CN103078479B - Control method for canceling specified harmonics of three-level midpoint clamp photovoltaic inverter - Google Patents

Abstract

The invention discloses a control method for canceling specified harmonics of a three-level midpoint clamp photovoltaic inverter. The control method comprises the following steps of: firstly, establishing a mathematical model of the control method for the specified harmonics of the three-level midpoint clamp photovoltaic inverter and solving the following nonlinear transcendental equations; secondly, establishing a midpoint current mathematical model of the three-level midpoint clamp photovoltaic inverter; and thirdly, solving by adopting a continuous space ant colony algorithm. According to the control method disclosed by the invention, the control method for canceling the specified harmonics of the three-level midpoint clamp photovoltaic inverter is combined with midpoint voltage balance; the midpoint voltage balance can be effectively controlled while the specified low-order harmonics are canceled, so that an output waveform is greatly improved and the total harmonic distorsion is reduced.

Description

Three level neutral-point-clamped photovoltaic DC-to-AC converter particular harmonic eliminates control method

Technical field

The present invention relates to a kind of three level neutral-point-clamped photovoltaic DC-to-AC converter particular harmonic and eliminate control method.

Background technology

The particular harmonic of three level neutral-point-clamped photovoltaic DC-to-AC converter eliminates the optimum choice of control method by switching time, and the pwm voltage waveform of control inverter rightly, does not exist some specific (low order) harmonic wave in the voltage that inverter is exported.

The where the shoe pinches that particular harmonic eliminates control method is mainly to solve one group of Nonlinear and transcendental equations, traditional method adopts Newton iteration method, the method solves Nonlinear System of Equations needs one group of initial value, whether the whether suitable algorithm that directly determines that initial value is selected restrains, so choosing of initial value will as far as possible close to non trivial solution.Choosing of initial value does not have system, effective method, and researcher generally adopts the method trying to gather, and efficiency is very low.And traditional particular harmonic eliminates control method only from the angle eliminating specific low-order harmonic, does not consider the overall performance of photovoltaic DC-to-AC converter.Be directed to three level neutral-point-clamped photovoltaic DC-to-AC converter, then, while elimination particular harmonic, do not consider the key technical problem of three level neutral-point-clamped inverter---neutral point voltage balance problem.

Summary of the invention

The object of this invention is to provide one solve easily and fast, accurately three level neutral-point-clamped photovoltaic DC-to-AC converter particular harmonic eliminate control method.

The technical scheme realizing the object of the invention is that a kind of three level neutral-point-clamped photovoltaic DC-to-AC converter particular harmonic eliminates control method, comprises the following steps:

1. set up three level neutral-point-clamped photovoltaic DC-to-AC converter particular harmonic and eliminate control method Mathematical Modeling, solve following Nonlinear and transcendental equations:

$\left\{\begin{array}{c}{f}_1\left(\mathrm{\α}\right)=\frac{U_{\mathrm{sm}\left(1\right)}}{U_d/2}=\frac{4}{\mathrm{\π}}\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{(-1)}^{i+1}\cos \left({\mathrm{\α}}_i\right)=m\\ f_2\left(\mathrm{\α}\right)=\frac{U_{\mathrm{sm}\left(5\right)}}{U_d/2}=\frac{4}{5\mathrm{\π}}\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{(-1)}^{i+1}\cos \left({5\mathrm{\α}}_i\right)=0\\ \·\\ \·\\ \·\\ f_N\left(\mathrm{\α}\right)=\frac{U_{\mathrm{sm}\left(M\right)}}{U_d/2}=\frac{4}{\mathrm{M\π}}\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{(-1)}^{i+1}\cos \left({\mathrm{M\α}}_i\right)=0\end{array}\right.;$

U in formula _dfor DC side supply voltage, N is closed half-convergency number by taking away in 1/4 cycle, and switching angle should satisfy condition: $D:0<{\mathrm{\&alpha;}}_1<{\mathrm{\&alpha;}}_2<...<{\mathrm{\&alpha;}}_{n-1}<{\mathrm{\&alpha;}}_N<\frac{\mathrm{\&pi;}}{2};$

