Abstract
A novel strategy of three-vector-based model predictive direct power control (MPDPC) is proposed for three-phase Pulse-width Modulation (PWM) rectifier. Under ideal grid conditions, three-vector MPDPC is studied, and a good control effect has been achieved. However, under the unbalanced power grid condition, the traditional control strategy has some problems, such as a high harmonic content of current and large instantaneous power pulsation. A new three-vector model predictive control is proposed based on the new instantaneous power theory, and the objective function is established by instantaneous power error. The duty cycle of the selected vector is calculated by solving the optimal objective function. Under an unbalanced power grid, this paper takes a three-phase PWM rectifier as a research object, and carries out simulation and experimental tests on the traditional and new control strategies. The experimental results show that the new control strategy has lower current harmonics, and eliminates the twice grid-frequency oscillation of the grid in instantaneous power.
Highlights
In the discrete mathematical model of Pulse-width Modulation (PWM) rectifier, the model predictive control (MPC) predicts the grid side current, instantaneous power and other electrical quantities in the control cycle; the objective function is set according to the needs of the control system, an optimal voltage vector is obtained by solving the optimal objective function [1,2,3,4,5,6]
The objective function of FCS-model predictive direct power control (MPDPC) is composed of the error term between the instantaneous power and the given value, and an appropriate voltage vector is selected by solving the optimal objective function, which improves the control performance of the rectifier while maintaining a fast dynamic response
When the instantaneous active power output of rectifier has no pulsac2 tion component, the instantaneous reactive power output has no pulsation component, which can realize the new instantaneous power are constant under the condition of unbalanced power grid
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The objective function of FCS-MPDPC is composed of the error term between the instantaneous power and the given value, and an appropriate voltage vector is selected by solving the optimal objective function, which improves the control performance of the rectifier while maintaining a fast dynamic response This method uses one voltage vector in a switching cycle. In reference [19], a three-vector FCS-MPDPC is proposed, which uses two non-zero vectors and one zero-vector This algorithm has the advantages of high sinusoidal current, small instantaneous power ripple and the switching frequency is fixed. Different from reference [19], the algorithm needs to predict the instantaneous power under 12 different vector combinations, and sets an objective function, based on the global power error, that is, to accumulate the sum of squares of the instantaneous power error terms in each switching action in a control cycle.
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