單相SPWM逆變器并聯(lián)解耦控制策略

1、精選優(yōu)質(zhì)文檔-傾情為你奉上英文資料原文來源: 出自JOURNAL OF ELECTRONIC SCIENCE AND TECHNOLOGY OF CHINA,VOL.7,NO.3, SEPTEMBER 2009Decoupling Control Strategy for Single Phase SPWM Parallel InvertersShun-Gang Xu,Jian-Ping Xu,and Tai-Qiang CaoAbstract: A decoupling control strategy of inverter parallel system is proposed base

2、d on the equivalent output impedance of single phase voltage source SPWM (sinusoidal pulse width modulation) inverter. The active power and reactive power are calculated in terms of output voltage and current of the inverter, and sent to the other inverters in the parallel system via controller area

3、 network(CAN)bus. By calculating and decoupling the circumfluence of the active power and reactive power, the inverters can share load current via the regulation of the reference-signal phase and amplitude.Experimental results of an 110V/2kVA inverter parallel system show the feasibility of the deco

4、upling control strategy.Index Terms-CAN bus, current sharing, inverters, parallel operation.1. IntroductionParallel operation of inverters is an efficient way to enhance the capacity and reliability of inverter systems. The key issue of parallel operation is the distribution of the load current. In

5、an inverter parallel system, the amplitudes and phases of output voltages of all inverters should strictly equal to each other to guarantee that each inverter shares the same load current. Otherwise, the current circumfluence and overload of some inverters in the inverter parallel system may exist.

6、The current circumfluence may also decrease the efficiency and reliability of the inverter parallel system.There are various techniques for the control of inverter parallel operation. Among these techniques, central control and master-slave control are easy to implement and have good current-sharing

7、 performance. However, these two control strategies work at the cost of system reliability because of conjunction operation among inverters.In instantaneous-current control of inverter parallel system, there is a current bus to share the current signal among inverters and the instantaneous circumflu

8、ence is used to regulate the output current, each inverter has good transient performance and the parallel system has good current sharing performance. However, its analog signal communication is easy to be disturbed and the signal isolation is complicated, which decrease the reliability of the para

9、llel system. Independent control without interconnection droops the output voltage and frequency of inverters, the link among inverters is only via power lines. Thus fewer interconnections are needed and the reliability of inverter parallel systems is improved. Traditionally, this control strategy a

10、ssumes the output impedance of inverters is mainly inductive due to high inductive component of the line impedance and the large inductor filter. Thus active power-frequency droop and reactive power-voltage droop schemes are adopted. However, this is not always true as the closed-loop output impedan

11、ce also depends on the control strategy, and the line impedance is predominantly resistive for low voltage cabling. Thus, there is coupling relationship between output active/reactive power and frequency/amplitude of the output voltage. Traditional independence control may lead to instability of inv

12、erter parallel systems.In this paper, a decoupling control strategy for inverter parallel systems is proposed. The active power and reactive power of inverters in a parallel system are calculate by their corresponding output voltage and output current, and the output power information is shared by c

13、ontroller area network(CAN)bus communication. Then the active and reactive power circumfluence of each inverter is calculated and applied to regulate its corresponding output voltage and output frequency by decoupling of the power circumfluence, respectively. Thus, the proposed decoupling control st

14、rategy overcomes the disadvantages of inverter parallel systems controlled by independence control without intercommunication and instantaneous-current control. The inverter parallel system implemented by this strategy can achieve better current-sharing performance, good stability, and good reliabil

15、ity.2. Analysis of Single Phase PWM InverterDual closed-loop feedback control is usually adopted to control single phase inverters.Fig.1 shows a dual closed-loop feedback control scheme with an inductor-current inner loop and a capacitor voltage outer loop. The capacitor-voltage outer loop adopts pr

16、oportion-integral control to regulate output voltage, where andare proportional coefficient and integral coefficient, respectively. The inductor-current inner loop uses proportional control to enhance the transient response of the inverter, is a proportional coefficient. In Fig.1,the power stage inc

