology and a control system allow for stand alone operation. An external power source was used for preliminary excitation. After that, the system can operate autonomously and take excitation power from the stator. The control system is based on stator voltage space vector referred to rotating frame. The speed of the rotating frame responds to stator frequency. The system is controlled by rotor current which amplitude is adjusted by controller of the stator voltage component related to x axes, whereas the rotor current frequency is controlled by stator voltage component related to y axes. In this way the stator output voltage frequency is speed independent and the control system operates without any mechanical sensor. For design a simulation program PSIM with DLL files is applied. The results of controllers calculation in a wide speed range are presented. A laboratory system was built and tested. As a controller a DSP SHARC^™ system with support ALTERA^™/ FPGA is used. The results of the laboratory tests present the generating system in transients when a step load is applied.