A Voltage Sensorless Robust Control Scheme for LCL Grid-Connected Inverters Based on GESO Approach

The traditional current control of the LCL grid-connected inverters often requires additional sensors for resonance damping, harmonic suppression and grid synchroniza-tion. A single current sensor control scheme is presented in this article to reduce the number of sensors and the risk of sensor failure on the basis of maintaining the similar performance as the traditional dual sensor control. The proposed control scheme is based on a generalized extended state observer (GESO) used to estimate the equivalent disturbance, while the estimation is used for disturbance rejection and phase-locked loop (PLL) synchroni-zation. Aiming at the problem of current overshoot at startup time of sensorless strategy, a voltage pre-estimation strategy is propos-ed to reduce the current overshoot phenomenon. In addition, a low-pass filter is added to the current tracking loop to improve the system adaptability for grid impedance. Then the system is equivalent to three loops for the stability analysis and the parameter constraints of the controller are given. Moreover, it was found that the parameters in GESO are smaller than the nominal parameters of the inverter, which could improve the robust stability of the system. Finally, the effectiveness and feasibility of the proposed control scheme are verified through the experimental tests.
Note to Practitioners
—The state observer has been used in this paper to estimate the voltage and disturbance of the grid, which are used to control the grid-connected current and suppress the disturbance. The proposed method not only can reduce the number of sensors and improve the robust stability of the system, but also can reduce the risk of power grid instability caused by sensor failure on the premise of ensuring similar performance to traditional dual sensors. It ensures the stable operation of the power grid, and has a certain significance for expanding to the three-phase gr id-connected system.