Current limit control method and current limit control device of three-level inverter

Abstract

The invention discloses a current limit control method and a current limit control device of a three-level inverter. The current limit control device comprises a current limit control unit, an auxiliary switching tube switch-on unit and a main switching tube switch-on unit. The current limit control method includes: S1, when currents outputted by a bridge leg are larger than or equal to a current limit threshold value, switching off two main switching tubes and then switching off two auxiliary switching tubes; S2, when the currents outputted by the bridge leg are decreased to be smaller than the current limit threshold value, enabling the two auxiliary switching tubes to act according to normal switching logic; S3, when the currents outputted by the bridge leg are decreased to be smaller than the current limit threshold value and effective edges of PWM (pulse-width modulation) signals of the main switching tubes or auxiliary switching tubes are reached, enabling the two main switching tubes to act according to the normal switching logic. By the current limit control method and the current limit control device, time for mutual energy infusion and mutual charging of positive and negative buses is shortened, overvoltage of the unilateral bus is avoided, frequent actions of the main switching tubes are avoided, the switching tubes are protected, and output voltage waveforms are improved.

Description

technical field [0001] The present invention relates to the field of electronic technology, more specifically, to a current limiting control method and device for a three-level inverter. Background technique [0002] The inverter is an important part of the Uninterruptible Power System (UPS), and its reliability directly determines the stability of the UPS operation. Current limiting technology is a very important protection technology of the inverter, which can effectively protect the power switching elements and improve the impact resistance of the inverter when the inverter is suddenly overloaded or the output is short-circuited. The existing current limiting technology generally detects the inductor current (the current flowing through the power switching element), compares the detected inductor current with the set threshold, and generates a limit when the inductor current exceeds the set threshold. Current protection signal, the power switching element is turned off b...

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Problems solved by technology

That is to say, the energy charged by the positive busbar to the inductance during normal wave generation will continue to flow to the negative busbar to charge the negative busbar (when the circuit works in the negative half cycle of the output voltage, the situation is opposite), which will cause positive (negative) During the frequency cycle, the positive busbar continues to output energy to the negative busbar (or vice versa), resulting in excessive voltage of the unilateral busbar, thereby increasing the risk of damage to the switch tube

Instead of wave-by-wave current limiting, four switch tubes may be fully sealed several times in a PWM wave near the current limiting point. The larger inductor current makes the phenomenon of positive and negative bus mutual injection more serious.

[0010] It can be seen that in the existing current limiting technology, the wave-by-wave current limiting method has the defects of output voltage waveform difference and positive and negative bus energy mutual injection; although the non-wave-by-wave current limiting method has a better output voltage waveform, the positive and negative Mutual irrigation of bus energy may be more serious, and the risk of overvoltage on unilateral bus is high, which increases the risk of damage to the switch tube

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