2. three level neutral-point-clamped photovoltaic DC-to-AC converter mid point electric current Mathematical Modeling is set up: at a sampling period T _sinterior current in middle wire can be expressed as:

$\begin{array}{c}{i}_{\mathrm{NP}}=i_{\mathrm{NP}\_\mathrm{Medium}}+i_{\mathrm{NP}\_\mathrm{Small}}\\ =T_M*\left[\begin{array}{ccc}{M}_a& M_b& M_c\end{array}\right]\&CenterDot;\left[\begin{array}{c}{i}_a\\ i_b\\ i_c\end{array}\right]+\left[\begin{array}{cc}{k}_0& k_1\end{array}\right]\&CenterDot;\left[\begin{array}{cc}{T}_{S0}& 0\\ 0& T_{S1}\end{array}\right]\left[\begin{array}{ccc}{S0}_a& {S0}_b& {S0}_c\\ {S1}_a& {S1}_b& {S1}_c\end{array}\right]\left[\begin{array}{c}{i}_a\\ i_b\\ i_c\end{array}\right]\end{array}$

; Work as i _nP=0 or i _nPwhen → 0, the mid-point voltage of three level neutral-point-clamped photovoltaic DC-to-AC converter reaches balance;

3. continuous space ant colony optimization for solving is adopted:

1. 2. following equation can be obtained with step by step: $\left\{\begin{array}{c}{g}_1\left(\mathrm{\&alpha;}\right)=4/\mathrm{\&pi;}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{(-1)}^{i+1}\cos \left({\mathrm{\&alpha;}}_i\right)-m=0\\ g_2\left(\mathrm{\&alpha;}\right)=4/5\mathrm{\&pi;}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{(-1)}^{i+1}\cos \left({5\mathrm{\&alpha;}}_i\right)=0\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ g_{n-1}\left(\mathrm{\&alpha;}\right)=4/\mathrm{N\&pi;}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{(-1)}^{i+1}\cos \left({\mathrm{N\&alpha;}}_i\right)=0\\ g_n\left(\mathrm{\&alpha;}\right)=i_{\mathrm{NP}}=0\end{array}\right.$

This equation group is interpreted as the optimization problem asking n target, that is:

$\mathrm{Min}:\left\{\begin{array}{c}{y}_1={\left(g_1\left(\mathrm{\&alpha;}\right)\right)}^2\\ y_2={\left(g_2\left(\mathrm{\&alpha;}\right)\right)}^2\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ y_{n-1}={\left(g_N\left(\mathrm{\&alpha;}\right)\right)}^2\\ y_n={\left(i_{\mathrm{NP}}\right)}^2\end{array}\right.$

According to Objective Programming principle, be a target by above n target unification, that is:

$\mathrm{Min}:y=-\frac{1}{1+{y_1}^2+{y_2}^2+...{y_n}^2}.$

Step 2. in, the switch function M that middle vector is corresponding _am _bm _cbe defined as:

Middle vector	M a	M b	M c
				pon	0	1	0
opn	1	0	0
				npo	0	0	1
nop	0	1	0
				onp	1	0	0
pno	0	0	1

The switch function S0 that small vector is corresponding _as0 _bs0 _cand S1 _as1 _bs1 _cbe defined as:

Small vector	S0 a	S0 b	S0 c	Small vector	S1 a	S1 b	S1 c
								poo/onn	1	0	0	ppo/oon	0	0	1
opo/non	0	1	0	opp/noo	1	0	0
								pop/nno	0	0	1	pop/ono	0	1	0

After have employed technique scheme, the present invention has following positive effect: the particular harmonic of three level neutral-point-clamped photovoltaic DC-to-AC converter is eliminated control method and is combined with neutral point voltage balance by (1) control method of the present invention, at the specific low-order harmonic of elimination simultaneously, effectively can control neutral point voltage balance, effectively can eliminate low-order harmonic, improve output waveform greatly, reduce total harmonic distortion.

