Control for grid-connected bi-directional AC-DC converters in parallel operation

In this paper, the problem of inconsistent power flow direction in parallel multiple modular bi-directional AC-DC converters with conventional control method is analyzed. The inherent relationship between system operating status and the trend of the dc bus voltage is researched, and an improved control strategy for the modular bi-directional AC-DC converters in parallel operation is proposed. The consistent power flow of each module is achieved by utilizing a combined inversion and rectification dc bus voltage regulators. Power flow of inversion and rectification is distinguished naturally by different dc bus voltages. At the same time, the seamless switching between inversion and rectification is realized. The stability of the modular AC-DC converter parallel system is analyzed in detail with the design principle of the key parameter given. A prototype is built and both of the steady-state and transient experimental results are presented to verify the effectiveness of the proposed system and control method.