Modular multilevel converter grid-connected current passive consistency control method

Abstract

The invention relates to a modular multilevel grid-connected current passive consistency control method. The method comprises the following steps of: establishing MMC grid-connected current under the condition of unbalanced power grid voltage, and designing an expected global energy function of an MMC grid-connected system so as to obtain a PCHD model of the MMC grid-connected system under the condition of unbalanced power grid voltage; based on the PCHD model of the MMC grid-connected system, with a consistency method adopted, constructing an MMC grid-connected passive consistency controller based on the PCHD model under the condition of unbalanced power grid voltage so as to obtain a control quantity; processing the control quantity by adopting a pulse modulation method to obtain a corresponding trigger pulse signal; and controlling the switching state of a converter of each phase of bridge arm sub-module of the MMC according to the trigger pulse signal. Compared with the prior art, the method combinesthe PCHD model and the consistency method to realize independent synchronous control of MMC grid-connected positive and negative sequence subsystems, is simple in control law form, free of singular points and good in stability, and can effectively improve a grid-connected current synchronous tracking effect.

Description

technical field [0001] The invention relates to the technical field of modular multilevel converter control, in particular to a passive consistency control method for grid-connected current of a modular multilevel converter. Background technique [0002] Modular Multilevel Converter (MMC) is a multilevel converter that can realize high-voltage and medium-voltage power conversion without a transformer. MMC has been widely used in the field of large-scale renewable energy grid connection. However, when a single-phase short circuit occurs in the power grid, the AC current of the system will generate negative sequence components, which will cause power oscillations, which will eventually affect the stable operation of the MMC grid-connected system, and even cause system instability in severe cases. [0003] Therefore, it is necessary to control the MMC grid-connected current to achieve MMC grid-connected current balance. Traditional vector control methods are mostly used for con...

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Problems solved by technology

[0002] Modular Multilevel Converter (MMC) is a multilevel converter that can realize high-voltage and medium-voltage power conversion without a transformer. MMC has been widely used in the field of large-scale renewable energy grid connection. However, when a single-phase short circuit occurs in the power grid, the AC current of the system will generate negative sequence components, which will cause power oscillations, which will eventually affect the stable operation of the MMC grid-connected system, and even cause system instability in severe cases

[0003] Therefore, it is necessary to control the MMC grid-connected current to achieve MMC grid-connected current balance. Traditional vector control methods are mostly used for control. This method is designed for the nonlinear nature of the MMC grid-connected current system. From the perspective of energy, the immunity and robustness of the vector controller face challenges when there are uncertain disturbances; compared with traditional vector control methods, the existing technology is based on nonlinear Starting from the above, design a controller that can reflect the nonlinear nature of the MMC grid-connected current system. This method can improve the stability and robustness of the closed-loop control system to a certain extent. The internal correlation of the negative sequence current subsystem affects the dynamic tracking performance of the passive control, so the synchronization of the positive and negative sequence independent subsystem control cannot be ensured, and the synchronous and stable tracking of the positive and negative sequence systems cannot be reliably realized.

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