CN102082522A - Voltage step controlling method and step wave cascade multilevel inverter - Google Patents

Abstract

The present invention discloses a voltage step controlling method and a step wave cascade multilevel inverter, wherein the voltage step controlling method comprises the steps of: obtaining an output voltage of a photovoltaic cell; calculating voltage steps of the output voltage by using a step wave superposition method to obtain the voltages of n voltage steps, wherein the voltages of the n voltage steps are respectively represented by from u1 to un; normalizing the voltages of the n voltage steps to obtain results represented by from k1 to kn; calculating the conduction angles of the n voltage steps, wherein the conduction angles represented by from theta 1 to theta n respectively corresponds to from the 1st to the n-th voltage step; and respectively controlling the conduction of the 1st to the nth voltage steps by using the conduction angles represented by from theta 1 to theta n to convert a DC multilevel input into an AC level output. The conduction angles of the invention are calculated by normalizing the voltage steps and the voltage step differences can be different from each other. The technical scheme of the invention has an advantage of high inversion controlling precision and enables a photovoltaic cell outputting voltage with any amplitude cascaded.

Description

Voltage step control method and staircase waveform cascaded multilevel inverter

Technical field

The present invention relates to staircase waveform cascade connection multi-level inversion transformation technique field, relate in particular to a kind of voltage step control method and staircase waveform cascaded multilevel inverter.

Background technology

H bridge cascaded multilevel inverter has the plurality of advantages of multi-electrical level inverter, is widely used in occasions such as motor-driven, high-power active power filterings, is one of important development direction of large power, electrically force transducer.Because the cascade multi-level inversion needs a plurality of independent DC power supplies, it is particularly suitable as the inverter of solar photovoltaic generating system.The staircase waveform stacked system is a cascaded multilevel inverter groundwork pattern, and this mode of operation biggest advantage is: switching device operating frequency low (fundamental frequency), efficient height, electromagnetic interference (EMI) are little.

Existing cascaded multilevel inverter operation principle is as follows, and calculating voltage step at first, the voltage step difference between the voltage step equate, derive the angle of flow of each voltage step then, realizes that by the control angle of flow direct current delivers stream.Because the influence of discrete type, climate temperature and the installation site of the voltage-current characteristic of equipment can cause the voltage step difference of stack inequality, the inversion control error of prior art is bigger; In order to guarantee that the voltage step difference equates, need to limit the output voltage amplitude of the photovoltaic cell of cascade, the photovoltaic cell that prior art can not any output voltage amplitude of cascade.

Summary of the invention

The invention provides a kind of voltage step control method and staircase waveform cascaded multilevel inverter, its inversion control precision height, but and the photovoltaic cell of any output voltage amplitude of cascade.

The voltage step control method of the staircase waveform cascaded multilevel inverter that different voltages are differential comprises:

A. obtain the output voltage of photovoltaic cell, utilize the voltage step of staircase waveform stacking method calculating output voltage, obtain the voltage of n voltage step, wherein, n voltage step is respectively the 1st, 2 ..., i, ..., n voltage step, the voltage of n voltage step is respectively u ₁, u ₂..., u _i..., u _n

B. to the voltage u of n voltage step ₁, u ₂..., u _i..., u _nCarry out normalized, obtain k ₁, k ₂..., k _i..., k _n, wherein, k _n=1;

C. calculate the 1st, 2 ..., i ..., the conduction angle of n-1 voltage step ₁, θ ₂..., θ _i..., θ _N-1:

$\left\{\begin{array}{c}{\mathrm{\θ}}_1=\frac{{\sin }^{-1}\left(k_1\right)}{2}\\ {\mathrm{\θ}}_2=\frac{{\sin }^{-1}\left(k_2\right)+{\sin }^{-1}\left(k_3\right)}{2}\\ ......\\ {\mathrm{\θ}}_i=\frac{{\sin }^{-1}\left(k_i\right)+{\sin }^{-1}\left(k_{i+1}\right)}{2}\\ ......\\ {\mathrm{\θ}}_{n-1}=\frac{{\sin }^{-1}\left(k_{n-1}\right)+{\sin }^{-1}\left(k_n\right)}{2}\end{array}\right.$

D. calculate the conduction angle of n voltage step _n:

-k ₁θ ₁+(k ₁-k ₂)θ ₂+…+(k _N-1-k _N)θ _N+90°＝180°/π

Wherein, the constraints of the angle of flow is:

$\left\{\begin{array}{c}0<{\mathrm{\&theta;}}_1<{\sin }^{-1}{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ {\sin }^{-1}{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1<{\mathrm{\&theta;}}_2<{\sin }^{-1}{k}_2\\ {\sin }^{-1}{k}_2<{\mathrm{\&theta;}}_3<{\sin }^{-1}{k}_3\\ ...\\ {\sin }^{-1}{k}_{i-1}<{\mathrm{\&theta;}}_i<{\sin }^{-1}{k}_i\\ ...\\ {\sin }^{-1}{k}_{n-1}<{\mathrm{\&theta;}}_n<{\sin }^{-1}{k}_n=\frac{\mathrm{\&pi;}}{2}\end{array}\right.$

E. utilize the conduction angle that calculates ₁, θ ₂..., θ _i..., θ _N-1, θ _n, control the 1st, 2 respectively ..., i ..., n-1, the conducting of n voltage step is with the output of the many level inputs becoming of direct current interchange level.

Preferably, steps A specifically comprises: obtain the output voltage of j group photovoltaic cell, obtain j output voltage; Utilize the voltage step of j output voltage of staircase waveform stacking method calculating, obtain the voltage of n voltage step, wherein, n voltage step is respectively the 1st, 2 ..., i ..., n voltage step, the voltage of n voltage step is respectively u ₁, u ₂..., u _i..., u _nWherein, the quantity n of voltage step is:

For j output voltage carried out permutation and combination, n ₀Quantity for voltage step stack back equivalent voltage.

Preferably, after the step D, further comprise step F: calculate plateau voltage normalization difference DELTA u ₁, Δ u ₂..., Δ u _i..., Δ u _n:

$\left\{\begin{array}{c}{\mathrm{\&Delta;u}}_1={\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ {\mathrm{\&Delta;u}}_2=k_2-{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ ...\\ {\mathrm{\&Delta;u}}_i=k_i-k_{i-1}\\ ...\\ {\mathrm{\&Delta;u}}_n=k_{n-1}-k_n\end{array}\right.$

The general formula of output voltage is:

$u_m=u_n\underset{m=\mathrm{1,3,5}...}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\frac{4}{\mathrm{m\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{m\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{m\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{m\&theta;}}_n]\sin m\left(\mathrm{\&omega;t}\right)$

Wherein, m=1,3,5 ...., ∞;

M gets 1 in the general formula, calculates the fundamental voltage value of output voltage:

$u_1=u_{\mathrm{<figure-callout\; id="4"\; label="n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">n</figure-callout>}}\frac{4}{\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{\&theta;}}_n]\sin \left(\mathrm{\&omega;t}\right)$

Judge whether the fundamental voltage value that calculates belongs in the benchmark fundamental voltage value scope that presets, if, the output voltage of uncomfortable lay the grain volt battery, otherwise, the output voltage of adjustment photovoltaic cell.

Preferably, after the step D, further comprise step F:

Calculate plateau voltage normalization difference DELTA u ₁, Δ u ₂..., Δ u _i..., Δ u _n:

$\left\{\begin{array}{c}{\mathrm{\&Delta;u}}_1={\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ {\mathrm{\&Delta;u}}_2=k_2-{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ ...\\ {\mathrm{\&Delta;u}}_i=k_i-k_{i-1}\\ ...\\ {\mathrm{\&Delta;u}}_n=k_{n-1}-k_n\end{array}\right.$

The general formula of output voltage is:

$u_m=u_n\underset{m=\mathrm{1,3,5}...}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\frac{4}{\mathrm{m\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{m\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{m\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{m\&theta;}}_n]\sin m\left(\mathrm{\&omega;t}\right)$

Wherein, m=1,3,5 ...., ∞;

M gets 1 in the general formula, calculates the fundamental voltage value of output voltage:

$u_1=u_{\mathrm{<figure-callout\; id="4"\; label="n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">n</figure-callout>}}\frac{4}{\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{\&theta;}}_n]\sin \left(\mathrm{\&omega;t}\right)$

M gets 3,5,7 in the general formula ..., p; Calculate the 3rd, 5,7 of output voltage ..., p subharmonic voltage value, they are respectively u ₃, u ₅, u ₇..., u _p:

$\left\{\begin{array}{c}{u}_3=u_{\mathrm{<figure-callout\; id="4"\; label="n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">n</figure-callout>}}\frac{4}{3\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 3\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 3\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 3\mathrm{\&theta;}}_n]\sin \left(3\mathrm{\&omega;t}\right)\\ u_5=u_{\mathrm{<figure-callout\; id="4"\; label="n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">n</figure-callout>}}\frac{4}{5\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\mathrm{<figure-callout\; id="5"\; label="cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">cos</figure-callout>}5\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\mathrm{<figure-callout\; id="5"\; label="cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">cos</figure-callout>}5\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_{\mathrm{<figure-callout\; id="5"\; label="n\; cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">n</figure-callout>}}{\cos }_{}{5\mathrm{\&theta;}}_n]\sin \left(5\mathrm{\&omega;t}\right)\\ u_7=u_{\mathrm{<figure-callout\; id="4"\; label="n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">n</figure-callout>}}\frac{4}{7\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 7\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 7\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 7\mathrm{\&theta;}}_n]\sin \left(7\mathrm{\&omega;t}\right)\\ ...\\ u_p=u_{\mathrm{<figure-callout\; id="4"\; label="n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">n</figure-callout>}}\frac{4}{\mathrm{p\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{p\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{p\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{p\&theta;}}_n]\sin \left(\mathrm{p\&omega;t}\right)\end{array}\right.$

Calculate the 3rd time to the p time voltage total harmonic distortion:

$\mathrm{THD}=\frac{\sqrt{\underset{m=\mathrm{3,5,7}...}{\overset{p}{\mathrm{\&Sigma;}}}{u}_m^2}}{u_1}$

Wherein, m=3,5,7 ..., p;

Whether judge the voltage total harmonic distortion that calculates less than the reference voltage total harmonic distortion that presets, if, the output voltage of uncomfortable lay the grain volt battery, otherwise, the output voltage of adjustment photovoltaic cell.

