Feedback Linearization-Based Direct Power Control for the Modular Multilevel Converter

The cascaded linear control structure is usually adopted in the modular multilevel converter (MMC). This paper proposes a direct power control method based on feedback linearization, in order to improve the power tracking accuracy and dynamic responses of MMC. First, the control signals in the AC and DC paths are taken as the input variables while the AC output power and the circulating currents are taken as the output variables. The multiple-input multiple-output (MIMO) nonlinear model of MMC is established and linearized based on the feedback linearization technique. Then, the linear controllers in the AC and DC paths can be designed according to the control targets of the new linearized system, and the direct power control method is proposed. With the feedback linearization equations, the final control signals of the MMC can be derived. Finally, because some variables cannot be observed, the characteristic equations of these variables are established, and the zero-dynamics stability of the proposed control method is discussed on the basis of stability analysis theory. The experiments are conducted to verify the proposed method. With the proposed method, higher tracking accuracy and smaller tracking errors of the active and reactive power can be observed in the steady-state operation condition;faster active power dynamic responses and smaller reactive power fluctuations can be observed in the active power step operation condition;faster reactive power dynamic responses and smaller active power fluctuations can be observed in the reactive power step operation condition. These results indicate that this method can effectively control the active and reactive power of the MMC and has a higher power tracking accuracy and faster dynamic response. © 2021, Editorial Board of Journal of Tianjin University(Science and Technology). All right reserved.