Modular multi-level converter capacitor voltage fluctuation passive control method

Abstract

The invention relates to a modular multi-level capacitor voltage fluctuation passive control method. The method comprises the following steps of 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 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 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, free of singular points 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 modular multilevel converter control, in particular to a passive control method for capacitor voltage fluctuations of a modular multilevel converter. Background technique [0002] Modular Multilevel Converter (MMC) has been widely used in large-scale renewable energy due to its advantages of low harmonic content, low switching loss, strong fault ride-through capability, easy modular expansion and industrial production. On-grid field. 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. The voltage fluctuation of the MMC capacitor will inevitably increase the loss of the converter, resulting in a deviation in the output voltage of the AC side, which will affect the reliable operation of the sys...

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Problems solved by technology

However, due to the intermittent and fluctuating characteristics of large-scale renewable energy power generation, it is easy to cause energy imbalance between three-phase MMC phases, which in turn leads to unbalanced sub-module capacitor voltages.

The voltage fluctuation of the MMC capacitor will inevitably increase the loss of the converter, resulting in a deviation of the output voltage on the AC side, which 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, which is aimed at the nonlinearity of the MMC sub-module capacitor voltage fluctuation system The essence of controller design is not from the perspective of energy, so when there are uncertain disturbances, the immunity and robustness of the vector controller will face insurmountable challenges

Compared with the traditional vector control method, the existing technology adopts the nonlinear control method to design a controller that can reflect the nonlinear nature of the MMC sub-module capacitor voltage fluctuation system from the perspective of energy, and the stability and robustness of the closed-loop control system On the one hand, the control performance has been improved, but the calculation of this method is more complicated, and the problem of excessive internal loss of the system is not solved, and there is still insufficient energy optimization, which is not conducive to solving practical engineering problems

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