A Unified Method for Specific Harmonic Cancellation in Multilevel Converters
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A specific harmonic elimination and multi-level technology, applied in the direction of converting AC power input to DC power output, electrical components, output power conversion devices, etc.
Active Publication Date: 2019-01-22
CHINA UNIV OF MINING & TECH (BEIJING)
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[0013] The present invention aims to solve the defect that different switching modes need to be processed separately for SHE modulation of the current multi-level converter, and proposes a unified solution method for switching angles in all switching modes
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specific Embodiment 1
[0052] Embodiment 1: a multilevel converter with switching angle N=4 and modulation ratio m=3 eliminates the 5th, 7th and 11th harmonics.
[0053] The specific harmonic elimination equations with 4 switching angles and a modulation ratio of 3 are established as follows:
[0054]
[0055] Let the value range of the switch angle be 0 to 180°, and use the particle swarm algorithm to solve the equations, and obtain a set of solutions as follows:
[0056]
[0057] Due to θ 1 ,θ 2 ,θ 3 are less than 90°, mark its state as a rising edge, θ 4 Greater than 90°, use 180°-θ 4 =62.9°replacement, and mark its state as a falling edge at the same time, will replace the θ after 1 ,θ 2 ,θ 3 ,θ 4 Arranged in ascending order of their size relationship together with their status as follows:
[0058]
[0059] The arrows indicate the switching mode at the switching angle, the upper arrow indicates the rising edge, and the lower arrow indicates the falling edge, and the correspondi...
specific Embodiment 2
[0060] Embodiment 2: Select a multilevel converter with a switching angle of N=4 and a modulation ratio of m=2 to eliminate the 5th, 7th and 11th harmonics.
[0063] Use the triangular multiple formula and variable substitution x i =cosα i Transform equation (11) into the following polynomial equations:
[0064]
[0065] Use elementary symmetric polynomials:
[0066]
[0067] Perform variable substitution and simplification on Equation (12), the simplification can be done by using the SymmetricReduction command in the symbolic calculation software Mathematics, and the following about e 1 ,e 2 ,e 3 ,e 4 equation set:
[0068]
[0069] solve p 1 (e)=e 1 -2=0 to get e 1 = 2, and e 1 bring p 2 ,p 3 ,p 4 , the following equations are obtained:
[0070]
[0071] Calculate the reduced Groebner basis of the pure lexicographical order of the three polynomials in formula (15) (the three polynomials can...
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Abstract
The invention discloses a unified method for eliminating a selective harmonic wave of a multi-level converter. For all possible switch modes of a multi-level converter, only one harmonicelimination equation set needs to be solved; a constraint condition related to a switch angle relation is removed, so that the solution process is simplified; and a switch mode corresponding to a final solution result can be recovered automatically according to a solved distribution zone. Compared with the traditional a multi-level converter selective harmonic wave elimination method needing to solve an equation set for each switch mode, the method disclosed by the invention has the following beneficial effects: all possible switch modes and corresponding switch angles can be solved once, so that the harmonic elimination equation set solution success probability in practical application can be improved substantially; and more switch angels that can be realized physically can be provided, thereby realizing optimized controlling of a multi-level converter.
Description
technical field [0001] The invention relates to the field of power electronic systems and control methods thereof, in particular to a unified calculation method for switching angles in various switching modes on the problem of eliminating specific harmonics of multilevel converters. Background technique [0002] Multilevel converters can use low withstand voltage devices to achieve high voltage and high power output. They have the advantages of high output waveform quality, less harmonic content, low electromagnetic interference, and small voltage change rate. They have received extensive attention in recent years. In AC motors Drives, distributed renewable energy generation systems, static synchronous var compensators and other fields have been widely used. Due to the limitation of switching frequency in high-power applications, the use of traditional carrier PWM modulation will generate a large number of low-order harmonics, which seriously affects the safe and stable oper...
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