Preferably, after the step D, further comprise step F:

Calculate plateau voltage normalization difference DELTA u ₁, Δ u ₂..., Δ u _i..., Δ u _n:

$\left\{\begin{array}{c}{\mathrm{\&Delta;u}}_1={\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ {\mathrm{\&Delta;u}}_2=k_2-{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ ...\\ {\mathrm{\&Delta;u}}_i=k_i-k_{i-1}\\ ...\\ {\mathrm{\&Delta;u}}_n=k_{n-1}-k_n\end{array}\right.$

The general formula of output voltage is:

$u_m=u_n\underset{m=\mathrm{1,3,5}...}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\frac{4}{\mathrm{m\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{m\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{m\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{m\&theta;}}_n]\sin m\left(\mathrm{\&omega;t}\right)$

Wherein, m=1,3,5 ...., ∞;

M gets 1 in the general formula, calculates the fundamental voltage value of output voltage:

$u_1=u_{\mathrm{<figure-callout\; id="4"\; label="n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">n</figure-callout>}}\frac{4}{\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{\&theta;}}_n]\sin \left(\mathrm{\&omega;t}\right)$

M gets 3,5,7 in the general formula ..., p; Calculate the 3rd, 5,7 of output voltage ..., p subharmonic voltage value, they are respectively u ₃, u ₅, u ₇..., u _p:

$\left\{\begin{array}{c}{u}_3=u_{\mathrm{<figure-callout\; id="4"\; label="n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">n</figure-callout>}}\frac{4}{3\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 3\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 3\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 3\mathrm{\&theta;}}_n]\sin \left(3\mathrm{\&omega;t}\right)\\ u_5=u_{\mathrm{<figure-callout\; id="4"\; label="n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">n</figure-callout>}}\frac{4}{5\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\mathrm{<figure-callout\; id="5"\; label="cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">cos</figure-callout>}5\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\mathrm{<figure-callout\; id="5"\; label="cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">cos</figure-callout>}5\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_{\mathrm{<figure-callout\; id="5"\; label="n\; cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">n</figure-callout>}}{\cos }_{}{5\mathrm{\&theta;}}_n]\sin \left(5\mathrm{\&omega;t}\right)\\ u_7=u_{\mathrm{<figure-callout\; id="4"\; label="n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">n</figure-callout>}}\frac{4}{7\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 7\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 7\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 7\mathrm{\&theta;}}_n]\sin \left(7\mathrm{\&omega;t}\right)\\ ...\\ u_p=u_{\mathrm{<figure-callout\; id="4"\; label="n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">n</figure-callout>}}\frac{4}{\mathrm{p\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{p\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{p\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{p\&theta;}}_n]\sin \left(\mathrm{p\&omega;t}\right)\end{array}\right.$

Calculate the 3rd time to the p time voltage total harmonic distortion:

$\mathrm{THD}=\frac{\sqrt{\underset{m=\mathrm{3,5,7}...}{\overset{p}{\mathrm{\&Sigma;}}}{u}_m^2}}{u_1}$

Wherein, m=3,5,7 ..., p;

If the fundamental voltage value that calculates belongs in the benchmark fundamental voltage value scope that presets, and the voltage total harmonic distortion that calculates is less than the reference voltage total harmonic distortion that presets, the output voltage of then uncomfortable lay the grain volt battery; Otherwise, the output voltage of adjustment photovoltaic cell.

A kind of staircase waveform cascaded multilevel inverter comprises:

Voltage step acquiring unit is used to obtain the output voltage of photovoltaic cell, utilizes the staircase waveform stacking method to calculate the voltage step of output voltage, obtains the voltage of n voltage step; Wherein, n voltage step is respectively the 1st, 2 ..., i ..., n voltage step, the voltage of n voltage step is respectively u ₁, u ₂..., u _i..., u _n

Voltage step normalization unit is used for the voltage u to n voltage step ₁, u ₂..., u _i..., u _nCarry out normalized, obtain k ₁, k ₂..., k _i..., k _n, wherein, k _n=1;

Angle of flow computing unit is used to calculate the 1st, 2 ..., i ..., the conduction angle of n-1 voltage step ₁, θ ₂..., θ _i..., θ _N-1:

$\left\{\begin{array}{c}{\mathrm{\&theta;}}_1=\frac{{\sin }^{-1}\left(k_1\right)}{2}\\ {\mathrm{\&theta;}}_2=\frac{{\sin }^{-1}\left(k_2\right)+{\sin }^{-1}\left(k_3\right)}{2}\\ ......\\ {\mathrm{\&theta;}}_i=\frac{{\sin }^{-1}\left(k_i\right)+{\sin }^{-1}\left(k_{i+1}\right)}{2}\\ ......\\ {\mathrm{\&theta;}}_{n-1}=\frac{{\sin }^{-1}\left(k_{n-1}\right)+{\sin }^{-1}\left(k_n\right)}{2}\end{array}\right.$

Calculate the conduction angle of n voltage step _n:

-k ₁θ ₁+(k ₁-k ₂)θ ₂+…+(k _N-1-k _N)θ _N+90°＝180°/π

Wherein, the constraints of the angle of flow is:

$\left\{\begin{array}{c}0<{\mathrm{\&theta;}}_1<{\sin }^{-1}{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ {\sin }^{-1}{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1<{\mathrm{\&theta;}}_2<{\sin }^{-1}{k}_2\\ {\sin }^{-1}{k}_2<{\mathrm{\&theta;}}_3<{\sin }^{-1}{k}_3\\ ...\\ {\sin }^{-1}{k}_{i-1}<{\mathrm{\&theta;}}_i<{\sin }^{-1}{k}_i\\ ...\\ {\sin }^{-1}{k}_{n-1}<{\mathrm{\&theta;}}_n<{\sin }^{-1}{k}_n=\frac{\mathrm{\&pi;}}{2}\end{array}\right.$

Voltage step conducting control unit is used to utilize the conduction angle that calculates ₁, θ ₂..., θ _i..., θ _N-1, θ _n, control the 1st, 2 respectively ..., i ..., n-1, the conducting of n voltage step is with the output of the many level inputs becoming of direct current interchange level.

Preferably, voltage step acquiring unit comprises:

The output voltage acquiring unit is used to obtain the output voltage that j organizes photovoltaic cell, obtains j output voltage;

Voltage step computing unit is used to utilize the staircase waveform stacking method to calculate the voltage step of j output voltage, obtains the voltage of n voltage step, wherein, n voltage step is respectively the 1st, 2 ..., i, ..., n voltage step, the voltage of n voltage step is respectively u ₁, u ₂..., u _i..., u _n

Wherein, the quantity n of voltage step is:

For j output voltage carried out permutation and combination, n ₀Quantity for voltage step stack back equivalent voltage.

Preferably, further comprise the output voltage adjustment unit;

The output voltage adjustment unit is used to calculate plateau voltage normalization difference DELTA u ₁, Δ u ₂..., Δ u _i..., Δ u _n:

$\left\{\begin{array}{c}{\mathrm{\&Delta;<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1={\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ {\mathrm{\&Delta;u}}_2=k_2-{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ ...\\ {\mathrm{\&Delta;u}}_i=k_i-k_{i-1}\\ ...\\ {\mathrm{\&Delta;u}}_n=k_{n-1}-k_n\end{array}\right.$

The general formula of output voltage is:

$u_m=u_n\underset{m=\mathrm{1,3,5}...}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\frac{4}{\mathrm{m\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{m\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{m\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{m\&theta;}}_n]\sin m\left(\mathrm{\&omega;t}\right)$

Wherein, m=1,3,5 ...., ∞;

M gets 1 in the general formula, calculates the fundamental voltage value of output voltage:

${\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{\&theta;}}_n]\sin \left(\mathrm{\&omega;t}\right)$

Judge whether the fundamental voltage value that calculates belongs in the benchmark fundamental voltage value scope that presets, if, the output voltage of uncomfortable lay the grain volt battery, otherwise, the output voltage of adjustment photovoltaic cell.