(2) ant colony optimization algorithm application inverter particular harmonic is eliminated in solving of control method by the present invention, ant colony optimization algorithm when solving Nonlinear System of Equations unlike traditional Newton iteration method, its variation tendency not needing the initial value of solving equation and prediction to separate, its initial population produces at random, the computational speed of algorithm can be accelerated, be easy to realize On-line Control.

Accompanying drawing explanation

In order to make summary of the invention more easily be clearly understood, below according to specific embodiment also by reference to the accompanying drawings, invention is described in further detail, wherein

Fig. 1 is the solution locus figure of three-level photovoltaic inverter switch angle.

Fig. 2 is three-level photovoltaic inverter output line voltage waveform, DC capacitor voltage waveform and line voltage spectrum.

Embodiment

Three level neutral-point-clamped photovoltaic DC-to-AC converter particular harmonic eliminates control method, comprises the following steps:

1. set up three level neutral-point-clamped photovoltaic DC-to-AC converter particular harmonic and eliminate control method Mathematical Modeling:

The single-phase voltage waveform of three level neutral-point-clamped photovoltaic DC-to-AC converter meets 1/4 periodic symmetry, and by Dirichlet theorem, waveform can resolve into following fourier series:

$U_{\mathrm{AN}}\left(\mathrm{\&omega;t}\right)=\frac{A_0}{2}+\underset{n=1}{\overset{\&infin;}{\mathrm{\&Sigma;}}}[A_n\sin \left(\mathrm{n\&omega;t}\right)+B_n\cos \left(\mathrm{n\&omega;t}\right)]---\left(1\right)$

In formula

$A_n=\frac{2}{\mathrm{\&pi;}}{\&Integral;}_0^{\frac{\mathrm{\&pi;}}{2}}\frac{U_d}{2}\cos \left(\mathrm{n\&omega;t}\right)d\left(\mathrm{\&omega;t}\right)---\left(2\right)$

$B_n=\frac{2}{\mathrm{\&pi;}}{\&Integral;}_0^{\frac{\mathrm{\&pi;}}{2}}\frac{U_d}{2}\sin \left(\mathrm{n\&omega;t}\right)d\left(\mathrm{\&omega;t}\right)---\left(3\right)$

Due to symmetry (the waveform odd symmetry and right of phase voltage waveform axial symmetry), therefore only containing odd sine term harmonic wave, so

$\left\{\begin{array}{c}{A}_n=0\\ B_n=\left\{\begin{array}{c}0,n=\mathrm{even}\\ =U_{\mathrm{sm}\left(n\right)}=\frac{{2U}_d}{\mathrm{n\&pi;}}\underset{k=1}{\overset{N}{\mathrm{\&Sigma;}}}{(-1)}^{k+1}\cos \left(n{\mathrm{\&alpha;}}_k\right),n=\mathrm{odd}\end{array}\right.\end{array}\right.---\left(4\right)$

In above formula: U _dfor DC side supply voltage, N is closed half-convergency number by taking away in 1/4 cycle,

Switching angle should satisfy condition

$D:0<{\mathrm{\&alpha;}}_1<{\mathrm{\&alpha;}}_2<...<{\mathrm{\&alpha;}}_{n-1}<{\mathrm{\&alpha;}}_N<\frac{\mathrm{\&pi;}}{2}.$

Consider in three-phase photovoltaic inverter, Zero-pharse harmonic can export according to three-phase three-wire system and eliminate, so emphasis harmonic carcellation number of times is 5,7,11,13 in three-phase tri-level photovoltaic DC-to-AC converter application system ..., 6i-1,6i+1 (i=1,2,3 ...).

From (4) formula, the amplitude of each harmonic is switching angle α _ifunction, as long as suitably select α ₁, α ₂..., α _nvalue, just can make U _{sm (i)}=0, namely eliminate the harmonic wave that angular frequency is i ω.

If fundamental modulation degree eliminate 5,7,11 ..., 6i-1,6i+1 ... M subharmonic (M is eliminable most high order harmonic component number of times), obtains equation as shown in the formula (5).

