【摘要】：在大功率電力電子裝置的研究和應(yīng)用領(lǐng)域,多電平變換器因其比兩電平變換器具有更好的輸出電壓波形和可獲取更高的電壓等級等突出優(yōu)點(diǎn)而廣受關(guān)注,已成為一種代表性的解決方案。然而目前并沒有一種完美的多電平變換器拓?fù)?現(xiàn)有的拓?fù)湓趯?shí)際應(yīng)用中均存在一定的局限性。二極管鉗位型逆變器既不需要多個(gè)獨(dú)立的直流電源,也不需要笨重的電容及其預(yù)充電系統(tǒng),同時(shí)還具有開關(guān)控制易于實(shí)現(xiàn)、保護(hù)電路簡單等優(yōu)點(diǎn)。對這一拓?fù)涞膽?yīng)用造成阻礙的是其直流側(cè)分壓電容在逆變器運(yùn)行時(shí)會發(fā)生電壓偏移,使得逆變器性能下降甚至不能正常工作。本文的工作就致力于從調(diào)制方案這一硬件結(jié)構(gòu)最簡單同時(shí)也最節(jié)省系統(tǒng)成本的途徑來研究解決多電平二極管鉗位逆變器的直流電容電壓偏移問題。 論文分析了傳統(tǒng)SVM算法在多電平二極管鉗位逆變器中實(shí)現(xiàn)的原理和步驟,指出了傳統(tǒng)SVM算法需要進(jìn)行大量三角函數(shù)運(yùn)算或查表操作、因而運(yùn)算效率低的不足。通過引入基于Kohonen競爭性神經(jīng)網(wǎng)絡(luò)的分類算法,提出了一種改進(jìn)的多電平二極管鉗位逆變器SVM算法。改進(jìn)的算法并不需要對神經(jīng)網(wǎng)絡(luò)進(jìn)行訓(xùn)練,在整個(gè)實(shí)現(xiàn)過程中不再需要任何三角函數(shù)計(jì)算或查表操作,而只需要進(jìn)行簡單的四則運(yùn)算,所節(jié)省的運(yùn)算時(shí)間可用于完成其他耗時(shí)的工作如實(shí)現(xiàn)電容電壓均壓等。對三電平和五電平的二極管鉗位逆變器進(jìn)行時(shí)域仿真,結(jié)果驗(yàn)證了文中數(shù)學(xué)分析的正確性和所提算法的可行性,同時(shí)表明改進(jìn)的算法是一種對多電平二極管鉗位逆變器通用的算法,將它應(yīng)用于不同電平數(shù)的逆變器時(shí)不需要進(jìn)行任何修改。 為了能夠利用調(diào)制算法消除多電平二極管鉗位逆變器直流電容電壓的偏移,論文從理論上對這一現(xiàn)象產(chǎn)生的原因進(jìn)行了深入的分析。首先研究了三電平二極管鉗位逆變器的調(diào)制矢量的特點(diǎn),通過具體的圖例分析了四類調(diào)制矢量對中點(diǎn)電位的影響,明確了三電平二極管鉗位逆變器能夠利用小矢量調(diào)節(jié)電容的電壓。其次以五電平二極管鉗位逆變器為例分析了電平數(shù)超過3時(shí)的多電平逆變器的電容電壓偏移問題,分析表明這類拓?fù)錈o法在全調(diào)制比范圍內(nèi)利用小矢量控制電容電壓。由于逆變器直流側(cè)電容電流平均值為零時(shí),直流電容電壓才能保持平衡,因此推導(dǎo)出在SPWM調(diào)制算法下五電平二極管鉗位逆變器直流側(cè)電容電流平均值與調(diào)制比和交流側(cè)功率因數(shù)之間的函數(shù)關(guān)系。分析結(jié)果說明在不采用輔助電路的情況下,傳統(tǒng)的SPWM技術(shù)不能維持直流電容電壓平衡；但SVM方法卻有可能利用冗余開關(guān)狀態(tài)、在不設(shè)置輔助硬件的前提下實(shí)現(xiàn)直流側(cè)電容均壓。在分析電容電壓偏移的本質(zhì)原因的基礎(chǔ)上,說明了無論采用哪種PWM算法來維持多電平二極管鉗位逆變器的電容電壓,都存在一個(gè)由調(diào)制比和交流側(cè)功率因數(shù)所限定的穩(wěn)定運(yùn)行范圍,因而電容電壓平衡SVM算法主要適合應(yīng)用于二極管鉗位逆變器進(jìn)行無功功率交換的場合。 根據(jù)多電平二極管鉗位逆變器的最小能量特性建立了五電平逆變器的能量函數(shù),研究了通過能量函數(shù)來選擇恰當(dāng)?shù)娜哂嚅_關(guān)狀態(tài)從而實(shí)現(xiàn)電容均壓的方法。為了計(jì)算在不同開關(guān)狀態(tài)下的能量函數(shù)值,推導(dǎo)了逆變器中間支路電流平均值與各個(gè)扇區(qū)開關(guān)狀態(tài)之間的關(guān)系,得到了五電平二極管鉗位逆變器的綜合電流數(shù)學(xué)模型。在此基礎(chǔ)上建立了多電平二極管鉗位逆變器的通用電流模型,從而得到了對任意電平通用的電容電壓平衡SVM算法。仿真研究表明基于能量函數(shù)的電容電壓平衡算法能夠在對稱負(fù)載、不對稱負(fù)載和畸變負(fù)載等穩(wěn)態(tài)條件下使得偏離的電容電壓回歸到標(biāo)準(zhǔn)值。 基于能量函數(shù)的平衡算法計(jì)算量非常大,且未考慮對開關(guān)頻率的優(yōu)化,因而不可避免地造成逆變器運(yùn)行時(shí)開關(guān)頻率較大。針對該算法的不足,本文提出了種新的基于有功電流的SVM算法。新算法利用有功電流來判斷二極管鉗位逆變器交流側(cè)的能量傳輸方向,通過分析能量傳輸方向與不同的開關(guān)序列對電容電壓的影響,從一組預(yù)定義的開關(guān)序列中選取使得偏離標(biāo)準(zhǔn)值最多的電容電壓盡可能回歸標(biāo)準(zhǔn)值的開關(guān)序列。新算法使逆變器在運(yùn)行中擺脫了大量的乘法運(yùn)算,只需幾次比較運(yùn)算就能得出調(diào)制結(jié)果,大大降低了運(yùn)算量、提高了調(diào)制速度；同時(shí)算法對開關(guān)器件工作頻率進(jìn)行了優(yōu)化,使得在一個(gè)開關(guān)周期內(nèi)的器件開關(guān)次數(shù)最少,能有效降低開關(guān)頻率從而降低開關(guān)損耗。大量不同工況下的仿真研究證明了基于有功電流算法的有效性以及它的性能優(yōu)勢。 為了進(jìn)一步考察電容電壓平衡算法的應(yīng)用效果,本文研究了一個(gè)基于五電平二極管鉗位逆變器的STATCOM系統(tǒng)。