Novel control strategy for voltage source converters based on energy function

This paper proposes a nonlinear control strategy for pulse-width modulated voltage source converters (VSCs). A passivity-based approach, resulting from the Lyapunov direct method, is presented for designing an effective nonlinear VSC controller to improve their dynamic behaviors under perturbed conditions. The differential equations of the converters are obtained and then transformed into a d - q frame. Considering the nonlinearity of the transformed equations, the Lyapunov direct method is utilized to find a solution to improve the transient response. The time derivative of the Lyapunov function guarantees that increasing its dissipative term will result in the trajectory of the VSC system returning to the equilibrium point more quickly. The proposed control strategy can be simultaneously applied to multiVSC devices, such as a unified power flow controller (UPFC). Moreover, it is shown that the proposed strategy meets the steady-state requirements without using any other control loop. As an example, a 3-machine system with a UPFC is studied to verify the effectiveness of the proposed strategy.