$\left\{\begin{array}{c}{f}_1\left(\mathrm{\&alpha;}\right)=\frac{U_{\mathrm{sm}\left(1\right)}}{U_d/2}=\frac{4}{\mathrm{\&pi;}}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{(-1)}^{i+1}\cos \left({\mathrm{\&alpha;}}_i\right)=m\\ f_2\left(\mathrm{\&alpha;}\right)=\frac{U_{\mathrm{sm}\left(5\right)}}{U_d/2}=\frac{4}{5\mathrm{\&pi;}}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{(-1)}^{i+1}\cos \left({5\mathrm{\&alpha;}}_i\right)=0\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ f_N\left(\mathrm{\&alpha;}\right)=\frac{U_{\mathrm{sm}\left(M\right)}}{U_d/2}=\frac{4}{\mathrm{M\&pi;}}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{(-1)}^{i+1}\cos \left({\mathrm{M\&alpha;}}_i\right)=0\end{array}\right.---\left(5\right)$

Obviously, formula (5) is a Nonlinear and transcendental equations.

2. three level neutral-point-clamped photovoltaic DC-to-AC converter mid point electric current Mathematical Modeling is set up:

At a sampling period T _sinterior current in middle wire can be expressed as formula (6):

$\begin{array}{c}{i}_{\mathrm{NP}}=i_{\mathrm{NP}\_\mathrm{Medium}}+i_{\mathrm{NP}\_\mathrm{Small}}\\ =T_M*\left[\begin{array}{ccc}{M}_a& M_b& M_c\end{array}\right]\&CenterDot;\left[\begin{array}{c}{i}_a\\ i_b\\ i_c\end{array}\right]+\left[\begin{array}{cc}{k}_0& k_1\end{array}\right]\&CenterDot;\left[\begin{array}{cc}{T}_{S0}& 0\\ 0& T_{S1}\end{array}\right]\left[\begin{array}{ccc}{S0}_a& {S0}_b& {S0}_c\\ {S1}_a& {S1}_b& {S1}_c\end{array}\right]\left[\begin{array}{c}{i}_a\\ i_b\\ i_c\end{array}\right]\end{array}---\left(6\right)$

In formula: the switch function M that middle vector is corresponding _am _bm _cdefine as shown in table 1:

Vector switch function table in table 1

Middle vector	M a	M b	M c
				pon	0	1	0
opn	1	0	0
				npo	0	0	1
nop	0	1	0
				onp	1	0	0
pno	0	0	1

The switch function S0 that small vector is corresponding _as0 _bs0 _cand S1 _as1 _bs1 _cdefine as shown in table 2.

Table 2 small vector switch function table

Small vector	S0 a	S0 b	S0 c	Small vector	S1 a	S1 b	S1 c
								poo/onn	1	0	0	ppo/oon	0	0	1
opo/non	0	1	0	opp/noo	1	0	0
								pop/nno	0	0	1	pop/ono	0	1	0

Work as i _nP=0 or i _nPwhen → 0, the mid-point voltage of three level neutral-point-clamped photovoltaic DC-to-AC converter reaches balance.

3. continuous space ant colony optimization for solving is adopted:

Ant group algorithm (Ant Colony Algorithm) is that Italian scholar Dorigo M proposed first in 1991 according to the research to Food Recruiment In Ants behavior under nature.It is a complicated intelligent system in essence, has stronger robustness, excellent Distributed Calculation mechanism, is easy to and the feature such as additive method is combined.The TACO (touring ant colony optimization) proposed by people such as Hiroyasu for 2000 with the immediate a kind of continuous space ant group algorithm of Basic Ant Group of Algorithm.Practice shows, use the Filled function ant group algorithm being similar to discrete optimization ant group algorithm structure can try to achieve the optimal solution of function with speed faster, and existing theory can be used very easily in a lot of aspect such as the convergence of this type method, convergence rate.The particular harmonic that continuous space ant group algorithm is applied to the three level neutral-point-clamped photovoltaic DC-to-AC converter considering neutral point voltage balance by the present invention eliminates solving of model, ask for the switch angle that particular harmonic is eliminated, ant group algorithm when solving Nonlinear System of Equations unlike traditional Newton iteration method, its variation tendency not needing the initial value of solving equation and prediction to separate, therefore accelerates computational speed.