17、ludes a full-bridge configuration and an L-C filter, is DC link voltage, to are power switches, L and C are filter inductor and capacitor,is a sinusoidal reference voltage signal of the inverter,is the sum of inductor equivalent series resistance, switch on-resistance, and connection-line resistance

18、. According to nonlinear control and feedback linearization theory, open-loop averaged output voltage can be characterized by (1)where means the average value of x over one switching cycle and u is the control variable, which can take the values 1,0,or-1,depending on the state of switches ,and.For t

19、he dual closed-loop feedback control inverter shown in Fig.1,the controller can be characterized by (2)From (1) and (2) ,the dynamic characteristics of the closed-loop output voltage can be expressed in Laplace domain as (3)The single phase dual closed-loop inverter can be modeled by two terminal eq

20、uivalent circuits as (4) (5) (6)Fig.1.Block diagram of Single phase dual closed-loop inverter.Frequency (rad/sec)(a)Frequency (rad/sec)(b)Fig.2.Bode diagram of the voltage gain and the equivalent outputimpedance of the dual closed-loop inverter:(a)magnitude vs.frequency and(b)phase vs.frequency.Fig.

21、3.Inverter equivalent circuit.where is the voltage gain andis the equivalent output impedance. The bode diagram ofandare shown in Fig.2. From (6), we can know that the equivalent output impedance is closely related to the parameters of the output filter and the feedback control parameters. Let R be

22、the resistive component and X the inductive component of equivalent impedance Z(s).The inverter equivalent circuit can be shown as Fig.3.When, , and,the relations between the impedance ratio and the control parameters, andare shown in Fig.4.Fig.4.Relations between the impedance ratio R/X and control

23、 parameters:(a)R/X vs.,(b)R/X vs.,and(c)R/X vs.From Fig.4, the equivalent output impedance trends to be resistive when PI control parameterandare increasing, and trends to be inductive when PI control parameteris increasing. In the design of dual closed-loop single phase inverter, the PI control par

24、ameters must be chosen carefully as they affect both the transient characteristics of the inverter and the current sharing performance of the inverter parallel system.3. Analysis of Inverter Parallel SystemBased on above discussion, the equivalent circuit of inverter parallel system of two inverter

25、modular can be given as Fig.5, whereis load voltage, andare the output voltage and equivalent output impedance of inverter 1,andare the output voltage and equivalent output impedance of inverter 2.In the inverter parallel system, the active output power and the reactive output power of the inverter

26、1 can be expressed as: (7)Due to small difference the phase of output voltage between individual inverters, we can assume that,and.Therefore, we have (8)Similarly for the inverter 2, we have (9)Fig.5.The equivalent circuit of the parallel system of two inverter modular.Fig.6.Structure of parallel op

27、eration system.From above analysis we can know that the active/reactive power is related to the amplitude and phase of voltage, and the influence of output voltage amplitude and phase on active and reactive power is closely related to the inductive component and resistive component of the output imp

28、edance of the inverter. When resistive component is dominating, active power is mainly depended on the amplitude of output voltage, and reactive power is mainly depended on the phase of the output voltage, and vice versa.4. Control DesignFig.6 shows the structure of inverter parallel system. The dig

29、ital signal processor TMS320F2812 is adopted in the proposed parallel system; the inverters decouple the active power and the reactive power circumfluence to regulate the amplitude and the phase of the sinusoidal reference voltage signal. Each inverter adopts instantaneous voltage and instantaneous

30、current dual closed-loop feedback control. The inverters can operate not only independently but also in parallel. The CAN bus transfers information of the active power and the reactive power among the inverters.Fig.7.Decoupling control strategy.Fig.8.Experiment wave of inverter parallel system: (a)s

31、teady current wave,(b)current wave with a sudden increasing load, and (c)current wave with a sudden decreasing load.In the parallel operation system, the differences between the output active power and reactive power of individual inverter lead to the asymmetry of output current among the inverters.