Preferably, further comprise the output voltage adjustment unit;

The output voltage adjustment unit is used to calculate plateau voltage normalization difference DELTA u ₁, Δ u ₂..., Δ u _i..., Δ u _n:

$\left\{\begin{array}{c}{\mathrm{\&Delta;<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1={\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ {\mathrm{\&Delta;u}}_2=k_2-{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ ...\\ {\mathrm{\&Delta;u}}_i=k_i-k_{i-1}\\ ...\\ {\mathrm{\&Delta;u}}_n=k_{n-1}-k_n\end{array}\right.$

The general formula of output voltage is:

$u_m=u_n\underset{m=\mathrm{1,3,5}...}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\frac{4}{\mathrm{m\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{m\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{m\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{m\&theta;}}_n]\sin m\left(\mathrm{\&omega;t}\right)$

Wherein, m=1,3,5 ...., ∞;

M gets 1 in the general formula, calculates the fundamental voltage value of output voltage:

${\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{\&theta;}}_n]\sin \left(\mathrm{\&omega;t}\right)$

M gets 3,5,7 in the general formula ..., p; Calculate the 3rd, 5,7 of output voltage ..., p subharmonic voltage value, they are respectively u ₃, u ₅, u ₇..., u _p:

$\left\{\begin{array}{c}{u}_3={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{3\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 3\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 3\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 3\mathrm{\&theta;}}_n]\sin \left(3\mathrm{\&omega;t}\right)\\ {\mathrm{<figure-callout\; id="5"\; label="u"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">u</figure-callout>}}_5={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{5\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\mathrm{<figure-callout\; id="5"\; label="cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">cos</figure-callout>}5\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\mathrm{<figure-callout\; id="5"\; label="cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">cos</figure-callout>}5\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_{\mathrm{<figure-callout\; id="5"\; label="n\; cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">n</figure-callout>}}{\cos }_{}{5\mathrm{\&theta;}}_n]\sin \left(5\mathrm{\&omega;t}\right)\\ u_7={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{7\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 7\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 7\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 7\mathrm{\&theta;}}_n]\sin \left(7\mathrm{\&omega;t}\right)\\ ...\\ u_p={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{\mathrm{p\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{p\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{p\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{p\&theta;}}_n]\sin \left(\mathrm{p\&omega;t}\right)\end{array}\right.$

Calculate the 3rd time to the p time voltage total harmonic distortion:

$\mathrm{THD}=\frac{\sqrt{\underset{m=\mathrm{3,5,7}...}{\overset{p}{\mathrm{\&Sigma;}}}{u}_m^2}}{{\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1}$

Wherein, m=3,5,7 ..., p;

Whether judge the voltage total harmonic distortion that calculates less than the reference voltage total harmonic distortion that presets, if, the output voltage of uncomfortable lay the grain volt battery, otherwise, the output voltage of adjustment photovoltaic cell.

Preferably, further comprise the output voltage adjustment unit;

The output voltage adjustment unit is used to calculate plateau voltage normalization difference DELTA u ₁, Δ u ₂..., Δ u _i..., Δ u _n:

$\left\{\begin{array}{c}{\mathrm{\&Delta;<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1={\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ {\mathrm{\&Delta;u}}_2=k_2-{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ ...\\ {\mathrm{\&Delta;u}}_i=k_i-k_{i-1}\\ ...\\ {\mathrm{\&Delta;u}}_n=k_{n-1}-k_n\end{array}\right.$

The general formula of output voltage is:

$u_m=u_n\underset{m=\mathrm{1,3,5}...}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\frac{4}{\mathrm{m\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{m\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{m\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{m\&theta;}}_n]\sin m\left(\mathrm{\&omega;t}\right)$

Wherein, m=1,3,5 ...., ∞;

M gets 1 in the general formula, calculates the fundamental voltage value of output voltage:

${\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{\&theta;}}_n]\sin \left(\mathrm{\&omega;t}\right)$

M gets 3,5,7 in the general formula ..., p; Calculate the 3rd, 5,7 of output voltage ..., p subharmonic voltage value, they are respectively u ₃, u ₅, u ₇..., u _p:

$\left\{\begin{array}{c}{u}_3={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{3\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 3\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 3\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 3\mathrm{\&theta;}}_n]\sin \left(3\mathrm{\&omega;t}\right)\\ {\mathrm{<figure-callout\; id="5"\; label="u"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">u</figure-callout>}}_5={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{5\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\mathrm{<figure-callout\; id="5"\; label="cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">cos</figure-callout>}5\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\mathrm{<figure-callout\; id="5"\; label="cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">cos</figure-callout>}5\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_{\mathrm{<figure-callout\; id="5"\; label="n\; cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">n</figure-callout>}}{\cos }_{}{5\mathrm{\&theta;}}_n]\sin \left(5\mathrm{\&omega;t}\right)\\ u_7={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{7\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 7\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 7\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 7\mathrm{\&theta;}}_n]\sin \left(7\mathrm{\&omega;t}\right)\\ ...\\ u_p={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{\mathrm{p\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{p\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{p\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{p\&theta;}}_n]\sin \left(\mathrm{p\&omega;t}\right)\end{array}\right.$

Calculate the 3rd time to the p time voltage total harmonic distortion:

$\mathrm{THD}=\frac{\sqrt{\underset{m=\mathrm{3,5,7}...}{\overset{p}{\mathrm{\&Sigma;}}}{u}_m^2}}{{\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1}$

Wherein, m=3,5,7 ..., p;

If the fundamental voltage value that calculates belongs in the benchmark fundamental voltage value scope that presets, and the voltage total harmonic distortion that calculates is less than the reference voltage total harmonic distortion that presets, the output voltage of then uncomfortable lay the grain volt battery; Otherwise, the output voltage of adjustment photovoltaic cell.

Beneficial effect of the present invention: among the present invention, obtain the output voltage of photovoltaic cell, utilize the voltage step of staircase waveform stacking method calculating output voltage, obtain the voltage of n voltage step, wherein, n voltage step is respectively the 1st, 2 ... i,, n voltage step, the voltage of n voltage step is respectively u ₁, u ₂..., u _i..., u _nVoltage u to n voltage step ₁, u ₂..., u _i..., u _nCarry out normalized, obtain k ₁, k ₂..., k _i..., k _n, wherein, k _n=1; Calculate the 1st, 2 ..., i ..., the conduction angle of n-1 voltage step ₁, θ ₂..., θ _i..., θ _N-1Calculate the conduction angle of n voltage step _nUtilize θ ₁, θ ₂..., θ _i..., θ _N-1, θ _n, control the 1st, 2 respectively ..., i ..., n-1, the conducting of n voltage step is with the output of the many level inputs becoming of direct current interchange level.The angle of flow of the present invention is calculated by the normalization of voltage step, and the voltage step difference can be inequality, need not to limit the output voltage amplitude of the photovoltaic cell of cascade, the technical program inversion control precision height, but and the photovoltaic cell of any output voltage amplitude of cascade.

Description of drawings

Fig. 1 is the method flow diagram of the embodiment of the invention one;

Fig. 2 is the cascaded multilevel inverter schematic diagram of the embodiment of the invention one;

Fig. 3 is the normalization value schematic diagram of the embodiment of the invention one;

Fig. 4 is the synthetic schematic diagram of the output voltage of the embodiment of the invention one;

Fig. 5 is the cascaded multilevel inverter schematic diagram of three groups of voltage cascades of the embodiment of the invention two;

Fig. 6 is the output voltage of the embodiment of the invention two and the analogous diagram of load current waveform;

Fig. 7 is the spectrogram of the output voltage of the embodiment of the invention two;

Fig. 8 is the spectrogram of the load current of the embodiment of the invention two.

Embodiment

Embodiment one

Referring to Fig. 1 to Fig. 4, the present invention is described in detail below in conjunction with accompanying drawing.

The voltage step control method of the staircase waveform cascaded multilevel inverter that different voltages are differential comprises:

Step 101. is obtained the output voltage of photovoltaic cell, utilizes the voltage step of staircase waveform stacking method calculating output voltage, obtains the voltage of n voltage step, wherein, n voltage step is respectively the 1st, 2 .., i, ..., n voltage step, the voltage of n voltage step is respectively u ₁, u ₂..., u _i..., u _n

The voltage u of step 102. a couple n voltage step ₁, u ₂..., u _i..., u _nCarry out normalized, obtain k ₁, k ₂..., k _i..., k _n, wherein, k _n=1;

Step 103. calculates the 1st, 2 ..., i ..., the conduction angle of n-1 voltage step ₁, θ ₂..., θ _i..., θ _N-1, θ ₁～θ ₆Be taken at θ _{I-1, i}With θ _{I, i+1}The centre position:

$\left\{\begin{array}{c}{\mathrm{\&theta;}}_1=\frac{{\sin }^{-1}\left(k_1\right)}{2}\\ {\mathrm{\&theta;}}_2=\frac{{\sin }^{-1}\left(k_2\right)+{\sin }^{-1}\left(k_3\right)}{2}\\ ......\\ {\mathrm{\&theta;}}_i=\frac{{\sin }^{-1}\left(k_i\right)+{\sin }^{-1}\left(k_{i+1}\right)}{2}\\ ......\\ {\mathrm{\&theta;}}_{n-1}=\frac{{\sin }^{-1}\left(k_{n-1}\right)+{\sin }^{-1}\left(k_n\right)}{2}\end{array}\right.$ Formula 1

Calculate the conduction angle of n voltage step _n:

-k ₁θ ₁+ (k ₁-k ₂) θ ₂+ ... + (k _N-1-k _N) θ _N+ 90 °=180 °/π formula 2

Wherein, the constraints of the angle of flow is:

$\left\{\begin{array}{c}0<{\mathrm{\&theta;}}_1<{\sin }^{-1}{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ {\sin }^{-1}{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1<{\mathrm{\&theta;}}_2<{\sin }^{-1}{k}_2\\ {\sin }^{-1}{k}_2<{\mathrm{\&theta;}}_3<{\sin }^{-1}{k}_3\\ ...\\ {\sin }^{-1}{k}_{i-1}<{\mathrm{\&theta;}}_i<{\sin }^{-1}{k}_i\\ ...\\ {\sin }^{-1}{k}_{n-1}<{\mathrm{\&theta;}}_n<{\sin }^{-1}{k}_n=\frac{\mathrm{\&pi;}}{2}\end{array}\right.$ Formula 6

The conduction angle that step 104. utilization calculates ₁, θ ₂..., θ _i..., θ _N-1, θ _n, control the 1st, 2 respectively ..., i ..., n-1, the conducting of n voltage step is with the output of the many level inputs becoming of direct current interchange level.