該STATCOM的直流側(cè)電容沒有輔助平衡電路,它是完全依賴空間矢量調(diào)制算法來控制電容電壓的。建立了STATCOM的數(shù)學(xué)模型,在此模型的基礎(chǔ)上分別設(shè)計(jì)STATCOM交流側(cè)電流控制器、直流端電壓控制器和公共連接點(diǎn)電壓控制器,再將控制器與電容電壓平衡算法相結(jié)合,構(gòu)成了完整的STATCOM控制系統(tǒng)。對STATCOM系統(tǒng)的性能進(jìn)行了仿真研究,結(jié)果表明STATCOM的控制器能有效的控制STATCOM輸出的無功功率、直流端電壓和公共連接點(diǎn)電壓。對基于能量函數(shù)和基于有功電流的電容電流平衡算法的性能進(jìn)行了仿真對比,結(jié)果證明兩種算法都能有效的在穩(wěn)態(tài)和動態(tài)條件下將五電平二極管鉗位逆變器的直流電容電壓維持在標(biāo)準(zhǔn)值,但本文提出的基于有功電流的算法具有更好的動態(tài)性能。
[Abstract]:In the field of research and application of high-power power electronic devices, multilevel converters have become a representative solution because of their outstanding advantages of better output voltage waveform and higher voltage level than two level converters. However, there is no perfect multilevel converter topology at present. The existing topology has some limitations in practical application. The diode clamped inverter does not need multiple independent DC power supply, and does not need heavy capacitance and precharging system. It also has the advantages of easy switching control and simple protection circuit. The application of this topology is hindering its DC side. The voltage offset of the voltage divider will occur during the operation of the inverter so that the performance of the inverter can not even work normally. The work of this paper is devoted to the study of the problem of DC capacitance voltage offset from the simplest hardware structure and the most systematic cost saving of the modulation scheme.
The paper analyzes the principle and steps of the traditional SVM algorithm in the multilevel diode clamped inverter, and points out that the traditional SVM algorithm needs to perform a large number of trigonometric functions or look-up operations, so the operation efficiency is low. By introducing a classification algorithm based on Kohonen competitive neural network, an improved multilevel two is proposed. SVM algorithm of pole position inverter. The improved algorithm does not need to train the neural network. It does not need any trigonometric function calculation or look-up operation in the whole implementation process, but only requires four simple operations. The saving time can be used to complete other time-consuming tasks such as the realization of capacitor voltage mean voltage and so on. Three The level and five level diode clamped inverter is simulated in time domain. The results verify the correctness of the mathematical analysis and the feasibility of the proposed algorithm. At the same time, it shows that the improved algorithm is a common algorithm for multilevel diode clamped inverters. It does not require any modification when the inverter is used for different level number inverters.