32、 The relation between the active/reactive power and output voltage amplitude/phase is given by (8).In the single phase SPWM inverter which adopts dual closed-loop feedback control, output voltage tracks the amplitude and phase of the sinusoidal reference voltage signal. Thus, the output active and r

33、eactive power of the inverter can be controlled by the amplitude and phase of the reference voltage signal. If output active and reactive power equal to each other in the parallel system, the inverters can share the load current well. In the inverter, the output voltage and output current are sample

34、d by digital signal processor (DSP) for the calculation of output active and reactive power. All of the inverters share the active and reactive power by the CAN bus, each inverter calculates its corresponding active power circumfluenceand reactive power circumfluence.These circumfluence signals are

35、decoupled to regulate the amplitude and the phase of reference voltage signal as shown in Fig.7.Therefore, each inverter outputs the same active power and reactive power, and the inverters can share the load current in the system.5. Experiment ResultsTwo 2 KVA inverters are used in our experiment. I

36、n the parallel system, the output filter inductance is 500H,the filter capacitance is 10F,the DC input voltage is 200 V DC, and the AC output voltage is 110 V with 50 Hz. 6N137 is used to isolate the signal between the inverters and the CAN bus, the baud rate of CAN bus is set to 1 Mbps. The closed-

37、loop control, decoupling arithmetic and the SPWM control signal are realized by TMS320F2812 digital signal processor. Experiment results of the inverter parallel system are shown in Fig.8.In the steady state, the two inverters share the current very well and during transient under sudden load variat

38、ion, the inverter parallel system still can work well. This indicates that excellent load sharing is achieved between these two inverters.6. ConclusionsThis paper proposes a decoupling control strategy for inverter parallel systems. Theoretical analysis and experimental results verify the feasibilit

39、y of the proposed control strategy. This control strategy has the following characteristics:1)inverters can work independently or in parallel;2)CAN bus is used for the inverter parallel system; 3)the inverter parallel system supports hot-swappable operation and has good reliability and expansibility

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49、SPWM逆變器并聯(lián)解耦控制策略徐順剛，徐建平，曹太強(qiáng)摘要：基于單相電壓源的SPWM（正弦脈寬調(diào)制）逆變器的等效輸出阻抗，逆變器并聯(lián)系統(tǒng)的解耦控制策略被提出。通過計(jì)算輸出電壓和電流計(jì)算出逆變器的有功功率和無功功率，并通過控制器區(qū)域網(wǎng)絡(luò)（CAN）總線發(fā)送到并行系統(tǒng)的其他逆變器。通過計(jì)算和解耦有功功率和無功功率環(huán)流，逆變器可以通過調(diào)節(jié)參考相位和幅度承受負(fù)載電流。實(shí)驗(yàn)結(jié)果表明一個(gè)110V/2kVA逆變器并聯(lián)系統(tǒng)的解耦控制策略是可行的。索引-CAN總線，電流共享，逆變器，并聯(lián)運(yùn)行。1. 簡介逆變器并聯(lián)運(yùn)行是一種有效提高逆變器系統(tǒng)的容量和可靠性的方式。并聯(lián)運(yùn)行的關(guān)鍵問題是負(fù)載電流的分布。在逆變器并聯(lián)系統(tǒng)中

