An Active Modulation Technique for Single-Phase Grid-Connected CSI

Due to the interaction between the rectified voltage appearing on the dc side of the grid-connected current source inverter (CSI) and the dc inductor, the input current on the dc side inherently consists of the second-order harmonic of the grid frequency. This harmonic component will be modulated by the pulsewidth modulation (PWM) signal that results in generating low-order harmonics at the output and thus injecting into the grid. This paper presents an active nonlinear modulation technique for reducing the low-order harmonics. The method requires simple analog circuitry to modify the modulation function of the sinusoidal PWM (SPWM) scheme. It is based on measuring the dc and ac components of the dc inductor current to compensate the modulation effect from the dc side to the ac side of the CSI. Apart from reducing the harmonic content, this method can also reduce the required value of the dc inductor. Modeling, design, and analysis of the method are given. The proposed method has been tested with a 1 kW, 220 V, 50 Hz prototype, powered by a dc voltage of 80 V. The results are favorably compared with the performance of the CSI with the SPWM scheme.