Abstract
In order to achieve the low cost and high performance control of three-phase PWM rectifier, a direct power control (DPC) strategy based on a new-style virtual flux-linkage observer is proposed. The model of three-phase PWM rectifier and the principle of virtual flux-linkage vector control are introduced firstly. Then, in order to avoid the effect of integral initial value and cumulative deviation, three first-order low-pass filters are cascaded to replace the pure integral link; an improved virtual flux-linkage observer of three-phase power grid is presented. From the observed virtual flux-linkage, the voltage and instantaneous power of three-phase power grid are online estimated. On this basis, the power grid voltage sensorless direct power control system of three-phase PWM rectifier is designed. Simulation results have shown that, both in the rectifying state and in the inverting state, the power grid side current and the DC side voltage of three-phase PWM rectifier all can be effectively controlled; the high power factor operation of three-phase PWM rectifier is realized.
Highlights
Compared with the conventional uncontrolled rectifier using diodes, adopting three-phase PWM rectifier, the energy can be controlled to freely flow along positive and negative directions [1, 2]
The AC current and DC voltage sensors play a crucial role in ensuring the control performance of three-phase PWM rectifier system
According to the topology construct of three-phase PWM rectifier, the AC side voltage uk can be expressed by the DC side voltage and switching functions
Summary
Compared with the conventional uncontrolled rectifier using diodes, adopting three-phase PWM rectifier, the energy can be controlled to freely flow along positive and negative directions [1, 2]. In the conventional virtual fluxlinkage observer, there exists a pure integral link, and the estimation process of virtual power grid flux-linkage is inevitably affected by the initial value and the cumulative deviation of the integrator [2, 20,21,22,23]. About the direct power control (DPC) of three-phase PWM rectifier without power grid voltage sensor, preliminary research progress has been made [24, 25]; the integral initial value and cumulative deviation of pure integrator remain to be solved. Based on the improved virtual flux-linkage observer, the power grid voltage sensorless DPC strategy of a three-phase PWM rectifier is proposed. Simulation results have verified the validity and feasibility of the proposed control strategy
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