Dual‐Mode Over‐Modulation Strategy for a Two‐Phase Hybrid Stepper Motor Fed by a Six‐Switch Inverter

ABSTRACT This paper addresses the limited voltage output capacity when a two‐phase six‐switch inverter is applied to a two‐phase hybrid stepper motor and the issue of still insufficient voltage output capacity after applying a traditional over‐modulation strategy based on the minimum phase error principle. It proposes a dual‐mode over‐modulation strategy by further subdividing the two regions of the conventional strategy and dynamically employing truncation or switching to fundamental voltage vectors based on phase angle. First, the expressions of the action time of adjacent basic vectors and the fundamental amplitude of output voltage are derived under both the traditional over‐modulation strategy and the dual‐mode over‐modulation strategy. Second, the relationship between the reference voltage modulation ratio and both the output voltage modulation ratio and harmonic distortion rate is analyzed. Finally, a platform is built for simulation and experimental verification. Simulation and experimental results show that the proposed dual‐mode over‐modulation strategy improves the maximum output voltage modulation ratio from 0.958 to 1.041 compared to the traditional over‐modulation strategy and improves the voltage utilization by 8.7%.