The angle of flow of the present invention is calculated by the normalization of voltage step, and the voltage step difference can be inequality, need not to limit the output voltage amplitude of the photovoltaic cell of cascade, the technical program inversion control precision height, but and the photovoltaic cell of any output voltage amplitude of cascade.The different voltages of this programme are differential, refer to different voltage step differences.

In the present embodiment, step 101 specifically comprises: obtain the output voltage of j group photovoltaic cell, obtain j output voltage; Utilize the voltage step of j output voltage of staircase waveform stacking method calculating, obtain the voltage of n voltage step, wherein, n voltage step is respectively the 1st, 2 ..., i ..., n voltage step, the voltage of n voltage step is respectively u ₁, u ₂..., u _i..., u _nWherein, the quantity n of voltage step is:

For j output voltage carried out permutation and combination, n ₀Quantity for voltage step stack back equivalent voltage.As another kind of preferred implementation, the quantity n of voltage step is:

This mode need not deduct the quantity of stack back equivalent voltage.The quantity n computational methods of two kinds of above-mentioned voltage steps can be selected according to actual conditions.

In the present embodiment, judge whether to need to adjust the output voltage of photovoltaic cell, following three kinds of preferred implementations are provided by the fundamental voltage value that calculates and/or voltage total harmonic distortion.These three kinds of modes can be selected according to actual environment.

Optimal way one:

Calculate plateau voltage normalization difference DELTA u ₁, Δ u ₂..., Δ u _i..., Δ u _n:

$\left\{\begin{array}{c}{\mathrm{\&Delta;<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1={\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ {\mathrm{\&Delta;u}}_2=k_2-{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ ...\\ {\mathrm{\&Delta;u}}_i=k_i-k_{i-1}\\ ...\\ {\mathrm{\&Delta;u}}_n=k_{n-1}-k_n\end{array}\right.$ Formula 3

The general formula of output voltage is:

$u_m=u_n\underset{m=\mathrm{1,3,5}...}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\frac{4}{\mathrm{m\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{m\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{m\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{m\&theta;}}_n]\sin m\left(\mathrm{\&omega;t}\right)$ Formula 4

Wherein, m=1,3,5 ...., ∞;

M gets 1 in the general formula, calculates the fundamental voltage value of output voltage:

${\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{\&theta;}}_n]\sin \left(\mathrm{\&omega;t}\right)$

Judge whether the fundamental voltage value that calculates belongs in the benchmark fundamental voltage value scope that presets, if, the output voltage of uncomfortable lay the grain volt battery, otherwise, the output voltage of adjustment photovoltaic cell.

Optimal way two:

Calculate plateau voltage normalization difference DELTA u ₁, Δ u ₂..., Δ u _i..., Δ u _n:

$\left\{\begin{array}{c}{\mathrm{\&Delta;<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1={\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ {\mathrm{\&Delta;u}}_2=k_2-{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ ...\\ {\mathrm{\&Delta;u}}_i=k_i-k_{i-1}\\ ...\\ {\mathrm{\&Delta;u}}_n=k_{n-1}-k_n\end{array}\right.$

The general formula of output voltage is:

$u_m=u_n\underset{m=\mathrm{1,3,5}...}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\frac{4}{\mathrm{m\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{m\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{m\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{m\&theta;}}_n]\sin m\left(\mathrm{\&omega;t}\right)$

Wherein, m=1,3,5 ...., ∞;

M gets 1 in the general formula, calculates the fundamental voltage value of output voltage:

${\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{\&theta;}}_n]\sin \left(\mathrm{\&omega;t}\right)$

M gets 3,5,7 in the general formula ..., p; Calculate the 3rd, 5,7 of output voltage ..., p subharmonic voltage value, they are respectively u ₃, u ₅, u ₇..., u _p:

$\left\{\begin{array}{c}{u}_3={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{3\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 3\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 3\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 3\mathrm{\&theta;}}_n]\sin \left(3\mathrm{\&omega;t}\right)\\ {\mathrm{<figure-callout\; id="5"\; label="u"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">u</figure-callout>}}_5={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{5\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\mathrm{<figure-callout\; id="5"\; label="cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">cos</figure-callout>}5\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\mathrm{<figure-callout\; id="5"\; label="cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">cos</figure-callout>}5\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_{\mathrm{<figure-callout\; id="5"\; label="n\; cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">n</figure-callout>}}{\cos }_{}{5\mathrm{\&theta;}}_n]\sin \left(5\mathrm{\&omega;t}\right)\\ u_7={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{7\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 7\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 7\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 7\mathrm{\&theta;}}_n]\sin \left(7\mathrm{\&omega;t}\right)\\ ...\\ u_p={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{\mathrm{p\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{p\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{p\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{p\&theta;}}_n]\sin \left(\mathrm{p\&omega;t}\right)\end{array}\right.$ Formula 7

Calculate the 3rd time to the p time voltage total harmonic distortion:

$\mathrm{THD}=\frac{\sqrt{\underset{m=\mathrm{3,5,7}...}{\overset{p}{\mathrm{\&Sigma;}}}{u}_m^2}}{{\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1}$ Formula 5

Wherein, m=3,5,7 ..., p;

Whether judge the voltage total harmonic distortion that calculates less than the reference voltage total harmonic distortion that presets, if, the output voltage of uncomfortable lay the grain volt battery, otherwise, the output voltage of adjustment photovoltaic cell.

The span of P is unsuitable excessive, and is also unsuitable too small, can require to decide according to reality.

Optimal way three:

Calculate plateau voltage normalization difference DELTA u ₁, Δ u ₂..., Δ u _i..., Δ u _n:

$\left\{\begin{array}{c}{\mathrm{\&Delta;<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1={\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ {\mathrm{\&Delta;u}}_2=k_2-{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ ...\\ {\mathrm{\&Delta;u}}_i=k_i-k_{i-1}\\ ...\\ {\mathrm{\&Delta;u}}_n=k_{n-1}-k_n\end{array}\right.$

The general formula of output voltage is:

$u_m=u_n\underset{m=\mathrm{1,3,5}...}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\frac{4}{\mathrm{m\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{m\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{m\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{m\&theta;}}_n]\sin m\left(\mathrm{\&omega;t}\right)$

Wherein, m=1,3,5 ...., ∞;

M gets 1 in the general formula, calculates the fundamental voltage value of output voltage:

${\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{\&theta;}}_n]\sin \left(\mathrm{\&omega;t}\right)$

M gets 3,5,7 in the general formula ..., p; Calculate the 3rd, 5,7 of output voltage ..., p subharmonic voltage value, they are respectively u ₃, u ₅, u ₇..., u _p:

$\left\{\begin{array}{c}{u}_3={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{3\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 3\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 3\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 3\mathrm{\&theta;}}_n]\sin \left(3\mathrm{\&omega;t}\right)\\ {\mathrm{<figure-callout\; id="5"\; label="u"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">u</figure-callout>}}_5={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{5\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\mathrm{<figure-callout\; id="5"\; label="cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">cos</figure-callout>}5\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\mathrm{<figure-callout\; id="5"\; label="cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">cos</figure-callout>}5\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_{\mathrm{<figure-callout\; id="5"\; label="n\; cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">n</figure-callout>}}{\cos }_{}{5\mathrm{\&theta;}}_n]\sin \left(5\mathrm{\&omega;t}\right)\\ u_7={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{7\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 7\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 7\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 7\mathrm{\&theta;}}_n]\sin \left(7\mathrm{\&omega;t}\right)\\ ...\\ u_p={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{\mathrm{p\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{p\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{p\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{p\&theta;}}_n]\sin \left(\mathrm{p\&omega;t}\right)\end{array}\right.$

Calculate the 3rd time to the p time voltage total harmonic distortion:

$\mathrm{THD}=\frac{\sqrt{\underset{m=\mathrm{3,5,7}...}{\overset{p}{\mathrm{\&Sigma;}}}{u}_m^2}}{{\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1}$

Wherein, m=3,5,7 ..., p;

Judge whether the fundamental voltage value that calculates belongs in the benchmark fundamental voltage value scope that presets, and judge that whether the voltage total harmonic distortion that calculates is less than the reference voltage total harmonic distortion that presets; If the fundamental voltage value that calculates belongs in the benchmark fundamental voltage value scope that presets, and the voltage total harmonic distortion that calculates is less than the reference voltage total harmonic distortion that presets, the output voltage of then uncomfortable lay the grain volt battery, otherwise, the output voltage of adjustment photovoltaic cell.

Said reference fundamental voltage value scope and reference voltage total harmonic distortion are and set in advance, and for the technical indicator that this programme expectation reaches, if can't reach technical indicator, then carry out the adjustment of the output voltage of photovoltaic cell.After adjusting, rerun step 101, what obtain is adjusted output voltage, recomputates then, judges whether and need adjust once more.

The output voltage of above-mentioned adjustment photovoltaic cell can send to multi-electrical level inverter with adjusted output voltage for adjusting the output voltage of photovoltaic cell itself; Also can the output voltage that receive be adjusted for after multi-electrical level inverter receives the output voltage of photovoltaic cell.

Below the derivation of the angle of flow is described so that the reader understands the present invention theoretically, help enforcement of the present invention.Referring to Fig. 2 to Fig. 4.

Enumerate 4 staircase waveforms, set up staircase waveform normalization model.

$\left\{\begin{array}{c}{\mathrm{\&Delta;<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1={\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ {\mathrm{\&Delta;u}}_2=k_2-{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ {\mathrm{\&Delta;u}}_3=k_3-k_2\\ {\mathrm{\&Delta;<figure-callout\; id="4"\; label="u"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_4=k_4-k_3\\ {\mathrm{<figure-callout\; id="4"\; label="k"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">k</figure-callout>}}_4=1\end{array}\right.$

Determine the value constraints of the angle of flow.

