Comprehensive vector modulation method of three-phase diode clamping three-level converter

Abstract

The invention relates to a comprehensive vector modulation method of a three-phase diode clamping three-level converter. The comprehensive vector modulation method comprises the following steps of: judging a sector where an output vector is, then judging whether the current output vector is in a linear modulation region or an overmodulation region, and calculating the duty ratio of an IGBT (Insulated Gate Bipolar Transistor) of each phase of bridge arm according to a conventional SVPWM (Space Vector Pulse Width Modulation) method or a virtual vector synthesis SVPWM method in the linear modulation region; and in the overmodulation region, calculating the duty ratios of large vectors and medium vectors according to an overmodulation algorithm, decomposing the medium vector according to the following principles: even if the action time of one medium vector is equal to the sum of one third of respective total action time of two large vectors adjacent to the one medium vector plus one third of the total action time of the medium vector, and finally calculating the duty ratio of the IGBT of each phase of bridge arm. The comprehensive vector modulation method disclosed by the invention can not only realize overmodulation of an NPC (Neutral Point Clamping) three-level converter by virtue of three-level output and also can furthest restrict larger offset and larger fluctuation of DC neutral-point voltage caused by overmodulation.

Description

technical field [0001] The invention relates to an operation control technology of a wind power generation system, in particular to a comprehensive vector modulation method for a three-phase diode-clamped three-level converter. Background technique [0002] Among the existing three-phase converter control methods, the voltage space vector SVPWM modulation technology has a higher DC voltage utilization rate than the SPWM modulation technology, and the generated waveform has high quality, low harmonic content, and is convenient for digital signal processors. Real-time control and other advantages have been widely used. Regardless of the two-level converter or the multi-level converter, the working area of ​​the SVPWM is divided into a linear modulation area and an over-modulation area. In the overmodulation area, overmodulation technology must be used to achieve higher DC voltage utilization, that is, to output excessive AC voltage under the same DC voltage. [0003] At pres...

AI Technical Summary

Problems solved by technology

At this time, since there is no short vector and the medium vector acts for a long time, large midpoint voltage fluctuations will occur at this time

[0015] The reason why it is difficult to implement the overmodulation technology of three-level converters is that when three-phase diode-clamped (NPC) three-level converters realize overmodulation, one of the basic vectors of the synthesized output vector must be a large vector and the other is a medium vector. Vector, a large vector has no effect on the fluctuation of the midpoint voltage, but a medium vector will cause the offset and fluctuation of the midpoint voltage, and at this time there is no other control vector that can adjust the midpoint voltage, so that the midpoint voltage during overmodulation volatility is difficult to control

It can be seen that this overmodulation technique uses a large number of neutral vectors 210, which increases the action time of the neutral vector relatively, and there are no other vectors that can adjust the neutral point voltage, so that the neutral point voltage shifts and fluctuates, which is not practical

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