Cascaded converter and protection method thereof

Abstract

The invention provides a cascaded converter and a protection method thereof. A discharge loop and a bypass circuit are added into the converter, and simultaneously, an active voltage equalizing method or an overvoltage protection method is used for monitoring the converter to ensure that the direct-current bus voltage of each transformer in the cascaded converter is in a balanced state, or the overvoltage protection is performed when the voltage is overhigh. In the invention, the active voltage equalizing method obtains a good effect through tests. In the invention, the overvoltage protection method and the active voltage equalizing control method adopt the same circuit, a fast protection method is provided, a good protection effect can be obtained, the failure-free operation time of a system is prolonged, and a foundation is provided for the application of the cascaded converter. The invention has important significance for the application of cascaded converters in the future.

Description

Technical field: [0001] The invention relates to the field of power electronics, in particular to a cascade converter and a protection method thereof. Background technique: [0002] The cascade converter consists of N independent full-bridge circuits or half-bridge circuits connected in series on the AC side, and the DC sides are independent of each other. A three-phase system can be formed by 3 bridge arm pairs through Y-shaped or △-shaped connection. Used in various high-voltage power electronic devices. This cascaded converter has many advantages: each converter unit has the same structure, which is easy to achieve modular design, installation, and maintenance; the DC side is independent of each other, and it is easier to achieve module voltage equalization compared with topological structures such as device series; The converter unit works symmetrically and the switching load is balanced; after cascading, low-voltage components can be used to achieve high-voltage output, co...

AI Technical Summary

Problems solved by technology

For cascaded converters, the voltage equalization method is mainly aimed at the normal operation of the converter, that is, the voltage equalization control strategy in the unlocked state; for the blocked standby state, a single converter unit is in an uncontrollable rectification state, and there is still a lack of Effective Pressure Equalization Method

[0005] Moreover, when the start-up time is long or the standby state is long, the DC bus voltage imbalance of each converter unit will gradually increase over time, which may exceed the normal operating range of the components and cause damage to the components, or affect the converter. normal operation of the unit

[0006] There are various overvoltage protection strategies currently available, and their specific implementation uses the inverter bridge of the converter unit. In order to maintain the stability of the entire system, when the voltage deviation of the converter unit is large, there may be too long response time or If the adjustment speed is not fast enough and other problems, when a single converter unit has an overvoltage fault, the entire system can only be withdrawn

For the overvoltage protection of a single converter unit, when a single converter unit cannot continue to work due to overvoltage problems, only the entire system is blocked and exited, and the system is too frequently exited, for the application of cascaded inverters very unfavorable

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