$\left\{\begin{array}{c}0<{\mathrm{\&theta;}}_1<{\sin }^{-1}{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ {\sin }^{-1}{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1<{\mathrm{\&theta;}}_2<{\sin }^{-1}{k}_2\\ {\sin }^{-1}{k}_2<{\mathrm{\&theta;}}_3<{\sin }^{-1}{k}_3\\ {\sin }^{-1}{k}_3<{\mathrm{\&theta;}}_4<{\sin }^{-1}{\mathrm{<figure-callout\; id="4"\; label="k"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">k</figure-callout>}}_4=\frac{\mathrm{\&pi;}}{2}\end{array}\right.$

Deriving, a kind of On-line Control algorithm---entire area equates control algolithm.4 rank systems with Fig. 3 are the example analysis, and under the scale value situation, the sinusoidal wave area that surrounds with staircase waveform is respectively in (0-π) scope:

Make S ₁=S ₂, obtain:

-k ₁θ ₁+(k ₁-k ₂)θ ₂+(k ₂-k ₃)θ ₃+(k ₃-k ₄)θ ₄+90°＝180°/π

Be generalized to the N rank, obtain general formula and be:

-k ₁θ ₁+(k ₁-k ₂)θ ₂+…+(k _N-1-k _N)θ _N+90°＝180°/π

For the ease of peek, determine following principle:

θ _iSatisfy value constraints;

θ _i(i=2 ... N-1) be θ ₁Integral multiple or be taken at θ _{I-1, i}With θ _{I, i+1}The centre position;

θ _NDetermine by general formula;

0＜θ ₁＜sin ^-1(k ₁)＝sin ^-1(Δu ₁)。

Analyze the relation of the angle of flow and output harmonic wave, further determine θ _iThe value principle:

θ ₁Value at θ ₁₂/ 2, i.e. sin ^-1(Δ u ₁The left and right sides)/2 is proper;

θ _i(i=2 ... N-1) be taken at θ _{I-1, i}With θ _{I, i+1}Between, i.e. sin ^-1k _I-1With sin ^-1k _iBetween, electricity consumption pressure reduction is represented, promptly exists

With

Between;

Work as θ ₁～θ _N-1After determining, θ _NDetermine by general formula.

Embodiment two

Referring to Fig. 5 to Fig. 8, present embodiment with the sunlight photovoltaic generating system as an example.The cascaded multilevel inverter of present embodiment specifically refers to H bridge cascaded multilevel inverter.Suppose that three groups of photovoltaic cells are respectively U through the output voltage that the MPPT algorithm obtains _Dc1=120V, U _Dc2=150V, U _Dc3=170V, three groups of outputs are respectively three H bridge cascaded multilevel inverters and power.Utilize the staircase waveform stacking method can calculate these three groups of input voltages and can access 7 voltage steps, be respectively u ₁=120V, u ₂=150V, u ₃=170V, u ₄=270V, u ₅=290V, u ₆=320V, u ₇=u _Dcmax=440V.7 voltage steps are carried out normalized, obtain k ₁=0.27, k ₂=0.34, k ₃=0.39, k ₄=0.61, k ₅=0.66, k ₆=0.73, k ₇=1, according to above-mentioned formula 3, plateau voltage normalization difference DELTA u ₁～Δ u ₇Value is:

$\left\{\begin{array}{c}{\mathrm{\&Delta;<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1={\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1=0.27\\ {\mathrm{\&Delta;u}}_2=k_2-{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1=0.34-0.27=0.07\\ {\mathrm{\&Delta;u}}_3=k_3-k_2=0.39-0.34=0.05\\ {\mathrm{\&Delta;u}}_4=k_4-k_3=0.61-0.39=0.22\\ {\mathrm{\&Delta;u}}_5=k_6-{\mathrm{<figure-callout\; id="5"\; label="k"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">k</figure-callout>}}_5=0.66-0.61=0.05\\ {\mathrm{\&Delta;u}}_6=k_7-k_6=0.73-0.66=0.07\\ {\mathrm{\&Delta;u}}_7=1-k_7=1-0.73=0.27\end{array}\right.$

According to above-mentioned formula 6, conduction angle ₁～θ ₇Value constraints be:

According to above-mentioned formula 1, conduction angle ₁～θ ₆Be respectively:

With k ₁～k ₇With θ ₁～θ ₆Substitution formula 2:

Therefore obtain θ ₇=61.2 °.

With θ ₁～θ ₇And Δ u ₁～Δ u ₇ Value substitution formula 4, make m=1, calculate the fundamental voltage value:

If frequency is 2000Hz, can calculate the fundamental voltage value is 240.8V.

Make m=3,, calculate the 3rd subharmonic voltage value according to above-mentioned formula 7:

In like manner, can calculate the 5th, 7 ..., 39 times harmonic voltage value.Result of calculation reference table 1:

Harmonic number	1	3	5	7	9	11	13	15	17	19
											Amplitude	442.3	6.07	6.9	2.6	10.8	14.2	2.12	13.4	0.21	8.1
Harmonic number	21	23	25	27	29	31	33	35	37	39
											Amplitude	13	3.8	1.6	11	4.9	7.2	3.1	8.5	3.1	0.2

Table 1

According to formula 5, establish p=39, calculate the 3rd time to the p time voltage total harmonic distortion:

$\mathrm{THD}=\frac{\sqrt{\underset{n=\mathrm{3,5,7}...}{\overset{39}{\mathrm{\&Sigma;}}}{u}_m^2}}{{\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1}$

$=\frac{\sqrt{{6.07}^2+{6.9}^2+{2.6}^2+...+{0.2}^2}}{442.3}$

$=33.7/442.3$

$=7.61\%$

If in the technical indicator that sets in advance, benchmark fundamental voltage value scope is that (210V, 250V), the reference voltage total harmonic distortion is 10%.This example is judged fundamental voltage value and voltage total harmonic distortion simultaneously, to determine whether to need to adjust output voltage.Because the fundamental voltage value of this example belongs in the benchmark fundamental voltage value scope that presets, and the voltage total harmonic distortion is less than the reference voltage total harmonic distortion that presets, so do not need to adjust the output voltage of photovoltaic cell.

The present invention has widened the range of application of cascaded multilevel inverter; The range of application of cascaded multilevel inverter is extended to fields such as new forms of energy, combination UPS.The present invention has simplified the algorithm of trapezoidal wave superposing control cascaded multilevel inverter; Succinctly, the scope of application wide, simplified system design, engineering practicability is strong.The present invention can realize inverter control system in line computation, the control precision height, inverter output waveform quality is good.

Embodiment three

A kind of staircase waveform cascaded multilevel inverter comprises:

Voltage step acquiring unit is used to obtain the output voltage of photovoltaic cell, utilizes the staircase waveform stacking method to calculate the voltage step of output voltage, obtains the voltage of n voltage step; Wherein, n voltage step is respectively the 1st, 2 ..., i ..., n voltage step, the voltage of n voltage step is respectively u ₁, u ₂..., u _i..., u _n

Voltage step normalization unit is used for the voltage u to n voltage step ₁, u ₂..., u _i..., u _nCarry out normalized, obtain k ₁, k ₂..., k _i..., k _n, wherein, k _n=1;

Angle of flow computing unit is used to calculate the 1st, 2 ..., i ..., the conduction angle of n-1 voltage step ₁, θ ₂..., θ _i..., θ _N-1:

$\left\{\begin{array}{c}{\mathrm{\&theta;}}_1=\frac{{\sin }^{-1}\left(k_1\right)}{2}\\ {\mathrm{\&theta;}}_2=\frac{{\sin }^{-1}\left(k_2\right)+{\sin }^{-1}\left(k_3\right)}{2}\\ ......\\ {\mathrm{\&theta;}}_i=\frac{{\sin }^{-1}\left(k_i\right)+{\sin }^{-1}\left(k_{i+1}\right)}{2}\\ ......\\ {\mathrm{\&theta;}}_{n-1}=\frac{{\sin }^{-1}\left(k_{n-1}\right)+{\sin }^{-1}\left(k_n\right)}{2}\end{array}\right.$

Calculate the conduction angle of n voltage step _n:

-k ₁θ ₁+(k ₁-k ₂)θ ₂+…+(k _N-1-k _N)θ _N+90°＝180°/π

Wherein, the constraints of the angle of flow is:

$\left\{\begin{array}{c}0<{\mathrm{\&theta;}}_1<{\sin }^{-1}{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ {\sin }^{-1}{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1<{\mathrm{\&theta;}}_2<{\sin }^{-1}{k}_2\\ {\sin }^{-1}{k}_2<{\mathrm{\&theta;}}_3<{\sin }^{-1}{k}_3\\ ...\\ {\sin }^{-1}{k}_{i-1}<{\mathrm{\&theta;}}_i<{\sin }^{-1}{k}_i\\ ...\\ {\sin }^{-1}{k}_{n-1}<{\mathrm{\&theta;}}_n<{\sin }^{-1}{k}_n=\frac{\mathrm{\&pi;}}{2}\end{array}\right.$

Voltage step conducting control unit is used to utilize the conduction angle that calculates ₁, θ ₂..., θ _i..., θ _N-1, θ _n, control the 1st, 2 respectively ..., i ..., n-1, the conducting of n voltage step is with the output of the many level inputs becoming of direct current interchange level.