50、，所有逆變器輸出電壓的幅值和相位應(yīng)嚴(yán)格相等，以保證每個(gè)逆變器有相同的負(fù)載電流。否則，逆變器并聯(lián)系統(tǒng)中的一些逆變器可能存在電流回流和超載。電流回流可能也降低了逆變器并聯(lián)系統(tǒng)的效率和可靠性。有各種技術(shù)可以控制逆變器的并聯(lián)運(yùn)行。在這些技術(shù)中，中央控制和主從控制比較容易實(shí)現(xiàn)，而且具有良好的電流共享性能。然而，這兩種控制策略因?yàn)槟孀兤髦g的配合操作降低了系統(tǒng)的可靠性。 在瞬時(shí)電流控制逆變器并聯(lián)系統(tǒng)，存在一條電流總線用來共享逆變器之間的電流信號(hào)，同時(shí)，瞬時(shí)回流用于調(diào)節(jié)輸出電流，每個(gè)逆變器具有良好的瞬態(tài)性能而且并行系統(tǒng)具有良好的電流共享性能。然而，其模擬信號(hào)通信容易受到干擾而且信號(hào)隔離難以實(shí)現(xiàn)，這降低了并聯(lián)

51、系統(tǒng)的可靠性。 沒有聯(lián)網(wǎng)的獨(dú)立控制拉低了逆變器輸出電壓和頻率，逆變器之間的聯(lián)系只能通過電源線。因此需要更少的互連，提高了逆變器并聯(lián)系統(tǒng)的可靠性。傳統(tǒng)上，這種控制策略假定逆變器輸出阻抗主要是由于高線路阻抗和大電感濾波電感元件電感。因此采用有功功率頻率衰減和無功功率電壓下降策略。然而，這并不總是真正閉環(huán)輸出阻抗也取決于控制策略和線路阻抗主要是低壓電纜的電阻。因此，輸出有功/無功功率和頻率/輸出電壓幅值之間有耦合關(guān)系。傳統(tǒng)的獨(dú)立控制可能會(huì)導(dǎo)致逆變器并聯(lián)系統(tǒng)的不穩(wěn)定。 在本文中，采用了逆變器并聯(lián)系統(tǒng)的解耦控制策略。逆變器的有功功率和無功功率在并行系統(tǒng)中通過相應(yīng)的輸出電壓和輸出電流計(jì)算得出，輸出功率信息

52、通過控制器區(qū)域網(wǎng)絡(luò)（CAN）總線通信共享。然后，分別計(jì)算每個(gè)逆變器的有功和無功回流，通過電源回流解耦來調(diào)節(jié)相應(yīng)的輸出電壓和輸出頻率。因此，提出的的解耦控制策略克服了獨(dú)立控制的逆變器并聯(lián)控制系統(tǒng)不互通和瞬時(shí)電流控制的缺點(diǎn)。運(yùn)用這一策略的逆變器并聯(lián)系統(tǒng)可以更好地實(shí)現(xiàn)電流共享性能，穩(wěn)定性好，可靠性高2. 單相PWM逆變器的分析通常采用雙閉環(huán)反饋控制策略來控制單相逆變器。圖1顯示了一個(gè)電感電流內(nèi)環(huán)和一個(gè)電容器的電壓外環(huán)的雙閉環(huán)反饋控制系統(tǒng)。電容電壓外環(huán)采用比例積分控制來調(diào)節(jié)輸出電壓，其中，和分別是比例系數(shù)和積分系數(shù)。電感電流內(nèi)環(huán)采用比例控制，以提高逆變器的瞬態(tài)響應(yīng)，是一個(gè)比例系數(shù)。功率級(jí)包括全橋配置電

53、路和LC濾波器，時(shí)直流母線電壓，到是四個(gè)電源開關(guān)，L和C是濾波電感和電容，是正弦逆變器的參考電壓信號(hào)，是電感的等效串聯(lián)電阻，切換電阻，連接線電阻的總和。根據(jù)非線性控制和反饋線性化理論，開環(huán)平均輸出電壓可表征為 (1)其中，是一個(gè)開關(guān)周期中x的平均值，u是控制變量，可以根據(jù)開關(guān),和的狀態(tài)取值為1,0或者-1。在圖1所示的雙閉環(huán)反饋控制逆變器中，控制器可以表征為 (2)由（1）和（2）知，閉環(huán)輸出電壓的動(dòng)態(tài)特性經(jīng)拉普拉斯變換可表示為 (3)可以通過兩個(gè)終端等效電路對(duì)單相雙閉環(huán)逆變器建模 (4) (5) (6)圖1 單相雙閉環(huán)逆變器的結(jié)構(gòu)框圖頻率（弧度/秒）（a）頻率（弧度/秒）（b）圖2 Bode

