A Ground Fault Detection Method for Double Fed Induction Machines via DC Grounding Resistor Voltage Evaluation

The use of Double Fed Induction Machines (DFIM) is widely implemented in wind farms and pumping stations due to their capacity to regulate voltage and frequency. Typically, they are connected to low-power converters to vary the machine's operational point by changing the frequency of the rotor, which is, in fact, one of the most expensive components. Nevertheless, the injection of pulsed voltages into the rotor can cause high insulation stresses, leading to the deterioration of these machines. A fault in the insulation can provoke a ground fault, potentially damaging the machine. In this context, this paper proposes a new method for detecting ground faults in power-converter fed DFIMs. The method involves placing a grounding resistor at the midpoint of the DC bus, where the voltage is then measured. The frequency response of this measurement allows detecting ground faults, not only in the DFIM's rotor, but also in its stator or even in the converter's own DC bus. To validate this method, numerous simulations were conducted in MATLAB-Simulink, complemented by experimental tests on a 7 kW Double Fed Induction Generators (DFIG) test bench. These tests yielded positive results.