Abstract：Voltage source converter（VSC）connected to weak AC power grid has the risk of small disturbance

instability. Under the traditional control strategy，VSC has to reduce output power to maintain stable operation. In

order to improve the stability of the weak grid connected VSC system，first established a universal analysis model

for revealing the stability mechanism of weak grid connected VSC based on the AC voltage outer loop，and

revealed the influence of the coupling characteristics among the phaselocked loop（PLL）and the VSC outer loop

control on system stability. On this basis，a parameter adaptive control strategy for virtual parallel point was

proposed. The detailed switch model of VSC in the PSCAD/EMTDC environment verifies the effectiveness of the

proposed control method.

      Key words：voltage source converter（VSC）；weak AC power grid；small disturbance stability；improved

control strategy