The demand for robust and energy-efficient traction inverters in heavy-duty electric vehicles (HDVs) has accelerated the development of advanced Power-Hardware-in-the-Loop (PHIL) testbeds that enable realistic and repeatable validation scenarios. This paper proposes an improved back-to-back (B2B) hardware test setup that replicates the full power map of a traction inverter under realistic drive cycle conditions. A passive-damped LCL filter is introduced between inverter phases to enhance power control and maintain a high power factor over a wide frequency range, particularly in the motor's field-weakening region. A two-stage optimization framework is developed to determine the filter parameters, ensuring minimal inductor values while achieving constant power transfer. Furthermore, the feasibility of active damping using capacitor voltage and current sensing is investigated to reduce external power supply losses in the passive damping resistances. The proposed configuration enhances testbed accuracy and efficiency, facilitating safer tests and more effective high-power inverter validation.