Following equation (7) can be obtained by (5) formula and (6) formula: $\left\{\begin{array}{c}{g}_1\left(\mathrm{\&alpha;}\right)=4/\mathrm{\&pi;}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{(-1)}^{i+1}\cos \left({\mathrm{\&alpha;}}_i\right)-m=0\\ g_2\left(\mathrm{\&alpha;}\right)=4/5\mathrm{\&pi;}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{(-1)}^{i+1}\cos \left({5\mathrm{\&alpha;}}_i\right)=0\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ g_{n-1}\left(\mathrm{\&alpha;}\right)=4/\mathrm{N\&pi;}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{(-1)}^{i+1}\cos \left({\mathrm{N\&alpha;}}_i\right)=0\\ g_n\left(\mathrm{\&alpha;}\right)=i_{\mathrm{NP}}=0\end{array}\right.---\left(7\right)$

This equation group can be interpreted as the optimization problem asking n target, that is:

$\mathrm{Min}:\left\{\begin{array}{c}{y}_1={\left(g_1\left(\mathrm{\&alpha;}\right)\right)}^2\\ y_2={\left(g_2\left(\mathrm{\&alpha;}\right)\right)}^2\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ y_{n-1}={\left(g_N\left(\mathrm{\&alpha;}\right)\right)}^2\\ y_n={\left(i_{\mathrm{NP}}\right)}^2\end{array}\right.---\left(8\right)$

According to Objective Programming relative theory, be a target by above n target unification, that is:

$\mathrm{Min}:y=-\frac{1}{1+{y_1}^2+{y_2}^2+...{y_n}^2}---\left(9\right)$

From formula (9): meeting under certain error condition, when n target function all get or close to minimum value 0 time, y also just can reach minimum.In this, as fitness function, utilize TACO just can obtain the approximate solution (collection) of equation, obtain mid point electric current particular harmonic and eliminate control angle.

With cancellation 5,7,11 subharmonic are example, utilize continuous space ant group algorithm to solve an equation and calculate α ₁, α ₂, α ₃, α ₄under the prerequisite ensureing neutral point voltage balance, the solution locus of the switch angle obtained as shown in Figure 1, as modulation degree m=0.8, output line voltage waveform, DC capacitor voltage waveform and line voltage spectrum are as shown in Figure 2, visible while the specific low-order harmonic of elimination, mid-point voltage is well balanced.

Above-described specific embodiment; object of the present invention, technical scheme and beneficial effect are further described; be understood that; the foregoing is only specific embodiments of the invention; be not limited to the present invention; within the spirit and principles in the present invention all, any amendment made, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (2)

1. three level neutral-point-clamped photovoltaic DC-to-AC converter particular harmonic eliminates a control method, it is characterized in that comprising the following steps:

1. set up three level neutral-point-clamped photovoltaic DC-to-AC converter particular harmonic and eliminate control method Mathematical Modeling, solve following Nonlinear and transcendental equations:

If fundamental modulation degree eliminate 5,7,11 ..., 6i-1,6i+1 ... M subharmonic (M be eliminable most high order harmonic component number of times)

$\left\{\begin{array}{c}{f}_1\left(\mathrm{\&alpha;}\right)=\frac{U_{\mathrm{sm}\left(1\right)}}{U_d/2}=\frac{4}{\mathrm{\&pi;}}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{(-1)}^{i+1}\cos \left({\mathrm{\&alpha;}}_i\right)=m\\ f_2\left(\mathrm{\&alpha;}\right)=\frac{U_{\mathrm{sm}\left(5\right)}}{U_d/2}\frac{4}{5\mathrm{\&pi;}}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{(-1)}^{i+1}\cos \left({5\mathrm{\&alpha;}}_i\right)=0\\ .\\ .\\ .\\ f_N\left(\mathrm{\&alpha;}\right)=\frac{U_{\mathrm{sm}\left(M\right)}}{U_d/2}=\frac{4}{\mathrm{M\&pi;}}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{(-1)}^{i+1}\cos \left(M{\mathrm{\&alpha;}}_i\right)=0\end{array}\right.;$

