Overmodulation Strategy for Inverters with a Single DC-Link Current Sensor

The single current sensing method is widely used in home appliances due to the merits of low-cost and small size. However, it requires minimum on-duty to detect the phase currents separately in each pulse width modulation (PWM) period, and as a result, dead regions take place around the vertices of the space vector hexagon. These dead regions also affect the overmodulation. In this paper, an overmodulation method is proposed for single current shunt inverters (SCSIs). It has a property of keeping linear modulation index (MI) up to the maximum. Fourier series expansion is utilized in the process of derivation, and resulting in 12-step operation at the maximum. In addition, the technique guarantees the seamless transition among different operation modes depending on the magnitude of the reference voltage. The proposed method is demonstrated by experimental results.