A voltage sensorless control of low-complexity model predictive direct power control (LC-MPDPC) for pulse width modulation (PWM) rectifier is proposed. The conventional LCMPDPC adopts one or two voltage vectors during one control period, which achieve good steady-state performance and quick dynamic response. Besides, based on the mathematical model of the real system, the conventional method only requires one prediction to find the optimal voltage vector, which reduces the control complexity and computational burden. However, the use of one or two vectors during one sampling interval present abundant current harmonics and high power ripples. In order to solve these problems, whilst preserving all the advantages of conventional LC-MPDPC, this paper presents a novel control scheme, with the aim of operating at a constant-switching frequency and obtaining an excellent steady-state performance at a low switching frequency. The proposed method is based on an optimal application of three voltage vectors in a symmetrical way, which takes advantage of advanced pulse width modulation techniques. Furthermore, the virtual flux based control scheme is introduced to achieve voltage sensorless control. The proposed strategy is compared with the conventional MPDPC methods and its effectiveness is confirmed by both simulation and experimental results from a three-phase PMW rectifier under 1000-W operation condition.

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.

An improved state estimation algorithm based on branch current is put forward to revise leverage-point measurements with gross errors in distribution systems. Using the inherent characteristic of leverage-point measurement, this method introduces structure robust factors into the objective function of the weighted least absolute value (WLAV) estimator for weakening the masking effect of bad leverage-point measurements. Meanwhile, a new approach is proposed to deal with voltage-magnitude measurements on the branch-current-based state estimation so that it can increase the measurement redundancy and the estimation precision, and enhance the observability. An analysis is done for the IEEE 123-bus systems and the tested results show the advantages of each one of new ideas.