This study performs a design and parametric study of interior permanent-magnet (IPM) machines equipped with novel semi-overlapping windings (NSWs). The influence of the key design parameters including; number of turns per phase, stack length, distance and angle between V-shaped magnets, rotor yoke thickness, magnetic bridge width and thickness and number of magnet segments on the flux-weakening (FW) performance characteristics are evaluated in detail. The influence of material of segmentation (material of bridge namely, air or iron) is also considered. A combination of analytical calculation-based program and a time-stepping 2D finite-element analysis based program are employed to evaluate the FW characteristics. The accuracy of the FW calculations, particularly the performance at high-speed regions, is verified over changes in torque components; namely reluctance and permanent magnet (PM), inductance components, PM flux coefficient and inverse saliency ratio due to the change in considered design parameter. The electromagnetic torque, torque ripple, output power and FW capability are investigated by parametric analyses. Moreover, the power losses and efficiency maps together FW curves are calculated for the optimal NSW IPM machine. The experimental measurements, taken from manufactured prototype, verify that the performed analyses and methods described in this study are accurate and reliable.