A Methodology for High-Power Drives Emulation Using a Back-to-Back Configuration

Abstract

Validation of high-power converters at the development stage often cannot be performed using the real load. A testbench consisting of the Equipment Under Test (i.e., tested power converter) and an auxiliary power converter, preferably using power recirculation, can be used instead. A challenge for correct testing using this approach comes from the fact that the harmonic content of the currents can significantly differ between the testbench and the real system. This might strongly affect the loading of power switching devices compromising the reliability of the validation process. This paper proposes a methodology to select the operating conditions of both tested and auxiliary converters in the testbench to resemble a given operating condition of the actual system. Since identical behavior is not generally possible, a cost function will be used to trade-off among different factors (i.e., fundamental current magnitude and phase, harmonic content, etc.). The proposed approach evaluates a large number (hundreds of thousands) of testbench operating points in a few seconds and selects those which minimize the cost function. In a later stage, the selected points can be validated using detailed dynamic simulation. The selected conditions can then be used to test the converter in the testbench emulating the real system behavior in a given operating point condition. The proposed methodology was developed for railway electric drives but can be extended to other applications.INDEX TERMS Railway traction drive, machine emulation, back-to-back inverters, current harmonics, power recirculation, high-power converter testbench. I. NOMENCLATURE v a , v b , v c : phase voltages in the time domain. ⃗ v EU T : EUT complex vector voltage in the time domain. ⃗ v EU T f : fundamental component of EUT complex vector voltage in the time domain. ⃗ v EU T h : h th harmonic component of EUT complex vector voltage in the time domain (ω h = h ω f ). ⃗ V EU T : EUT voltage in the frequency domain. ⃗ V EU T f : fundamental component of EUT voltage in the frequency domain. ⃗ V EU T h : h th harmonic component of EUT voltage in the frequency domain. α EU T : angle of fundamental component of EUT complex vector voltage. φ: EUT power factor. Same cases apply for currents by replacing v/V and i/I. Same cases apply for AUX inverter by replacing EUT by AUX. Variables denoted by prime refers to testbench parameters.