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| Model-Free Predictive Voltage Control Strategy for LC-Filtered Voltage Source Inverter |
| Yin Zheng1, Hu Cungang1, Rui Tao2, Feng Zhuangzhuang1, Lu Geye3 |
1. School of Electrical Engineering and Automation Anhui University Hefei 230601 China;
2. School of Internet Anhui University Hefei 230601 China;
3. State Key Lab of Security Control and Simulation of Power Systems and Large Scale Generation Equipment Tsinghua University Beijing 100084 China |
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Abstract This paper proposes a model-free predictive voltage control strategy for LC-filtered voltage source inverters to solve the problem that the prediction error increases when the parameters of conventional model predictive control are mismatched. The strategy establishes a look-up table based on the double gradients of voltage and current. By calculating and storing the voltage and current gradients under the action of the application vectors at the previous time, combined with the sampling values at the current time, the voltage and current at the future time can be predicted. The state space prediction equation is further reconstructed. The gradient value of the unapplied vector is updated according to the voltage and current gradients under the action of the applied vector. The voltage and current cost functions evaluate and select the optimal vector in the next control period. This method is independent of system parameters and simple, which can eliminate the stagnation of gradient updating in the conventional model-free prediction and improve the output voltage performance. Finally, simulation and experiment verify the effectiveness and superiority of the proposed method.
Firstly, the look-up table of the capacitor voltage gradient and the inverter-side current gradient is designed. Based on the gradient information, the voltage and current can be predicted without parameters. Secondly, the proposed method reconstructs the state-space prediction equation to ensure real-time updates of all gradients in each control period, eliminating the stagnation phenomenon of conventional model-free predictive control. In addition, the output voltage quality is further improved using the cost function with two control targets. Finally, the effectiveness of the proposed method is verified by experiments.
Simulation results on the voltage-current gradient updating show that the root mean square error (RMSE) of the conventional updating method is 6.91 V, and the RMSE of the proposed model-free predictive voltage control (MFPVC) updating method is 3.66 V, which is 3.25 V lower than that of the conventional updating method. Experimental results on the accurate model parameters show that the proposed method can achieve similar voltage performance with the conventional model predictive voltage control (MPVC). Experimental results on the inaccurate model parameters show that when the controller parameter mismatches the actual parameter, the proposed MFPVC produces smaller prediction errors than the conventional MPVC. Hence, the parameter robustness of the proposed MFPVC can be verified.1231223The following conclusions can be drawn from the simulation and experimental analysis: (1) The proposed method has good parameter robustness. When the parameters change, the output voltage error of the inverter is significantly reduced, the voltage quality is improved, and the voltage performance is similar to that of MPVC under the condition of accurate parameters. (2) This method proposes an advanced voltage and current gradient updating method, which can update the voltage and current gradient under all vectors in real time, eliminate the stagnation phenomenon and the predicted spikes, and further improve the output voltage quality.
In future studies, the proposed method can be extended to the LCL filter type VSI, or the voltage ripple can be further reduced by vector combination.
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Received: 27 September 2022
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2023, Vol. 38 
