A method for emulating a reactive source impedance for a generator connected to a load. The method comprises adjusting an output of the generator, wherein, in response to adjustment of the output, a first measured value M1 calculated with respect to a weighted sum of voltage v, current i and derivatives of the voltage v and the current i tends to a first setpoint S1 for M1. The method also includes receiving a second setpoint S2 for a second measured value M2 and adjusting S1 to adjust the second measured value M2 of a conventional measure of generator output towards the second setpoint S2 for M2, wherein holding M1 constant emulates a desired source impedance of the generator.