DC-link current estimation for load-side converter of brushless doubly-fed generator in the current feed-forward control

In the stand-alone brushless doubly-fed generator (BDFG) control system, there are two back-to-back converters composed of the machine-side converter (MSC) and the load-side converter (LSC). The LSC is a three-phase AC-DC pulse width modulation converter which usually adopts the double-loop control strategy with outer voltage loop and inner current loop. The introduction of the DC-link current feed-forward for improving the dynamic performance of the LSC can reduce the effect of the load disturbance to the system. However, the DC-link current has a complex harmonic spectrum with the MSC connected to the DC side, so its average value is not convenient to measure. This study presents a DC-link current estimation algorithm for the current feed-forward control in the LSC of the stand-alone BDFG. With the help of the equivalent circuit of the BDFG and the power balance, the rapid calculation of the average DC-link current can be estimated as well. With this estimation of the current instead of the actual DC-link current, the DC-link voltage and AC side current of the LSC can achieve stability quickly. The effectiveness and correction is validated by the simulation and experiments.