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| Extended Direct Power Model Predictive Control for Reduced Matrix Converter Under Unbalanced Grid Voltage Operation Condition |
| Han Sipeng, Song Weizhang, Xu Shaojie, Li Jiageng, Du Xiaobin |
| School of Electrical Engineering and Automation Xi'an University of Technology Xi'an 710048 China |
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Abstract Aiming at the abnormal condition of unbalanced grid voltage, the grid side of RMC has double frequency power pulsation. The active and reactive power in RMC cannot track the power reference value at the same time, whose pulsation cannot also be eliminated using the instantaneous reactive power control strategy of traditional direct power prediction, thus leads to current distortion in grid side and instability in DC side. The topology of RMC is different from the three-phase PWM rectifier because a high-frequency transformer is used to couple the front and rear stages. The method is not applicable completely. Therefore, the problem of larger pulsation it must be solved. In order to solve the above problems, this paper proposes an extended direct power predictive control method in an RMC system.
Firstly, the double frequency fluctuation expressions of active and reactive power under unbalanced input voltage are derived and analyzed. The positive and negative sequence components of grid voltage and current are extracted by using the quarter grid cycle delay method. Secondly, an extended instantaneous power theory more suitable for unbalanced power grid is introduced, and a model predictive extended power control method is proposed. By reconstructing the reference value of instantaneous power, the self-suppression of grid side power and DC voltage ripple fluctuation is realized. Then, aiming at the problem that the input active power still contains large pulsation when the extended power predictive control under unbalanced grid voltage, the adjacent two-beat error of the active power is added to the cost function on the minimum cost function of the model predictive control to reduce the error of active power tracking. The new cost function is constructed to suppress the input active power pulsation and suppress the grid side current distortion under unbalanced grid voltage conditions. Finally, the effectiveness of proposed method was verified in an RMC experimental prototype.
A comparative experiment between the traditional direct power predictive control method and the proposed extended direct power predictive control method is designed. The experimental results show that the active power double frequency fluctuation amplitude of direct power predictive control under unbalanced grid voltage is 5.8 V, the reactive power fluctuation amplitude is 6 V, the fluctuation amplitude is 7.4 V, and the grid current THD is 7.41 %. Under the extended power predictive control, the active power fluctuation amplitude is 4 V, the fluctuation amplitude is reduced by 31.03 %, and the reactive power fluctuation amplitude is 5.8 V, the fluctuation amplitude is reduced by 3.33 %. The output voltage fluctuation amplitude is 5.4 V, and the fluctuation amplitude is reduced by 27.03 %. The sinusoidal grid side current and unit power factor operation of RMC are realized, which verifies the effectiveness and correctness of the proposed method. This paper draws the following conclusions : (1)Under unbalanced grid conditions, the proposed method can effectively suppress the fluctuation of input current, output power and output DC voltage caused by unbalanced grid voltage. (2) The complex weighting factor selection is not required for the cost function using proposed method. (3)The power factor in grid side is closer to unity comparing the direct power predictive control.
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Received: 09 January 2023
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2023, Vol. 38 
