Overmodulation Strategy for Voltage Source Inverter With a Single DC-Link Current Sensor

With a single shunt resistor, it is possible to sense the phase currents, although some dead regions exist around vertices of the voltage hexagon. In this article, an overmodulation method is presented for such single current shunt inverters. Regions near vertices of voltage hexagon are defined as holding regions, and the rest are defined as linear regions. The overmodulation strategy is developed based on the Fourier analysis: The magnitude of reference voltage determines the arc radius in the linear region and the holding angle of the holding region. By adjusting either the arc radius or the holding angle, the desired modulation index (MI) can be output. It is particularly useful for low-cost inverters, since it is implemented with an additional look-up table for induction motor or permanent magnet synchronous motor control. The linearity is maintained between the reference MI and its output MI until it reaches to the maximum, 12-step operation. In addition, the technique provides the seamless transition from space vector modulation to 12-step operation. The effectiveness is evidenced by the experimental results.