Three-level space vector modulation method under multiple coordinate systems

Abstract

The invention relates to a three-level space vector modulation method under multiple coordinate systems and relates to a three-level space vector modulation method applied to a middle / high-voltage inverter and a photovoltaic inverter, and a control system thereof. The control system comprises a power grid interface, a voltage-increasing device, a bus capacitor with a neutral point, a power switch device, a clamping diode, a main control system, a driving system and a three-phase load, and the power switch device form a three-phase bridge arm. The three-level space vector modulation method comprises the following specific operation steps of: a, virtually simulating a middle vector of a three-level space vector on the premise of taking an average value of a neutral point current as zero during a switch period; b, respectively calculating a coordinate of a basic vector including a virtual middle vector in coordinate systems of 30 degrees, 60 degrees, 90 degrees, 120 degrees and 150 degrees; and c, judging sector areas according the characters of a reference voltage space vector in each coordinate system. The three-level space vector modulation method under the multiple coordinate systems has the advantages of small calculation amount, capability of simply and conveniently realizing the level balance of the three-level neutral point, and suitability for multi-level space vector modulation of more than three levels.

Description

Technical field: [0001] The invention relates to a three-level space vector modulation method and its control system applied to medium and high voltage frequency converters and photovoltaic inverters, in particular to a multi-coordinate system-based three-level space vector modulation method and its pulse generation mechanism . Background technique: [0002] Since the voltage applied to the power switching tube is only half of that of the traditional two-level inverter, the neutral point clamped (NPC) three-level inverter is very suitable for medium and high voltage variable frequency drive applications. , NPC three-level inverters are also gradually applied to the field of low-voltage drives due to their ability to output better voltage and current waveforms (low harmonic content, low electromagnetic interference) than two-level inverters. [0003] One of the main problems of the NPC three-level inverter is that its neutral point voltage is easy to shift. Under certain con...

AI Technical Summary

Problems solved by technology

[0005] Through the analysis, it can be seen that the medium vector and small vector in the 27 basic vectors will have an impact on the neutral point, and the impact of the positive small vector and the negative small vector on the neutral point potential of the inverter is just opposite, it is based on this characteristics, the current method of controlling the neutral point potential of the three-level NPC inverter is realized by adjusting the action time of the positive and negative small vectors, but when the inverter operates at a high modulation degree, the medium vector The action time will play a dominant role, and the fluctuation or offset of the neutral point potential cannot be controlled only by adjusting the positive and negative small vectors. The influence of the neutral point potential is zero, and the condition of this method is that the algebraic sum of the three-phase current output by the inverter is zero. After the virtual neutral vector, the six large sectors divided by the large vector will be divided separately into five small sectors, adding up to a total of 30 sectors, no matter which sector the reference voltage space vector falls in, the three nearest basic space vectors will effectively control the inverter through a certain action time and sequence The neutral point potential, but the disadvantage of this method is that the judgment of the sector is very complicated, and it also increases the complexity of other parts of the NPC three-level space vector modulation algorithm

Images