Preferably, voltage step acquiring unit comprises:

The output voltage acquiring unit is used to obtain the output voltage that j organizes photovoltaic cell, obtains j output voltage;

Voltage step computing unit is used to utilize the staircase waveform stacking method to calculate the voltage step of j output voltage, obtains the voltage of n voltage step, wherein, n voltage step is respectively the 1st, 2 ..., i, ..., n voltage step, the voltage of n voltage step is respectively u ₁, u ₂..., u _i..., u _n

Wherein, the quantity n of voltage step is:

For j output voltage carried out permutation and combination, n ₀Quantity for voltage step stack back equivalent voltage.

Present embodiment further comprises the output voltage adjustment unit, in the present embodiment, provides following three kinds of preferred implementations, and these three kinds of modes can be selected according to actual environment.

Optimal way one:

The output voltage adjustment unit is used to calculate plateau voltage normalization difference DELTA u ₁, Δ u ₂..., Δ u _i..., Δ u _n:

$\left\{\begin{array}{c}{\mathrm{\&Delta;<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1={\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ {\mathrm{\&Delta;u}}_2=k_2-{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ ...\\ {\mathrm{\&Delta;u}}_i=k_i-k_{i-1}\\ ...\\ {\mathrm{\&Delta;u}}_n=k_{n-1}-k_n\end{array}\right.$

The general formula of output voltage is:

$u_m=u_n\underset{m=\mathrm{1,3,5}...}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\frac{4}{\mathrm{m\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{m\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{m\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{m\&theta;}}_n]\sin m\left(\mathrm{\&omega;t}\right)$

Wherein, m=1,3,5 ...., ∞;

M gets 1 in the general formula, calculates the fundamental voltage value of output voltage:

${\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{\&theta;}}_n]\sin \left(\mathrm{\&omega;t}\right)$

Judge whether the fundamental voltage value that calculates belongs in the benchmark fundamental voltage value scope that presets, if, the output voltage of uncomfortable lay the grain volt battery, otherwise, the output voltage of adjustment photovoltaic cell.

Optimal way two:

The output voltage adjustment unit is used to calculate plateau voltage normalization difference DELTA u ₁, Δ u ₂..., Δ u _i..., Δ u _n:

$\left\{\begin{array}{c}{\mathrm{\&Delta;<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1={\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ {\mathrm{\&Delta;u}}_2=k_2-{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ ...\\ {\mathrm{\&Delta;u}}_i=k_i-k_{i-1}\\ ...\\ {\mathrm{\&Delta;u}}_n=k_{n-1}-k_n\end{array}\right.$

The general formula of output voltage is:

$u_m=u_n\underset{m=\mathrm{1,3,5}...}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\frac{4}{\mathrm{m\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{m\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{m\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{m\&theta;}}_n]\sin m\left(\mathrm{\&omega;t}\right)$

Wherein, m=1,3,5 ...., ∞;

M gets 1 in the general formula, calculates the fundamental voltage value of output voltage:

${\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{\&theta;}}_n]\sin \left(\mathrm{\&omega;t}\right)$

M gets 3,5,7 in the general formula ..., p; Calculate the 3rd, 5,7 of output voltage ..., p subharmonic voltage value, they are respectively u ₃, u ₅, u ₇..., u _p:

$\left\{\begin{array}{c}{u}_3={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{3\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 3\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 3\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 3\mathrm{\&theta;}}_n]\sin \left(3\mathrm{\&omega;t}\right)\\ {\mathrm{<figure-callout\; id="5"\; label="u"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">u</figure-callout>}}_5={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{5\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\mathrm{<figure-callout\; id="5"\; label="cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">cos</figure-callout>}5\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\mathrm{<figure-callout\; id="5"\; label="cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">cos</figure-callout>}5\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_{\mathrm{<figure-callout\; id="5"\; label="n\; cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">n</figure-callout>}}{\cos }_{}{5\mathrm{\&theta;}}_n]\sin \left(5\mathrm{\&omega;t}\right)\\ u_7={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{7\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 7\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 7\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 7\mathrm{\&theta;}}_n]\sin \left(7\mathrm{\&omega;t}\right)\\ ...\\ u_p={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{\mathrm{p\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{p\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{p\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{p\&theta;}}_n]\sin \left(\mathrm{p\&omega;t}\right)\end{array}\right.$

Calculate the 3rd time to the p time voltage total harmonic distortion:

$\mathrm{THD}=\frac{\sqrt{\underset{m=\mathrm{3,5,7}...}{\overset{p}{\mathrm{\&Sigma;}}}{u}_m^2}}{{\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1}$

Wherein, m=3,5,7 ..., p;

Whether judge the voltage total harmonic distortion that calculates less than the reference voltage total harmonic distortion that presets, if, the output voltage of uncomfortable lay the grain volt battery, otherwise, the output voltage of adjustment photovoltaic cell.

Optimal way three:

The output voltage adjustment unit is used to calculate plateau voltage normalization difference DELTA u ₁, Δ u ₂..., Δ u _i..., Δ u _n:

$\left\{\begin{array}{c}{\mathrm{\&Delta;<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1={\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ {\mathrm{\&Delta;u}}_2=k_2-{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\\ ...\\ {\mathrm{\&Delta;u}}_i=k_i-k_{i-1}\\ ...\\ {\mathrm{\&Delta;u}}_n=k_{n-1}-k_n\end{array}\right.$

The general formula of output voltage is:

$u_m=u_n\underset{m=\mathrm{1,3,5}...}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\frac{4}{\mathrm{m\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{m\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{m\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{m\&theta;}}_n]\sin m\left(\mathrm{\&omega;t}\right)$

Wherein, m=1,3,5 ...., ∞;

M gets 1 in the general formula, calculates the fundamental voltage value of output voltage:

${\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{\&theta;}}_n]\sin \left(\mathrm{\&omega;t}\right)$

M gets 3,5,7 in the general formula ..., p; Calculate the 3rd, 5,7 of output voltage ..., p subharmonic voltage value, they are respectively u ₃, u ₅, u ₇..., u _p:

$\left\{\begin{array}{c}{u}_3={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{3\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 3\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 3\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 3\mathrm{\&theta;}}_n]\sin \left(3\mathrm{\&omega;t}\right)\\ {\mathrm{<figure-callout\; id="5"\; label="u"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">u</figure-callout>}}_5={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{5\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\mathrm{<figure-callout\; id="5"\; label="cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">cos</figure-callout>}5\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\mathrm{<figure-callout\; id="5"\; label="cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">cos</figure-callout>}5\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_{\mathrm{<figure-callout\; id="5"\; label="n\; cos"\; filenames="H2009101941868E0000032.png,H2009101941868E0000033.png"\; state="\{\{state\}\}">n</figure-callout>}}{\cos }_{}{5\mathrm{\&theta;}}_n]\sin \left(5\mathrm{\&omega;t}\right)\\ u_7={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{7\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 7\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 7\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 7\mathrm{\&theta;}}_n]\sin \left(7\mathrm{\&omega;t}\right)\\ ...\\ u_p={\mathrm{<figure-callout\; id="4"\; label="u\; n"\; filenames="H2009101941868E0000021.png"\; state="\{\{state\}\}">u</figure-callout>}}_n\frac{4}{\mathrm{p\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{p\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{p\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{p\&theta;}}_n]\sin \left(\mathrm{p\&omega;t}\right)\end{array}\right.$

Calculate the 3rd time to the p time voltage total harmonic distortion:

$\mathrm{THD}=\frac{\sqrt{\underset{m=\mathrm{3,5,7}...}{\overset{p}{\mathrm{\&Sigma;}}}{u}_m^2}}{{\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="H2009101941868E0000031.png"\; state="\{\{state\}\}">u</figure-callout>}}_1}$

Wherein, m=3,5,7 ..., p;

If the fundamental voltage value that calculates belongs in the benchmark fundamental voltage value scope that presets, and the voltage total harmonic distortion that calculates is less than the reference voltage total harmonic distortion that presets, the output voltage of then uncomfortable lay the grain volt battery; Otherwise, the output voltage of adjustment photovoltaic cell.

Above-mentioned output voltage adjustment unit can send to multi-electrical level inverter with adjusted output voltage for adjusting the output voltage of photovoltaic cell itself to the adjustment of the output voltage of photovoltaic cell; Also can the output voltage that receive be adjusted for after multi-electrical level inverter receives the output voltage of photovoltaic cell.

Above content is preferred embodiment of the present invention only, and for those of ordinary skill in the art, according to thought of the present invention, the part that all can change in specific embodiments and applications, this description should not be construed as limitation of the present invention.

Claims (10)

1. the voltage step control method of the staircase waveform cascaded multilevel inverter that different voltages are differential is characterized in that, comprising:

A. obtain the output voltage of photovoltaic cell, utilize the staircase waveform stacking method to calculate the voltage step of described output voltage, obtain the voltage of n voltage step, wherein, n voltage step is respectively the 1st, 2 ..., i, ..., n voltage step, the voltage of n voltage step is respectively u ₁, u ₂..., u _i..., u _n

B. to the voltage u of n voltage step ₁, u ₂..., u _i..., u _nCarry out normalized, obtain k ₁, k ₂..., k _i..., k _n, wherein, k _n=1;

C. calculate the 1st, 2 ..., i ..., the conduction angle of n-1 voltage step ₁, θ ₂..., θ _i..., θ _N-1:

$\left\{\begin{array}{c}{\mathrm{\&theta;}}_1=\frac{{\sin }^{-1}\left(k_1\right)}{2}\\ {\mathrm{\&theta;}}_2=\frac{{\sin }^{-1}\left(k_2\right)+{\sin }^{-1}\left(k_3\right)}{2}\\ ......\\ {\mathrm{\&theta;}}_i=\frac{{\sin }^{-1}\left(k_i\right)+{\sin }^{-1}\left(k_{i+1}\right)}{2}\\ ......\\ {\mathrm{\&theta;}}_{n-1}=\frac{{\sin }^{-1}\left(k_{n-1}\right)+{\sin }^{-1}\left(k_n\right)}{2}\end{array}\right.$

D. calculate the conduction angle of n voltage step _n:

-k ₁θ ₁+(k ₁-k ₂)θ ₂+…+(k _N-1-k _N)θ _N+90°＝180°/π

Wherein, the constraints of the angle of flow is:

$\left\{\begin{array}{c}0<{\mathrm{\&theta;}}_1<{\sin }^{-1}{k}_1\\ {\sin }^{-1}{k}_1<{\mathrm{\&theta;}}_2<{\sin }^{-1}{k}_2\\ {\sin }^{-1}{k}_2<{\mathrm{\&theta;}}_3<{\sin }^{-1}{k}_3\\ ...\\ {\sin }^{-1}{k}_{i-1}<{\mathrm{\&theta;}}_i<{\sin }^{-1}{k}_i\\ ...\\ {\sin }^{-1}{k}_{n-1}<{\mathrm{\&theta;}}_n<{\sin }^{-1}{k}_n=\frac{\mathrm{\&pi;}}{2}\end{array}\right.$

E. utilize the conduction angle that calculates ₁, θ ₂..., θ _i..., θ _N-1, θ _n, control the 1st, 2 respectively ..., i ..., n-1, the conducting of n voltage step is with the output of the many level inputs becoming of direct current interchange level.