In order to use the modulation algorithm to eliminate the offset of the DC capacitance voltage of the multilevel diode clamped inverter, the paper theoretically analyzes the cause of this phenomenon. First, the modulation vector characteristics of the three level diode clamped inverter are studied, and the four kinds of modulation vector pairs are analyzed by specific illustrations. The effect of point potential is made clear that three level diode clamp inverters can use small vector to adjust the voltage of capacitance. Secondly, five level diode clamp inverter is used as an example to analyze the capacitance voltage offset of multilevel inverters when the number of level exceeds 3. The analysis shows that this type of extension can not use small vector in the range of total modulation ratio. The capacitor voltage is controlled. The DC capacitor voltage can be balanced because the average current of the capacitor current of the DC side of the inverter is zero. Therefore, the function relationship between the average value of the capacitance current of the DC side of the five level diode clamped inverter under the SPWM modulation algorithm and the modulation ratio and the power factor of the AC side is deduced. In the case of the auxiliary circuit, the traditional SPWM technology can not maintain the DC capacitor voltage balance, but the SVM method may make use of the state of redundant switch to realize the DC side capacitor voltage without setting the auxiliary hardware. Based on the analysis of the essential reason of the capacitance voltage offset, it shows that no matter which PWM algorithm is used to maintain more, the capacitor voltage is maintained. The capacitor voltage of the level diode clamp inverter has a stable operating range limited by the modulation ratio and the AC side power factor, so the capacitor voltage balance SVM algorithm is mainly suitable for the occasion of the reactive power switching of the diode clamper inverter.
According to the minimum energy characteristic of the multilevel diode clamper inverter, the energy function of the five level inverter is established. The method of capacitive voltage sharing is realized by selecting the appropriate redundant switch state through the energy function. In order to calculate the energy function value in different switching states, the average current average of the middle branch of the inverter is derived. The relationship between the value and the switching state of each sector is obtained, and a comprehensive current mathematical model of the five level diode clamp inverter is obtained. On this basis, a general current model of the multilevel diode clamped inverter is established, and the SVM algorithm for the general capacitance voltage balance of any level is obtained. The simulation study shows that the energy function is based on the energy function. The capacitor voltage balancing algorithm can make the deviated capacitor voltage regress to the standard value under symmetrical conditions such as symmetrical load, asymmetrical load and distorted load.
The calculation of the balance algorithm based on the energy function is very large and does not consider the optimization of the switching frequency. Therefore, the switching frequency of the inverter is unavoidable. In this paper, a new SVM algorithm based on active current is proposed in this paper. The new algorithm uses active current to judge the communication of diode clamped inverter. The direction of the energy transmission in the side, by analyzing the influence of the energy transmission direction and the different switch sequence on the capacitance voltage, from a set of predefined switch sequences, the switching sequence which makes the capacitor voltage that deviates the most standard value is as much as possible to the standard value is selected. The modulation results can be obtained by several comparison operations, which greatly reduces the amount of operation and improves the modulation speed. At the same time, the algorithm optimizes the working frequency of the switch device, making the switching frequency of the device in a switching period least, reducing the switching frequency and reducing the switching loss effectively. A large number of simulation studies under different working conditions have proved that The effectiveness of active current algorithm and its performance advantages are also discussed.
In order to further investigate the application effect of the capacitor voltage balance algorithm, a STATCOM system based on five level diode clamped inverter is studied. The DC side capacitance of the STATCOM has no auxiliary balance circuit. It is completely dependent on the space vector modulation algorithm to control the electrical voltage of the capacitor. The mathematical model of the STATCOM is established, and the model is established in this model. On the basis of the model, the STATCOM AC side current controller, the DC voltage controller and the common connection point voltage controller are separately designed. The integrated STATCOM control system is formed by combining the controller with the capacitor voltage balance algorithm. The performance of the STATCOM system is simulated. The results show that the STATCOM controller can be effective. The reactive power, DC end voltage and common connection point voltage of the STATCOM output are controlled. The performance of the capacitive current balancing algorithm based on the energy function and the active current is simulated and compared. The results show that the two algorithms are effective for the DC capacitor voltage of the five flat diode clamped inverter under steady and dynamic conditions. It is maintained at the standard value, but the algorithm based on active current in this paper has better dynamic performance.
【學(xué)位授予單位】：湖南大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2014
【分類號】：TM464

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