Hybrid MMC sub-module capacitor voltage bidirectional equalization topology

Abstract

The invention provides a bi-directional balanced hybrid MMC topological structure based on a diode clamping circuit. The bi-directional balanced hybrid MMC topological structure is composed of n / 2 half-bridge sub-modules, n / 2 full-bridge sub-modules and n-1 additional series devices. The topology is explained by taking five-level hybrid MMC topology as an example. The topology is composed of two half-bridge-type modules, two full-bridge-type modules and three additional units. The additional unit connected between the HBSMs is the same as the additional unit connected between the HBSM and the FBSM. Each unit comprises two parallel branches. A branch circuit 1 only comprises a diode, a branch circuit 2 is formed by reversely connecting the diode and a switch in series (an IGBT and a reverse parallel diode), and the inductor is connected to a common branch circuit of the branch circuit 1 and the branch circuit 2. In the additional unit connected between the FBSMs, the branch circuit 1 and the branch circuit 2 have the same structures, and each of the branch circuit 1 and the branch circuit 2 consists of a series diode, an inductor and a switch (an IGBT and an anti-parallel diode). Compared with a traditional software voltage balance method, the topology mainly has the two advantages that firstly, a control framework is simplified, a voltage balance control link is omitted, and control resources are saved; and secondly, the number of voltage sensors is reduced, the complexity of the control system is reduced, and the communication pressure is reduced. In addition, compared with other hardware voltage balance circuits, the topology not only can realize bidirectional balance, but also reduces the number of inductors in the circuit, and effectively reduces the hardware cost.

Description

technical field [0001] The invention belongs to the technical field of power electronics flexible direct current transmission, and relates to a hybrid MMC sub-module capacitor voltage bidirectional equalization topological structure, which only uses a simple hardware circuit to realize the bidirectional equalization control of the capacitor voltage. Background technique [0002] With the development of medium and high voltage inverters, a series of stringent requirements are put forward for high-power inverters. Modular multilevel converter (MMC) has the advantages of modularity, scalability, and high fault tolerance. Therefore, MMC is considered to be the most attractive topology in HVDC, VSC, APF, STATCOM, and energy storage systems. [0003] However, the capacitor voltage imbalance seriously threatens the reliable operation of MMC-based HVDC. The capacitor voltage imbalance is caused by non-ideal drive pulses of the sub-modules (SMs) during the system-controlled pre-cha...

AI Technical Summary

Problems solved by technology

However, these methods introduce the feed-forward of the capacitor voltage in the modulation, which reduces the voltage utilization of the modulated wave; for the second category, although the software balancing method has flexibility and wide application, due to the number of voltage sensors, additional Computational burden and signal delays due to sampling and transmission are still disadvantages of software balancing methods; in order to reduce the number of voltage sensors and reduce the effect of control delays, hardware balancing methods are becoming more and more popular

Therefore, it is the most feasible solution to achieve balance control topology through an external balance control circuit, but the current external balance topology can only achieve unidirectional voltage balance

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