2. the voltage step control method of the staircase waveform cascaded multilevel inverter that different voltages according to claim 1 are differential is characterized in that steps A specifically comprises:

Obtain the output voltage of j group photovoltaic cell, obtain j output voltage;

Utilize the staircase waveform stacking method to calculate the voltage step of a described j output voltage, obtain the voltage of n voltage step, wherein, n voltage step is respectively the 1st, 2 ..., i ..., n voltage step, the voltage of n voltage step is respectively u ₁, u ₂..., u _i..., u _n

Wherein, the quantity n of voltage step is:

For j output voltage carried out permutation and combination, n ₀Quantity for voltage step stack back equivalent voltage.

3. the voltage step control method of the staircase waveform cascaded multilevel inverter that different voltages according to claim 1 are differential is characterized in that, after the described step D, further comprises step F:

Calculate plateau voltage normalization difference DELTA u ₁, Δ u ₂..., Δ u _i..., Δ u _n:

$\left\{\begin{array}{c}{\mathrm{\&Delta;u}}_1=k_1\\ {\mathrm{\&Delta;u}}_2=k_2-k_1\\ ...\\ {\mathrm{\&Delta;u}}_i=k_i-k_{i-1}\\ ...\\ {\mathrm{\&Delta;u}}_n=k_{n-1}-k_n\end{array}\right.$

The general formula of output voltage is:

$u_m=u_n\underset{m=\mathrm{1,3,5}...}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\frac{4}{\mathrm{m\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{m\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{m\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{m\&theta;}}_n]\sin m\left(\mathrm{\&omega;t}\right)$

Wherein, m=1,3,5 ...., ∞;

M gets 1 in the described general formula, calculates the fundamental voltage value of output voltage:

$u_1=u_n\frac{4}{\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{\&theta;}}_n]\sin \left(\mathrm{\&omega;t}\right)$

Judge whether the described fundamental voltage value that calculates belongs in the benchmark fundamental voltage value scope that presets, if, the output voltage of uncomfortable lay the grain volt battery, otherwise, the output voltage of adjustment photovoltaic cell.

4. the voltage step control method of the staircase waveform cascaded multilevel inverter that different voltages according to claim 1 are differential is characterized in that, after the described step D, further comprises step F:

Calculate plateau voltage normalization difference DELTA u ₁, Δ u ₂..., Δ u _i..., Δ u _n:

$\left\{\begin{array}{c}{\mathrm{\&Delta;u}}_1=k_1\\ {\mathrm{\&Delta;u}}_2=k_2-k_1\\ ...\\ {\mathrm{\&Delta;u}}_i=k_i-k_{i-1}\\ ...\\ {\mathrm{\&Delta;u}}_n=k_{n-1}-k_n\end{array}\right.$

The general formula of output voltage is:

$u_m=u_n\underset{m=\mathrm{1,3,5}...}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\frac{4}{\mathrm{m\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{m\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{m\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{m\&theta;}}_n]\sin m\left(\mathrm{\&omega;t}\right)$

Wherein, m=1,3,5 ...., ∞;

M gets 1 in the general formula, calculates the fundamental voltage value of output voltage:

$u_1=u_n\frac{4}{\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{\&theta;}}_n]\sin \left(\mathrm{\&omega;t}\right)$

M gets 3,5,7 in the general formula ..., p; Calculate the 3rd, 5,7 of output voltage ..., p subharmonic voltage value, they are respectively u ₃, u ₅, u ₇..., u _p:

$\left\{\begin{array}{c}{u}_3=u_n\frac{4}{3\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 3\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 3\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 3\mathrm{\&theta;}}_n]\sin \left(3\mathrm{\&omega;t}\right)\\ u_5=u_n\frac{4}{5\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 5\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 5\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 5\mathrm{\&theta;}}_n]\sin \left(5\mathrm{\&omega;t}\right)\\ u_7=u_n\frac{4}{7\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 7\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 7\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 7\mathrm{\&theta;}}_n]\sin \left(7\mathrm{\&omega;t}\right)\\ ...\\ u_p=u_n\frac{4}{\mathrm{p\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{p\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{p\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{p\&theta;}}_n]\sin \left(\mathrm{p\&omega;t}\right)\end{array}\right.$

Calculate the 3rd time to the p time voltage total harmonic distortion:

$\mathrm{THD}=\frac{\sqrt{\underset{m=\mathrm{3,5,7}...}{\overset{p}{\mathrm{\&Sigma;}}}{u}_m^2}}{u_1}$

Wherein, m=3,5,7 ..., p;

Whether judge the described voltage total harmonic distortion that calculates less than the reference voltage total harmonic distortion that presets, if, the output voltage of uncomfortable lay the grain volt battery, otherwise, the output voltage of adjustment photovoltaic cell.

5. the voltage step control method of the staircase waveform cascaded multilevel inverter that different voltages according to claim 1 are differential is characterized in that, after the described step D, further comprises step F:

Calculate plateau voltage normalization difference DELTA u ₁, Δ u ₂..., Δ u _i..., Δ u _n:

$\left\{\begin{array}{c}{\mathrm{\&Delta;u}}_1=k_1\\ {\mathrm{\&Delta;u}}_2=k_2-k_1\\ ...\\ {\mathrm{\&Delta;u}}_i=k_i-k_{i-1}\\ ...\\ {\mathrm{\&Delta;u}}_n=k_{n-1}-k_n\end{array}\right.$

The general formula of output voltage is:

$u_m=u_n\underset{m=\mathrm{1,3,5}...}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\frac{4}{\mathrm{m\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{m\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{m\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{m\&theta;}}_n]\sin m\left(\mathrm{\&omega;t}\right)$

Wherein, m=1,3,5 ...., ∞;

M gets 1 in the general formula, calculates the fundamental voltage value of output voltage:

$u_1=u_n\frac{4}{\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{\&theta;}}_n]\sin \left(\mathrm{\&omega;t}\right)$

M gets 3,5,7 in the general formula ..., p; Calculate the 3rd, 5,7 of output voltage ..., p subharmonic voltage value, they are respectively u ₃, u ₅, u ₇..., u _p:

$\left\{\begin{array}{c}{u}_3=u_n\frac{4}{3\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 3\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 3\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 3\mathrm{\&theta;}}_n]\sin \left(3\mathrm{\&omega;t}\right)\\ u_5=u_n\frac{4}{5\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 5\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 5\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 5\mathrm{\&theta;}}_n]\sin \left(5\mathrm{\&omega;t}\right)\\ u_7=u_n\frac{4}{7\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 7\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 7\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 7\mathrm{\&theta;}}_n]\sin \left(7\mathrm{\&omega;t}\right)\\ ...\\ u_p=u_n\frac{4}{\mathrm{p\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{p\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{p\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{p\&theta;}}_n]\sin \left(\mathrm{p\&omega;t}\right)\end{array}\right.$

Calculate the 3rd time to the p time voltage total harmonic distortion:

$\mathrm{THD}=\frac{\sqrt{\underset{m=\mathrm{3,5,7}...}{\overset{p}{\mathrm{\&Sigma;}}}{u}_m^2}}{u_1}$

Wherein, m=3,5,7 ..., p;

If the described fundamental voltage value that calculates belongs in the benchmark fundamental voltage value scope that presets, and the described voltage total harmonic distortion that calculates is less than the reference voltage total harmonic distortion that presets, the output voltage of then uncomfortable lay the grain volt battery; Otherwise, the output voltage of adjustment photovoltaic cell.

