Capacitor voltage fluctuation suppression method for modular multilevel converter

Abstract

The invention relates to a capacitor voltage fluctuation suppression method for a modular multilevel converter (MMC). The method comprises the following steps: establishing an MMC fluctuation capacitor voltage state equation based on a PCHD model; based on the established MMC fluctuation capacitor voltage state equation, further constructing to obtain an MMC capacitor voltage fluctuation passive consistency controller based on a PCHD model so as to obtain a fluctuation capacitor voltage control quantity; processing the fluctuation capacitor voltage 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 passive consistency control method based on the PCHD model is used for suppressing the capacitor voltage fluctuation of the MMC, has the advantages of being simple in control law form, small in mean deviation and good in stability, and can effectively suppress the capacitor voltage fluctuation of the MMC.

Description

technical field [0001] The invention relates to the technical field of control of modular multilevel converters, in particular to a method for suppressing fluctuations in capacitor voltage of modular multilevel converters. Background technique [0002] Modular Multilevel Converter (MMC) is composed of multiple sub-modules (Sub-module, SM) cascaded with the same structure. Type and double clamp type sub-module type three. MMC has the advantages of less harmonic content, low switching loss, strong fault ride-through capability, and is convenient for modular expansion and industrial production. It has been widely used in the field of large-scale renewable energy grid connection. However, due to the intermittent and fluctuating characteristics of large-scale renewable energy power generation, it is easy to cause the energy imbalance between the three-phase MMC phases, which in turn leads to the unbalanced capacitor voltage of the sub-modules, and the fluctuation of the MMC capa...

AI Technical Summary

Problems solved by technology

However, due to the intermittent and fluctuating characteristics of large-scale renewable energy power generation, it is easy to cause the energy imbalance between the three-phase MMC phases, which in turn leads to the unbalanced capacitor voltage of the sub-modules, and the fluctuation of the MMC capacitor voltage will inevitably increase the loss of the converter, resulting in AC Deviation of the output voltage on the side will affect the reliable operation of the system in severe cases

[0003] Therefore, it is necessary to suppress the fluctuation of MMC capacitor voltage. The traditional method is to use the vector control method. This method is designed for the nonlinear nature of the MMC sub-module capacitor voltage fluctuation system. Since it is not from the perspective of energy, when When there are uncertain disturbances, the disturbance immunity and robustness of the vector controller will face insurmountable challenges; compared with the traditional vector control method, the existing technology uses a nonlinear control method to start from the energy point of view, Designing a controller that can reflect the nonlinear nature of the MMC sub-module capacitor voltage fluctuation system improves the stability and robustness of the closed-loop control system. Big problems, there are still deficiencies in energy optimization, which is not conducive to solving practical engineering problems

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