In this study, an improved direct power control strategy based on the deadbeat current control with adaptive ability is proposed for three-phase distribution static compensator (DSTATCOM), whose current references are directly computed by power reference and power feedback according to the instantaneous power theory, and the deadbeat current control is used to assure the current waveform quality. The improved direct power control strategy does not need phase-locked loop, and not exists the coupling among the control variables of DSTATCOM. Moreover, the proposed control strategy has good dynamic response and adaptive ability, and its design process is very simple. At last, the feasibility and validity of the proposed control strategy are verified by the simulation and experiment results.

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This study presents an improved dead-beat control method for three-phase pulse-width modulation rectifier of the switching power supply under source-voltage harmonics and unbalance disturbances. First, a reference currents extraction method and an active negative sequence currents injection method for the dead-beat control are presented to suppress the input harmonic currents and the second harmonic voltage of the DC-link voltage in the rectifier. Then, active disturbance rejection control is presented to substitute for the PI control, which can improve the transient response and strengthen the antidisturbance ability of the rectifier. Finally, to improve the efficiency of the power supply, two auxiliary inductors are introduced to realise soft switching of the DC/DC converter, which is an idea of taking the rectifier and the DC/DC converter as a whole. The feasibility and superior performances of the presented control methods and topology have been validated by the experimental results.

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This paper intends to comparatively study the stabilities of grid-connected inverters with three closely related controllers: quasi-proportional resonance (quasi-PR), proportional integral (PI), and proportional resonance (PR) under the weak grid. Firstly, considering the influence of frequency coupling characteristic, a frequency coupling admittance model of quasi-PR controlled inverter is established. Then, the admittance characteristics of the quasi-PR, PI and PR controlled inverters are compared. Admittance characteristics of the PI and PR controlled inverters are similar while the quasi-PR controlled inverter is quite different: the amplitude of the quasi-PR controlled inverter is larger than that of the PI controlled inverter and the phase difference between the two inverters is obvious in the mid-high frequency areas, which are mainly caused by the resonance bandwidth of the quasi-PR controller. Furthermore, the stabilities of the quasi-PR, PI and PR controlled inverters are analyzed. The stabilities of the PI and PR controlled inverters are similar but the quasi-PR controlled inverter is more sensitive to weak grid and high inverter output power. To achieve the same system stability, the voltage outer-loop bandwidth of the quasi-PR controlled inverter should be designed narrower than that of the PI and PR controlled inverters. Finally, experiments verify the correctness of the analyses.