Four-level converter voltage balance modulation method

Abstract

The invention discloses a four-level converter voltage balance modulation method. For a four-level converter without flying capacitors, the present invention converts the intermediate capacitor C through a PI regulator 2 The voltage U C2 Control is 1 / 3U dc , while the capacitance C 1 and C 3 The voltage U C1 and U C3 auto-balancing, thus achieving three capacitors C 1 、C 2 、C 3 The voltage balance of NNPC‑4L and TNNPC‑4L four-level converters with flying capacitors, on the basis of the proposed voltage balance method for four-level converters without flying capacitors, two Modulation method, and the voltage balance control of the flying capacitor is realized by selecting the redundant switch state, which can achieve a better voltage balance effect even under low frequency conditions; for the HC‑4L converter with flying capacitors, in the On the basis of the proposed four-level converter voltage balance method without flying capacitors, the result is redundant switch states, which realize the voltage balance control of DC bus capacitors and flying capacitors, and have better performance even under low frequency conditions. voltage balancing effect.

Description

technical field [0001] The invention relates to the field of voltage balance control, in particular to a voltage balance modulation method for a four-level converter. Background technique [0002] Multi-level converters are widely used in medium-voltage and high-power fields, mainly including three-level converters, five-level converters, cascaded multi-level converters, etc., while four-level converters are relatively less used. This is mainly because the voltage balance control of an MLC with an even number of levels is more difficult to implement than that of an MLC with an odd number of levels. Moreover, the voltage unbalance problem of a four-level converter without flying capacitors is more difficult to solve than that of a four-level converter with flying capacitors. [0003] Up to now, the four-level converter topology without flying capacitor mainly includes neutral point clamped four-level converter I (Neutral Point Clamped Four-Level Converter, NPC-4L-I, such as ...

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Problems solved by technology

Among them, for the NNPC-4L converter, there is currently a simplified virtual space vector modulation method, which not only overcomes the problem of capacitor voltage imbalance, but also reduces the voltage ripple of the flying capacitor under low-frequency conditions, but the algorithm is relatively complicated. It is not easy to implement in engineering; for HC-4L converter, there is currently a method of injecting zero-sequence voltage and carrier phase-shift modulation, which can realize the balanced control of DC bus capacitance and flying capacitor, but this algorithm cannot reduce the capacitance Voltage low-frequency ripple limits the application of HC-4L converter in the field of motor control

[0006] Based on the above analysis, the four-level converter without flying capacitors has not been widely used. The reason is that the DC bus capacitor voltage balance problem is not easy to solve. Although some scholars have proposed a corresponding voltage balance algorithm, there is a large amount of calculation. large, the switching frequency is not fixed, and the logic judgment is complicated, etc.

However, the four-level converter with flying capacitors has low-frequency voltage fluctuations, which limits its application in motor control and other fields.

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