Modulation Restraint Analysis of Space Vector PWM for Dual Three-Phase Machines Under Vector Space Decomposition

For dual three-phase machines, vector space decomposition allows the control of fundamental and main harmonic components in
αβ
and
xy
subspaces, respectively. However, the modulation of voltage references in the two subspaces using the space vector pulsewidth modulation (SVPWM) is not independent but coupled. In that, voltage references of two subspaces cannot be modulated simultaneously beyond the modulation restraints, thereby distorting the voltage regulation and causing harmonics or even system misbehavior. Meanwhile, the fundamental voltage in
αβ
subspace responsible for electromagnetic torque generation should be prioritized and secured. Thus, this article proposes a systematic analysis of modulation restraints of three representative SVPWM techniques, i.e., the linear modulation range of
xy
subspace under an assured modulation index of the fundamental voltage. Voltage references of
xy
subspace within this range can be modulated successfully without affecting the assured modulation index and the margin left for harmonic control in
xy
subspace is then acknowledged. This can be used to limit the output of current controllers not to exceed the voltage modulation restraint, thereby avoiding the modulation failure. Finally, the experimental results validate the linear modulation range and demonstrate the modulation behaviors within and out of the linear modulation range.