Photovoltaic grid-connected inverter with current tracking control

Inverter which is essential in the photovoltaic grid-connected generation system faces an important problem that is how to adjust PWM (pulse width modulation) control signals to output current keeping sinusoidal and in phase with grid voltage. This paper proposes a new kind of method to solve the problem effectively. Firstly various kinds of control algirithms used in photovoltaic grid-connected inverter are compared, and then the function between duty cycle and several measurable variables such as grid voltage and current error is generated. Based on this function a complete method to produce PWM control signals under Takagi-Sugeno fuzzy controller is proposed. This method adopts 4-input and 2-output structure. Four variables of grid voltage, current error, reference current and its differential are taken as input. After processed under Takagi-Sugeno fuzzy controller, control signals of the four switches are obtained as output. Via anti-fuzzy interface duty cycles of the two groups of control signals are achieved. At the end of this paper the principle of a single phase full-bridge inverter is illustrated. Through simulation analysis it can be seen that compared with traditional hysteresis control the proposed method has advantages in terms of low switch frequency, simple hardware structure, small THD and so on. It feeds power to the utility with unity power factor.