Real-time voltage-sharing method for cascaded transverter

Abstract

The invention provides a real-time voltage-sharing method for a cascaded transverter. According to the invention, before m pulse combinations are transmitted to each module, in the current AD period, a controller first finds out and sequences modules with the highest DC voltage and modules with the lowest DC voltage from the current controlled modules, as well as pulse combinations mostly discharging a module DC-side capacitor and pulse combinations mostly charging the module DC-side capacitor; and the controller swaps the modules with the highest DC voltage and the pulse combinations mostly discharging the module DC-side capacitor according to the sequencing, as well as the modules with the lowest DC voltage and the pulse combinations mostly charging the module DC-side capacitor according to the sequencing. The real-time voltage-sharing method has the advantages of simple arithmetic, high voltage-sharing speed and high precision.

Description

technical field [0001] The invention relates to a pressure equalization method for cascaded converters, in particular to a real-time pressure equalization method for cascaded converters. Background technique [0002] The cascaded converter is a circuit form in which multiple sub-converters are cascaded to form a high-voltage converter. It is the most frequently used technical route for high-voltage and large-capacity power electronic devices. Converters are developing rapidly, such as half-bridge cascaded converters, H-bridge cascaded converters, modular multilevel converters, transformer-based cascaded converters, and so on. Some of these converters are used for high-voltage frequency conversion, some are used for reactive power compensation, some are used for flexible DC transmission, and some are used for grid power flow control. [0003] Regardless of the specific topology of the cascaded converter, each sub-converter used for cascading is usually called a "module". Ea...

AI Technical Summary

Problems solved by technology

For the above method (1), its advantage is that the algorithm is simple and the overhead is very low; however, it only adjusts the DC voltage once every power frequency cycle, and the voltage equalization speed is very slow, often requiring tens of milliseconds or even several seconds ; Moreover, regardless of the pressure equalization situation, the pulses are rotated mechanically according to a certain rule, which sometimes helps to equalize the pressure, and sometimes aggravates the imbalance, making it difficult to achieve good pressure equalization accuracy

For the above method (2), its advantage is that it can perform voltage equalization control in real time; however, as the number n of cascaded modules increases, the algorithm overhead also increases significantly, and the difficulty of implementation increases; in addition, the voltage equalization speed The accuracy and accuracy are also limited by the characteristics of the PI regulator, and the voltage equalization adjustment process is prone to overshoot and oscillation, and the voltage imbalance is aggravated during the transient process, endangering the operation of the module