Converter arm, series high voltage DC transformer and control method

Abstract

The present application provides a converter arm, a series-connected high-voltage DC transformer, and a control method. The head end of the converter arm is connected to the DC positive pole, the tail end is connected to the DC negative pole, and the middle point leads out as the AC end of the converter arm. The converter arm includes at least one energy consumption unit and at least one voltage equalizing unit; capacitor, the first power semiconductor device, and the third power semiconductor device and the fourth power semiconductor device connected in series, and the other end of the third power semiconductor device is connected to the connection between the third power semiconductor device and the fourth power semiconductor device of the adjacent voltage equalizing unit point or energy consumption unit; one end of the first DC capacitor is connected to the connection point of the third power semiconductor device and the fourth power semiconductor device, one end of the first power semiconductor device is connected to the other end of the first DC capacitor, and the other end of the first power semiconductor device is connected to the first power semiconductor device. At the other end of the four power semiconductor devices, the first power semiconductor devices of all the voltage equalization units are connected in series in the same direction.

Description

technical field [0001] The application relates to the technical field of power electronics, in particular to a commutation arm, a series high-voltage DC transformer and a control method. Background technique [0002] High-voltage DC transformers are usually used in the field of DC transmission or DC power distribution, and are used to connect DC ports of different voltage levels. [0003] With the development of modern power electronics technology, due to the relatively limited withstand voltage level of single-tube power semiconductor devices, their application and development are greatly restricted. [0004] The power semiconductor devices can be composed of sub-modules, and then the sub-modules can be cascaded to form a converter arm, and the converter arm can form an isolated DC transformer or a non-isolated DC transformer through different combinations. Therefore, whether it is an isolated or non-isolated DC transformer, the converter arm is a key component unit that p...

AI Technical Summary

Problems solved by technology

In the application of DC transformers, once the converter arm is subjected to overvoltage, or a single sub-module is subjected to overvoltage, it will cause damage to the device, and the expansion of the fault will lead to the failure and damage of the entire converter arm

[0005] In the prior art, there is a method of adding device connections between modules, such as the patent CN105406722A diode clamp power switch connected in series with a high-voltage DC transformer. The method of the above comparison document is to use diodes to establish a charging and discharging channel between the DC capacitors of the sub-modules , using the auxiliary circuit to form a closed loop between the sub-modules between the bridge arms to achieve the function of DC voltage balance, but the total energy of the converter cannot be consumed, it just flows between the sub-modules of the converter

The disadvantages of the above methods are: first, the energy brought by the overvoltage cannot be consumed and can only be transferred between modules. When the overvoltage is serious, the total energy cannot be consumed and the equipment will still be damaged; second, the entire Once a fault occurs in the middle part of the closed-loop system, the entire closed-loop system will be disconnected, and energy will accumulate in the sub-module where the converter arm is disconnected, resulting in overvoltage damage to the sub-module and low reliability.

[0006] Since it is impossible to solve the problem of short-term overvoltage under fault conditions, in order to make the whole commutation arm withstand higher short-term overvoltage, we can only increase the capacitance value of the sub-module, or increase the number of sub-modules, which greatly increases the Cost and area occupied by the entire converter arm

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