U in formula _dfor DC side supply voltage, N is closed half-convergency number by taking away in 1/4 cycle, and switching angle should satisfy condition: $D:0<{\mathrm{\&alpha;}}_1<{\mathrm{\&alpha;}}_2<...<{\mathrm{\&alpha;}}_{n-1}<{\mathrm{\&alpha;}}_N<\frac{\mathrm{\&pi;}}{2};$

2. three level neutral-point-clamped photovoltaic DC-to-AC converter mid point electric current Mathematical Modeling is set up: at a sampling period T _sinterior current in middle wire can be expressed as:

$\begin{array}{c}{i}_{\mathrm{NP}}=i_{\mathrm{NP}\_\mathrm{Medium}}+i_{\mathrm{NP}\_\mathrm{Small}}\\ =T_M\&CenterDot;\left[\begin{array}{ccc}{M}_a& M_b& M_c\end{array}\right]\&CenterDot;\left[\begin{array}{c}{i}_a\\ i_b\\ i_c\end{array}\right]+\left[\begin{array}{cc}{k}_0& k_1\end{array}\right]\&CenterDot;\left[\begin{array}{cc}{T}_{S0}& 0\\ 0& T_{S1}\end{array}\right]\&CenterDot;\left[\begin{array}{ccc}{S0}_a& {S0}_b& {S0}_c\\ {S1}_a& {S1}_b& {S1}_c\end{array}\right]\left[\begin{array}{c}{i}_a\\ i_b\\ i_c\end{array}\right]\end{array}$

; Work as i _nP=0 or i _nPwhen → 0, the mid-point voltage of three level neutral-point-clamped photovoltaic DC-to-AC converter reaches balance;

3. continuous space ant colony optimization for solving is adopted:

1. 2. following equation can be obtained with step by step: $\left\{\begin{array}{c}{g}_1\left(\mathrm{\&alpha;}\right)=4/\mathrm{\&pi;}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{(-1)}^{i+1}\cos \left({\mathrm{\&alpha;}}_i\right)-m=0\\ g_2\left(\mathrm{\&alpha;}\right)=4/5\mathrm{\&pi;}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{(-1)}^{i+1}\cos \left({5\mathrm{\&alpha;}}_i\right)=0\\ .\\ .\\ .\\ g_{n-1}\left(\mathrm{\&alpha;}\right)=4/\mathrm{N\&pi;}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{(-1)}^{i+1}\cos \left({\mathrm{N\&alpha;}}_i\right)=0\\ g_n\left(\mathrm{\&alpha;}\right)=i_{\mathrm{NP}}=0\end{array}\right.$

This equation group is interpreted as the optimization problem asking n target, that is:

$\mathrm{Min}:\left\{\begin{array}{c}{y}_1={\left(g_1\left(\mathrm{\&alpha;}\right)\right)}^2\\ y_2={\left(g_2\left(\mathrm{\&alpha;}\right)\right)}^2\\ .\\ .\\ .\\ y_{n-1}={\left(g_N\left(\mathrm{\&alpha;}\right)\right)}^2\\ y_n={\left(i_{\mathrm{NP}}\right)}^2\end{array}\right.$

According to Objective Programming principle, be a target by above n target unification, that is:

$\mathrm{Min}:y=-\frac{1}{1+{y_1}^2+{y_2}^2+...+{y_n}^2}.$

2. three level neutral-point-clamped photovoltaic DC-to-AC converter particular harmonic according to claim 1 eliminates control method, it is characterized in that:

Step 2. in, the switch function M that middle vector is corresponding _am _bm _cbe defined as:

Middle vector M _a M _b M _c pon 0 1 0 opn 1 0 0 npo 0 0 1 nop 0 1 0 onp 1 0 0 pno 0 0 1

The switch function S0 that small vector is corresponding _as0 _bs0 _cand S1 _as1 _bs1 _cbe defined as:

Small vector S0 _a S0 _b S0 _c Small vector S1 _a S1 _b S1 _c

poo/onn 1 0 0 ppo/oon 0 0 1 opo/non 0 1 0 opp/noo 1 0 0 pop/nno 0 0 1 pop/ono 0 1 0

。