A Discontinuous Pulse Width Modulation Method for Three-level Converter
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A technology of pulse width modulation and converter, which is applied in the direction of converting AC power input to DC power output, electrical components, climate sustainability, etc., and can solve problems such as reducing three-level converters
Active Publication Date: 2020-01-10
合肥庐阳科技创新集团有限公司
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[0010] In fact, in the existing research, the two problems of reducing the common-mode voltage and controlling the neutral point voltage of the three-level converter are separated, and there are few researches that solve these two problems comprehensively
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Embodiment 1
[0077] This embodiment provides a discontinuous pulse width modulation method for a three-level converter that reduces the common-mode voltage and eliminates the DC offset of the midpoint voltage, such as figure 1 shown, including the following steps:
[0078] Step S1: Acquire with voltage sensor figure 2 The upper capacitor voltage u on the DC side of the three-level converter mentioned in C1 , Lower capacitor voltage u C2 , three-phase output phase voltage u a , u b and u c and three-phase output current i a i b and i c , judge the magnitude of the three-phase output phase voltage, and get the maximum voltage u max =max(u a , u b , u c ), intermediate voltage u mid =mid(u a , u b , u c ) and minimum voltage u min =min(u a , u b , u c ); Use the collected three-phase output current to predict the phase current i′ of the next switching cycle a , i′ b and i′ c And judge the size, get the maximum current i′ max =max(i' a ,i' b ,i' c ), intermediate cur...
Embodiment 2
[0113] Taking the reference vector falling in the overlapping area of PB1 and NB2 as an example, first calculate the respective midpoint currents
[0114] The midpoint current in PB1 mode is obtained according to the phase current rearranged in the next cycle:
[0115] i NP,PB1 =(2-u max + u mid )i' mid +(2-u max + u min )i' min
[0116] Midpoint current in NB2 mode:
[0117] i NP,NB2 =(2-u max + u min )i' max +(u mid -u min )i' mid
[0118] Midpoint voltage Δu NP = u C2 -u C1 >0 if i NP,PB1 and i NP,NB2 are greater than zero, the clamping mode with the maximum midpoint current should be selected to restore the midpoint voltage as soon as possible; if i NP,PB1 and i NP,NB2 different sign, the clamping mode with positive midpoint current should be selected to recover the midpoint voltage as soon as possible; if i NP,PB1 and i NP,NB2 are both less than zero, the clamp mode with the minimum absolute value of the midpoint current should be selected so tha...
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Abstract
The invention relates to a discontinuous pulse width modulation method for a three-level converter that reduces the common-mode voltage and eliminates the DC offset of the midpoint voltage. Firstly, the three-phase voltage and the three-phase current of the three-level converter are collected for preprocessing , reorder the three-phase voltages, and use the three-phase currents to predict the phase currents of the next switching cycle and reorder them, and then get all possible clamping modes according to the rearranged phase voltages, according to the rearranged phase currents of the next cycle Calculate the mid-point current, and determine the clamping mode according to the mid-point voltage control rule to control the mid-point voltage. During the modulation process, the common-mode voltage is reduced by abandoning the basic vector with high common-mode voltage, and finally according to the clamping The duty cycle model of the mode calculates the modulation wave and compares it with the carrier type determined in the clamp mode to generate a specific PWM switching sequence. The modulation method proposed by the invention can not only effectively control the balance of the midpoint voltage, but also reduce the switching loss of the system.
Description
technical field [0001] The present invention relates to a modulation method of a three-level converter, and more specifically relates to a new type of discontinuous pulse width modulation capable of reducing common-mode voltage, reducing switching loss and eliminating midpoint voltage DC side offset at the same time method. Background technique [0002] With the development of power electronics technology, three-level converters have the advantages of low total harmonic distortion, low device voltage stress and high energy conversion efficiency, and are widely used in various fields but often accompanied by midpoint voltage shift , Switching loss and other issues. [0003] The midpoint voltage control is a key technical issue of the three-level converter. The offset and fluctuation of the midpoint voltage will not only cause the quality of the output voltage and current of the converter to decrease, but in serious cases, it will even cause the DC side capacitor to overvolta...
Claims
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