2results about How to "Improve on-grid performance" patented technology

This invention provides a method and system for balancing the midpoint potential of a three-level, three-phase, four-wire modular inverter. The method includes: designating one of multiple inverter modules connected in parallel with AC / DC buses as a midpoint potential adjustment module, and the rest as non-midpoint potential adjustment modules; the midpoint potential adjustment module acquires the positive and negative DC bus voltages and calculates the voltage difference between them, performs filtering and closed-loop control calculations on this voltage difference to generate a midpoint potential compensation control quantity, and injects this control quantity as a zero-sequence compensation component into a modulation signal to generate a drive signal to adjust the DC bus midpoint potential; the non-midpoint potential adjustment modules do not participate in the midpoint potential compensation control, but only perform zero-sequence current control. This invention achieves midpoint potential balancing in a three-phase, four-wire inverter without the need for an external hardware balancing circuit, solves the midpoint potential adjustment conflict problem in multi-module AC / DC parallel scenarios, effectively suppresses zero-sequence circulating current, and improves system operational stability.

The application provides a kind of permanent magnet direct drive wind turbine multi-objective control method under power grid asymmetrical fault, solve the technical problem of power fluctuation suppression and current unbalance degree reduction control target coordination optimization in fault ride-through. Including the following steps: S1: establish the positive and negative sequence coordinate system model of permanent magnet direct drive wind turbine grid-side converter, separate the positive and negative sequence of grid-side converter voltage and current;S2: calculate the grid-side converter reference current instruction of three control targets;S3: construct the unified expression form of grid-side converter reference current;S4: select active power fluctuation suppression and negative sequence current suppression as the coordinated optimization control target for control;S5: construct multi-objective optimization function, obtain the converter current reference value, and carry out current closed-loop control on grid-side converter. The beneficial effects of the application are: the multi-objective coordinated optimization control of permanent magnet direct drive wind turbine under power grid voltage fault is realized, and the low voltage ride-through capability and grid-connected performance are enhanced.