| 摘要 |
A method and a system for controlling the mains bridge of a four-quadrant PWM frequency converter provided with a direct-voltage intermediate circuit when power is flowing into the supply network, and in which method
- a virtual three-phase network having the same frequency with the actual supply network is created,
- when power is flowing into the supply network, the power semiconductor switches are controlled on the basis of the voltages of the virtual network,
- the supply network phase currents are measured, and
- based on the curve form of the measured phase currents, inferences are made as to whether the virtual network is correctly synchronized with the supply network and, if necessary, the phase shift of the virtual network is corrected so as to keep it synchronized with the supply network.
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