6. a staircase waveform cascaded multilevel inverter is characterized in that, comprising:

Voltage step acquiring unit is used to obtain the output voltage of photovoltaic cell, utilizes the staircase waveform stacking method to calculate the voltage step of described output voltage, obtains the voltage of n voltage step; Wherein, n voltage step is respectively the 1st, 2 ..., i ..., n voltage step, the voltage of n voltage step is respectively u ₁, u ₂..., u _i..., u _n

Voltage step normalization unit is used for the voltage u to n voltage step ₁, u ₂..., u _i..., u _nCarry out normalized, obtain k ₁, k ₂..., k _i..., k _n, wherein, k _n=1;

Angle of flow computing unit is used to calculate the 1st, 2 ..., i ..., the conduction angle of n-1 voltage step ₁, θ ₂..., θ _i..., θ _N-1:

$\left\{\begin{array}{c}{\mathrm{\&theta;}}_1=\frac{{\sin }^{-1}\left(k_1\right)}{2}\\ {\mathrm{\&theta;}}_2=\frac{{\sin }^{-1}\left(k_2\right)+{\sin }^{-1}\left(k_3\right)}{2}\\ ......\\ {\mathrm{\&theta;}}_i=\frac{{\sin }^{-1}\left(k_i\right)+{\sin }^{-1}\left(k_{i+1}\right)}{2}\\ ......\\ {\mathrm{\&theta;}}_{n-1}=\frac{{\sin }^{-1}\left(k_{n-1}\right)+{\sin }^{-1}\left(k_n\right)}{2}\end{array}\right.$

Calculate the conduction angle of n voltage step _n:

-k ₁θ ₁+(k ₁-k ₂)θ ₂+…+(k _N-1-k _N)θ _N+90°＝180°/π

Wherein, the constraints of the angle of flow is:

$\left\{\begin{array}{c}0<{\mathrm{\&theta;}}_1<{\sin }^{-1}{k}_1\\ {\sin }^{-1}{k}_1<{\mathrm{\&theta;}}_2<{\sin }^{-1}{k}_2\\ {\sin }^{-1}{k}_2<{\mathrm{\&theta;}}_3<{\sin }^{-1}{k}_3\\ ...\\ {\sin }^{-1}{k}_{i-1}<{\mathrm{\&theta;}}_i<{\sin }^{-1}{k}_i\\ ...\\ {\sin }^{-1}{k}_{n-1}<{\mathrm{\&theta;}}_n<{\sin }^{-1}{k}_n=\frac{\mathrm{\&pi;}}{2}\end{array}\right.$

Voltage step conducting control unit is used to utilize the conduction angle that calculates ₁, θ ₂..., θ _i..., θ _N-1, θ _n, control the 1st, 2 respectively ..., i ..., n-1, the conducting of n voltage step is with the output of the many level inputs becoming of direct current interchange level.

7. staircase waveform cascaded multilevel inverter according to claim 6 is characterized in that, described voltage step acquiring unit comprises:

The output voltage acquiring unit is used to obtain the output voltage that j organizes photovoltaic cell, obtains j output voltage;

Voltage step computing unit is used to utilize the staircase waveform stacking method to calculate the voltage step of a described j output voltage, obtains the voltage of n voltage step, wherein, n voltage step is respectively the 1st, 2 ..., i, ..., n voltage step, the voltage of n voltage step is respectively u ₁, u ₂..., u _i..., u _n

Wherein, the quantity n of voltage step is:

For j output voltage carried out permutation and combination, n ₀Quantity for voltage step stack back equivalent voltage.

8. staircase waveform cascaded multilevel inverter according to claim 6 is characterized in that, further comprises the output voltage adjustment unit;

The output voltage adjustment unit is used to calculate plateau voltage normalization difference DELTA u ₁, Δ u ₂..., Δ u _i..., Δ u _n:

$\left\{\begin{array}{c}{\mathrm{\&Delta;u}}_1=k_1\\ {\mathrm{\&Delta;u}}_2=k_2-k_1\\ ...\\ {\mathrm{\&Delta;u}}_i=k_i-k_{i-1}\\ ...\\ {\mathrm{\&Delta;u}}_n=k_{n-1}-k_n\end{array}\right.$

The general formula of output voltage is:

$u_m=u_n\underset{m=\mathrm{1,3,5}...}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\frac{4}{\mathrm{m\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{m\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{m\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{m\&theta;}}_n]\sin m\left(\mathrm{\&omega;t}\right)$

Wherein, m=1,3,5 ...., ∞;

M gets 1 in the described general formula, calculates the fundamental voltage value of output voltage:

$u_1=u_n\frac{4}{\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{\&theta;}}_n]\sin \left(\mathrm{\&omega;t}\right)$

Judge whether the described fundamental voltage value that calculates belongs in the benchmark fundamental voltage value scope that presets, if, the output voltage of uncomfortable lay the grain volt battery, otherwise, the output voltage of adjustment photovoltaic cell.

9. staircase waveform cascaded multilevel inverter according to claim 6 is characterized in that, further comprises the output voltage adjustment unit;

The output voltage adjustment unit is used to calculate plateau voltage normalization difference DELTA u ₁, Δ u ₂..., Δ u _i..., Δ u _n:

$\left\{\begin{array}{c}{\mathrm{\&Delta;u}}_1=k_1\\ {\mathrm{\&Delta;u}}_2=k_2-k_1\\ ...\\ {\mathrm{\&Delta;u}}_i=k_i-k_{i-1}\\ ...\\ {\mathrm{\&Delta;u}}_n=k_{n-1}-k_n\end{array}\right.$

The general formula of output voltage is:

$u_m=u_n\underset{m=\mathrm{1,3,5}...}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\frac{4}{\mathrm{m\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{m\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{m\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{m\&theta;}}_n]\sin m\left(\mathrm{\&omega;t}\right)$

Wherein, m=1,3,5 ...., ∞;

M gets 1 in the general formula, calculates the fundamental voltage value of output voltage:

$u_1=u_n\frac{4}{\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{\&theta;}}_n]\sin \left(\mathrm{\&omega;t}\right)$

M gets 3,5,7 in the general formula ..., p; Calculate the 3rd, 5,7 of output voltage ..., p subharmonic voltage value, they are respectively u ₃, u ₅, u ₇..., u _p:

$\left\{\begin{array}{c}{u}_3=u_n\frac{4}{3\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 3\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 3\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 3\mathrm{\&theta;}}_n]\sin \left(3\mathrm{\&omega;t}\right)\\ u_5=u_n\frac{4}{5\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 5\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 5\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 5\mathrm{\&theta;}}_n]\sin \left(5\mathrm{\&omega;t}\right)\\ u_7=u_n\frac{4}{7\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 7\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 7\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 7\mathrm{\&theta;}}_n]\sin \left(7\mathrm{\&omega;t}\right)\\ ...\\ u_p=u_n\frac{4}{\mathrm{p\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{p\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{p\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{p\&theta;}}_n]\sin \left(\mathrm{p\&omega;t}\right)\end{array}\right.$

Calculate the 3rd time to the p time voltage total harmonic distortion:

$\mathrm{THD}=\frac{\sqrt{\underset{m=\mathrm{3,5,7}...}{\overset{p}{\mathrm{\&Sigma;}}}{u}_m^2}}{u_1}$

Wherein, m=3,5,7 ..., p;

Whether judge the described voltage total harmonic distortion that calculates less than the reference voltage total harmonic distortion that presets, if, the output voltage of uncomfortable lay the grain volt battery, otherwise, the output voltage of adjustment photovoltaic cell.

10. staircase waveform cascaded multilevel inverter according to claim 6 is characterized in that, further comprises the output voltage adjustment unit;

The output voltage adjustment unit is used to calculate plateau voltage normalization difference DELTA u ₁, Δ u ₂..., Δ u _i..., Δ u _n:

$\left\{\begin{array}{c}{\mathrm{\&Delta;u}}_1=k_1\\ {\mathrm{\&Delta;u}}_2=k_2-k_1\\ ...\\ {\mathrm{\&Delta;u}}_i=k_i-k_{i-1}\\ ...\\ {\mathrm{\&Delta;u}}_n=k_{n-1}-k_n\end{array}\right.$

The general formula of output voltage is:

$u_m=u_n\underset{m=\mathrm{1,3,5}...}{\overset{\&infin;}{\mathrm{\&Sigma;}}}\frac{4}{\mathrm{m\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{m\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{m\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{m\&theta;}}_n]\sin m\left(\mathrm{\&omega;t}\right)$

Wherein, m=1,3,5 ...., ∞;

M gets 1 in the general formula, calculates the fundamental voltage value of output voltage:

$u_1=u_n\frac{4}{\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{\&theta;}}_n]\sin \left(\mathrm{\&omega;t}\right)$

M gets 3,5,7 in the general formula ..., p; Calculate the 3rd, 5,7 of output voltage ..., p subharmonic voltage value, they are respectively u ₃, u ₅, u ₇..., u _p:

$\left\{\begin{array}{c}{u}_3=u_n\frac{4}{3\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 3\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 3\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 3\mathrm{\&theta;}}_n]\sin \left(3\mathrm{\&omega;t}\right)\\ u_5=u_n\frac{4}{5\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 5\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 5\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 5\mathrm{\&theta;}}_n]\sin \left(5\mathrm{\&omega;t}\right)\\ u_7=u_n\frac{4}{7\mathrm{\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos 7\mathrm{\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos 7\mathrm{\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos 7\mathrm{\&theta;}}_n]\sin \left(7\mathrm{\&omega;t}\right)\\ ...\\ u_p=u_n\frac{4}{\mathrm{p\&pi;}}[{\mathrm{\&Delta;u}}_1{\cos \mathrm{p\&theta;}}_1+{\mathrm{\&Delta;u}}_2{\cos \mathrm{p\&theta;}}_2+...+{\mathrm{\&Delta;u}}_n{\cos \mathrm{p\&theta;}}_n]\sin \left(\mathrm{p\&omega;t}\right)\end{array}\right.$

Calculate the 3rd time to the p time voltage total harmonic distortion:

$\mathrm{THD}=\frac{\sqrt{\underset{m=\mathrm{3,5,7}...}{\overset{p}{\mathrm{\&Sigma;}}}{u}_m^2}}{u_1}$

Wherein, m=3,5,7 ..., p;

If the described fundamental voltage value that calculates belongs in the benchmark fundamental voltage value scope that presets, and the described voltage total harmonic distortion that calculates is less than the reference voltage total harmonic distortion that presets, the output voltage of then uncomfortable lay the grain volt battery; Otherwise, the output voltage of adjustment photovoltaic cell.

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