54、圖和等效輸出電壓增益阻抗的雙閉環(huán)變頻器：（a） 幅度與頻率（b）相位與頻率圖3 逆變器等效電路其中，表示電壓增益，表示等效輸出阻抗。和的波德圖如圖2所示。從公式（6）我們可以知道，等效輸出阻抗輸出濾波器和反饋控制參數(shù)的參數(shù)密切相關(guān)。令R是電阻元間件，X是等效阻抗為Z(s)的電感元件。逆變器等效電路如圖3所示。其中，, ，；阻抗比和控制參數(shù),和之間的關(guān)系如圖4所示。圖4阻抗比R/ X和控制參數(shù)之間的關(guān)系：（a）與（B）與（c）與由圖4可知，隨著PI控制參數(shù)和的增加，等效輸出阻抗是增加的，隨著PI控制參數(shù)的增加，等效輸出阻抗隨之減小。在設(shè)計(jì)雙閉環(huán)單相逆變器時(shí)，PI控制參數(shù)必須慎重選擇，因?yàn)樗鼈冇绊?/p>

55、將會(huì)逆變器的瞬態(tài)特性和逆變器并聯(lián)系統(tǒng)的電流共享性能。3逆變器并聯(lián)系統(tǒng)的分析基于上述討論，雙逆變器的模塊化逆變器并聯(lián)系統(tǒng)的等效電路如圖5所示，其中，是負(fù)載電壓，和表示輸出電壓和逆變器1的等效輸出阻抗，和表示輸出電壓和逆變器1的等效輸出阻抗。在逆變器并聯(lián)系統(tǒng)中，逆變器1的有功輸出功率和無功輸出功率可以表示為： (7)由于獨(dú)立逆變器輸出電壓的相位上的微小的差異，我們可以假設(shè),，因此，我們得到 (8)對(duì)逆變器2進(jìn)行類似處理，我們得到 (9)圖5 兩個(gè)逆變器的模塊化并聯(lián)系統(tǒng)的等效電路圖6 并聯(lián)運(yùn)行系統(tǒng)的結(jié)構(gòu)從以上分析我們可以知道，有功/無功功率與電壓的振幅和相位的有關(guān)，輸出電壓的幅值和相位及有功和無功功

56、率與感應(yīng)組件和逆變器的輸出阻抗的電阻分量密切相關(guān)。當(dāng)電阻元件起主導(dǎo)作用時(shí)，有功功率主要取決于輸出電壓的幅度，無功功率主要取決于輸出電壓的相位，反之亦然。4控制系統(tǒng)設(shè)計(jì)圖6為逆變器并聯(lián)系統(tǒng)的結(jié)構(gòu)。并行系統(tǒng)采用數(shù)字信號(hào)處理器TMS320F2812，逆變器解耦有功功率和的無功功率回流來調(diào)節(jié)正弦參考電壓信號(hào)的振幅和相位。每個(gè)逆變器采用瞬時(shí)電壓及瞬間電流雙閉環(huán)反饋控制。逆變器不僅可以獨(dú)立操作而且可以平行運(yùn)行。 CAN總線傳輸逆變器之間的有功功率和無功功率的信息。圖7 解耦控制策略圖8逆變器并聯(lián)系統(tǒng)的實(shí)驗(yàn)波形：（a）穩(wěn)定的電流波，（b）突然增加負(fù)荷的電流波形（c）突然降低負(fù)荷的電流波形。在并聯(lián)運(yùn)行系統(tǒng)，單個(gè)逆變器輸出有功功率和無功之間的差異，導(dǎo)致