On control of the grid-connected inverter (GCI) with LCL filter, the inverter-side current model predictive control is adopted conventionally. The ultimate grid-side current is controlled indirectly by control of inverter-side current. The ideal scenario is that grid-side current is directly controlled. However, the conventional control model is complicated and the calculation is heavy. This study proposed a novel direct grid-side current model predictive control (GSC-MPC) for GCI with LCL filter. Based on timing coordination of both forward and backward difference methods, a direct connection is established between the grid-side output current and the inverter-side output voltage. Meanwhile, a proper mathematical model is built for an improved model predictive control. The exact required voltage vector in the next sampling interval is predicted and calculated by this model. The output optimal voltage vector is modulated by space vector pulse width modulation technique to control the inverter. Furthermore, the proposed GSC-MPC is rather robust to parameter variation. Simulation and experimental results present that the proposed GSC-MPC can improve the current control performance effectively for GCI with LCL filter.

Compared with traditional single L-type filters, LCL filters for three-phase grid-connected inverters can suppress the switching voltage and current ripple better, thus reducing harmonic pollution to the power grid. However, the increase in system order also makes it difficult to control the system. To solve the problems of complex model and severe coupling of LCL filter in the d-q coordinate system, the decoupling control of current inner loop by the linear extended state observer (LESO) was proposed based on the analysis of mathematical model of grid-connected inverter with an LCL filter. Moreover, given the relatively low speed of system response in traditional active disturbance rejection control (ADRC), the tracking differentiator (TD) was removed, and the nonlinear control law was replaced with the PI controller. Compared with the conventional feedforward decoupling method, the reasonably designed LESO used in this work can not only realize decoupling control of the original system to improve its performance, but also save the cost of sensor and achieve a better decoupling effect. The effectiveness of the proposed current control strategy was verified by experimental results.

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