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The control of four-quadrant converters (4QC) of traction vehicles fed by an ac railway grid has to meet very restrictive limitations with regard to harmonics and stability. The challenge is increased by continuously changing the position-dependent grid impedance and voltage harmonics already contained in the grid voltage. Testing a 4QC control in a lab, therefore, requires a railway grid representation that both emulates variable grid impedance and grid-voltage harmonics. The paper presents an innovative solution to this problem that employs a 4Q inverter with a suitably designed new control scheme. As the rated power is not high, compared to the traction vehicle fed, the control has to be effective, taking each switching event of the inverter into account. For the design of the control, a suitable simulation is needed, which is also presented in this paper. A comparison of simulation and measurement results is given, proving excellent results.