The power control stability of grid connected vector control based voltage source converters(VSCs)is studied. VSC regulates the active and reactive power injected into the grid by controlling the d and q axis current oriented to the grid voltage vector

respectively. The relationships between the power and the regulated current are instrumental for the stability of the power control. The power and current relationship in the simplified system of VSC connected to the infinite bus through grid impedance is studied. It has been found that

as the grid gets weaker

the sensitivity of active power to d axis current becomes negative. As a factor that threatens the power control stability

the negative sensitivity is further studied. Approaches to improve the power control stability of VSC connected to a weak grid are proposed. This work is supported by Fundamental Research Funds for the Central Universities (No. 163111006).