Virtual space vector modulation method and system for neutral point clamped multi-level converter

Abstract

The invention discloses a virtual space vector modulation method and system for a neutral point clamped multi-level converter. The method comprises the following steps that a preset virtual switch state is adopted, the multi-level space vector pulse width modulation PWM is simplified into virtual space vector pulse width modulation PWM; a three-level space vector pulse width modulation PWM algorithm is adopted, so as to obtain a plurality of voltage vector sequences and the vector action time of the synthesized reference vectors in the virtual space vector pulse width modulation PWM; the optimal voltage vector sequence closest to the current in the target midpoint in the plurality of voltage vector sequences is screened so as to control the voltage balance of the upper and lower capacitorson a bus; and a three-level space vector pulse width modulation PWM algorithm is adopted to obtain the action time of the optimal voltage vector sequence so as to calculate the actual switch state and action time of each phase. According to the method, the control is simple, and the bus capacitor voltage balance control in the full modulation ratio and the full power factor range of the neutral point clamped multi-level converter can be easily realized.

Description

technical field [0001] The invention relates to the technical field of multilevel converters, in particular to a virtual space vector modulation method and system for a midpoint clamped multilevel converter. Background technique [0002] Neutral-Point Clamped (NPC) three-level converter has been widely used in industry due to its simple structure and few components, especially suitable for power conversion occasions of 3.3kV and below. Steel rolling, offshore wind power and other fields have been widely used. However, when the number of levels increases to four levels and above, there is a problem that the bus midpoint voltage is difficult to balance, which limits its application in higher voltage applications. Such as figure 1 As shown, the diode-clamped midpoint-clamped multilevel converter has a DC bus consisting of n identical capacitors connected in series. If the voltage of each capacitor is E, it can output 0, E, 2E, ... ...nE has n+1 levels in total. The difficul...

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Problems solved by technology

However, the multi-level space vector PWM with more than three levels has a large number of triangular sectors. On the one hand, it is necessary to judge the sector where the reference vector is located and perform corresponding calculations. On the other hand, when using redundant vectors to realize the balance control of bus capacitance To switch between different vectors to ensure the least number of switching actions, not only the amount of calculation is large, but also the programming is extremely complicated

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