A smart grid system includes a current sensor, and plural power conversion devices coupled to an AC grid. The current sensor measures a total current flowed through the AC grid, thereby providing a measured current value. The power conversion devices include a master power conversion device and plural slave power conversion devices. The master power conversion device receives the measured current value, thereby controlling an output power of the master power conversion device and providing a first duty cycle signal according to the measured current value. A first one of the slave power conversion devices which is coupled to the master power conversion device receive the first duty cycle signal, thereby controlling an output power of the first one of the slave power conversion devices according to the first duty cycle signal. The master power conversion device and the slave power conversion devices are communicated via a daisy chain connection.