Abstract：With the rapid development of distributed energy resources (DERs), LC-filtered voltage source inverters (VSI) have become an essential interface to connect the DERs with the grid due to their harmonic suppression capability and cost advantages at high power levels. In order to regulate the output performance of LC-filtered VSI with small voltage ripples and low total harmonic distortion (THD), model predictive control (MPC) has been widely investigated for its simple implementation, fast response, and multi-objective control. However, the direct use of discrete system models makes MPC prone to mismatches in system parameters, which increases prediction error and endangers system stability. The model-free predictive control (MFPC) methods utilize the sampled signals instead of system parameters to construct the predictive model of VSI. The sixteen current gradients generated by the eight basic voltage vectors (VVs) are calculated and stored in the look-up tables (LUTs) in each control period. Future state predictions can be obtained based on the current gradients, eliminating the impact of parameter mismatch on the prediction calculation. This paper proposes a model-free prediction and parameter-less reference-based triple-vector predictive control (PLR-TV-MFPC) for LC-filtered VSI, considering the parameter dependency of the reference calculation. The triple vectors can improve the output performance of VSI and reduce the THDs of output voltage. The durations of applied vectors are calculated based on the ratios of their cost functions. Then, the inverter-side current gradients and capacitance voltage gradients of applied VVs can be obtained by analyzing the gradients corresponding to different VVs in different control periods. The gradients of the remaining VVs are summarized into two cases, where the components on the α-axis and β-axis are equal. The gradients updating equations are constructed, and the stagnation effect can be eliminated. Furthermore, the phase-amplitude relationship is analyzed with $\Delta \theta_{\mathrm{f}}^{\mathrm{ref}}$ and $\Delta \theta_{\mathrm{f}}$ as the phase difference between the reference and sample signals of inverter-side current and capacitance voltage. The reference of inverter-side current can be obtained, and the system parameters are eliminated. Finally, the proposed method is evaluated on the LC-filtered VSI experimental platform. The output voltage’s THD is 3.82 % and 1.59% using the conventional and the proposed methods. Under different load conditions, TV-MPC’s THD and prediction error are 0.89 V and 1.04%, and the proposed PLR-TV-MFPC’s are 1.56 V and 1.59%. The proposed PLR-TV-MFPC has a low and stable prediction error of 1.72 V when the system parameters of LC-filtered VSI mismatch from the actual values; the conventional TV-MPC and TV-MFPC vary from 1.4 V to 16.4 V and 2.2 V to 9.8 V, respectively. Conclusions can be drawn as follows. (1) Using triple vectors and the update of all gradients in each control period can reduce the output voltage prediction error and THD of LC-filtered VSI. The output performance of the proposed method is similar to that of the conventional TV-MPC under accurate parameters. (2) The proposed PLR-TV-MFPC is robust against parameter mismatch. When the system parameters are inaccurate, the proposed method’s output voltage prediction errors and THD keep a low and stable value, verifying the effectiveness of the proposed model-free prediction and parameter-less reference methods. The proposed method can be extended to the LCL-filtered VSI in future studies or further tested under grid-tied conditions.
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2025, Vol. 40 
