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Method for solving selected harmonic eliminated switching angle of ladder wave multilevel converter

A technology of specific harmonic elimination and switching angle, applied in the direction of converting AC power input to DC power output, electrical components, output power conversion devices, etc., can solve the problems of slow convergence, accelerated convergence, and large amount of calculation, Achieve the best performance, increase the number of switching angles, and strong practicability

Active Publication Date: 2014-10-08
CHINA UNIV OF MINING & TECH (BEIJING)
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Problems solved by technology

[0009] Regarding the solution of SHE equations, numerical methods (such as Newton iterative method, homotopy algorithm, etc.) or random search algorithms (such as genetic algorithm, swarm intelligence algorithm, etc.) The solution process depends heavily on the selection of the initial value. A suitable initial value can greatly speed up the convergence speed, otherwise it will converge very slowly or even diverge. However, there is no systematic and effective method for the selection of the initial value.
Moreover, the SHE equations are likely to have multiple local extreme points, and the local optimal solution obtained by numerical algorithm or random search algorithm cannot be guaranteed to be globally optimal, so the performance of the converter cannot be guaranteed to be optimal.
In recent years, solving methods based on algebraic theory (such as knot elimination method, Wu method, etc.) have been proposed. Such methods do not need to give initial values ​​and can give all solutions of SHE equations. The maximum number of points is 5. For the case of more switching points, the final result cannot be given due to the large amount of calculation.

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  • Method for solving selected harmonic eliminated switching angle of ladder wave multilevel converter
  • Method for solving selected harmonic eliminated switching angle of ladder wave multilevel converter
  • Method for solving selected harmonic eliminated switching angle of ladder wave multilevel converter

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specific Embodiment 1

[0032] Specific embodiment 1: each step in the solution method is described in detail in combination with a step-wave multilevel converter with switching points N=3.

[0033]For a three-phase ladder-wave multilevel converter with N=3, its SHE equations are:

[0034] (Formula 4)

[0035] where 0 1 2 3 < π / 2, the value range of the modulation ratio m is generally 0 < m < 3. In practice, the value of m is generally given in advance. Here we might as well take m = 2 as an example for illustration.

[0036] Step S1: According to the cosine function multiple angle formula:

[0037] (Formula 5)

[0038] (Formula 6)

[0039] Substitute (Equation 5) and (Equation 6) into (Equation 4), and let , the harmonic elimination equations are transformed into the following polynomial equations:

[0040] (Formula 7).

[0041] Step S2: When N=3, the definition of the elementary symmetric polynomial is:

[0042] ...

specific Embodiment 2

[0068] Specific embodiment two: when N=5, the order of harmonics that the three-phase ladder wave converter needs to eliminate is the 5th, 7th, 11th, and 13th harmonics. Therefore, in addition to the fundamental wave equation, the SHE equations also need to order 5, The amplitudes of the 7th, 11th, and 13th harmonics are zero, a total of 5 equations.

[0069] Step S1: According to the cosine function multiple angle formula and variable substitution Transform the original SHE equations into polynomial equations ,in .

[0070] Step S2: put Converted to a system of polynomial equations about elementary symmetric polynomials ,in for about Elementary symmetric polynomials of .

[0071] Step S3: Let the modulation ratio m = 3.5, according to have to , substitute , and calculate in pure lexicographic order Under the Groebner basis, the system of equations transforms into , where the first equation is The unary high-degree polynomial equation of ,...

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Abstract

The invention relates to a method for solving the selected harmonic eliminated switching angle of a ladder wave multilevel converter. Power reduction is performed on an equation set by use of an elementary symmetric polynomial, and the equation set is triangularized by use of a Groebner basis algorithm; the solution of a multivariate higher-order polynomial equation set is converted into the solution of two univariate higher-order polynomial equations and a set of single-variable linear equations; all solutions of a harmonic elimination equation set can be obtained based on constraint conditions; and the optimal switching angle can be worked out by evaluating the total harmonic of each set of solutions. Compared with the current commonly-used numerical algorithm and random search algorithm, no initial value needs to be given, and all solutions of the harmonic elimination equation set can be obtained. Compared with other existing algebraic algorithms, the amount of calculation is greatly reduced, more switching angles can be processed, and the method has higher practical values.

Description

technical field [0001] The present invention relates to the field of power electronic systems and control methods thereof, in particular to control and harmonic elimination methods for inverters and multilevel converters, and in particular to a method for Selective Harmonic Eliminated (SHE) ) solution method of switching angle. Background technique [0002] Specific Harmonic Elimination (hereinafter referred to as SHE) modulation is different from traditional waveform modulation PWM technology, it is a method to obtain the switching angle by solving equations. Compared with sinusoidal pulse width modulation technology, SHE modulation has the characteristics of low switching frequency, small switching loss and high waveform quality. Due to the elimination of low-order harmonics, the remaining harmonics are mostly concentrated in high frequencies, which can greatly reduce the requirements for filters. In addition, higher voltage gains can be obtained to save energy. like fi...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H02M7/483H02M1/12G06F17/12
Inventor 杨克虎
Owner CHINA UNIV OF MINING & TECH (BEIJING)
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