单相SPWM逆变器并联解耦控制策略.doc

1、英文资料原文来源 : 出自 JOURNAL OF ELECTRONIC SCIENCE ANDTECHNOLOGY OF CHINA,VOL.7,NO.3, SEPTEMBER 2009Decoupling Control Strategy for Single Phase SPWM ParallelInvertersShun-Gang Xu,Jian-Ping Xu,and Tai-Qiang CaoAbstract: A decoupling control strategy of inverter parallel system is proposed based on the equi

2、valent 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 network(CAN)

3、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 decoupling contro

4、l 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 an inverter p

5、arallel 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. The current c

6、ircumfluence 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 performance.

7、 However, these two control strategies work at the cost ofsystem 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 instantaneouscircumfluence is used to

8、 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 parallel system.Ind

9、ependent 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 assumes the outpu

10、t 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 impedance also depends

11、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 inverter parallel s

12、ystems.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 controller area n

13、etwork(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 strategy overcomes

14、 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 reliability.2. Analysis

15、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 proportion-integra

16、l control to regulate output voltage, where kPv andkIv are proportionalcoefficient and integral coefficient, respectively. The inductor-current inner loop uses proportional control to enhance the transient response of the inverter, kPi is a proportional coefficient.In Fig.1,the power stage includes

17、a full-bridge configuration and an L-C filter,Vinis DClink voltage,s1 tos4 are power switches, L and C are filter inductor and capacitor,vref is asinusoidal reference voltage signal of the inverter, rL is the sum of inductor equivalentseries resistance, switch on-resistance, and connection-line resi

18、stance. According to nonlinear control and feedback linearization theory, open-loop averaged output voltage can be characterized byLC d 2 v0rL C d v0v0L d i0rL i0Vin u(1)dt 2dtdtwhere x means the average value of x over one switching cycle and u is the control variable, which can take the values 1,0

19、,or-1,depending on the state of switches S1 , S2 , S3 andS4 .For the dual closed-loop feedback control inverter shown in Fig.1,thecontroller can be characterized byVin ukPv s kIv vrefv0i0 Cs v0 kPi(2)sFrom (1) and (2) ,the dynamic characteristics of the closed-loop output voltage can be expressed in

20、 Laplace domain asv0kPv kPi skPi kIvvrefLCs3rLC kPi C s21 kPvkPis kPi kIvLs2rLkPis(3)i0LCs3rLC kPi Cs21kPv kPi skPi kIvThe single phase dual closed-loop inverter can be modeled by two terminal equivalentcircuits asv0G (s)vrefZ ( s)i0(4)G (s)kPv kPi skPi kIv(5)3rLCkPi Cs21kPv kPisLCskPi kIvZ ( s)Ls2r

21、LkPis(6)rLCkPi Cs21kPv kPisLCs3kPi kIvFig.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.frequenc

22、y.Fig.3.Inverter equivalent circuit.where G (s) is the voltage gain andZ(s) is the equivalent output impedance. The bodediagram of G(s) andZ (s) are shown in Fig.2.From (6), we can know that the equivalent output impedance is closely related to theparameters of the output filter and the feedback con

23、trol parameters. Let R be the resistivecomponent and X the inductive component of equivalent impedance Z(s).The inverter equivalent circuit can be shown as Fig.3.When L 500 H , C 10 F , andrL 0.1 ,therelations between the impedance ratio R Xand the control parameterskPv , kPi , andkIv areshown in Fi

24、g.4.Fig.4.Relations between the impedance ratio R/X and control parameters:(a)R/X vs. kPv ,(b)R/X vs. kPi ,and(c)R/X vs. kIv .From Fig.4, the equivalent output impedance trends to be resistive when PI control parameter kPv and kPi are increasing, and trends to be inductive when PI controlparameterkI

25、v is increasing. In the design of dual closed-loop single phase inverter, the PIcontrol parameters 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 SystemBas

26、ed on above discussion, the equivalent circuit of inverter parallel system of two inverter modular can be given as Fig.5, where E 0 is load voltage,E1 1 G1 (s)vref 1 and R1jX 1Z1 (s) are the outputvoltage and equivalent outputimpedance of inverter 1, E22G2 ( s)vref 2 andR2 jX 2Z2 ( s) are the output

27、 voltage andequivalent output impedance of inverter 2.In the inverter parallel system, the active output power and the reactive output power of the inverter 1 can be expressed as:E0R1E1 cos 1R1E0 X1 E1 sin 1P1R12X12E0X1E1 cos 1(7)R1E1 sin 1 X1E0Q1R12X12Due to small difference the phase of output vol

28、tage between individual inverters, we canassume thatsin ii ,cos i1, R1R2R and X1X 2X .Therefore, we haveRE1 E0E1E0 X 1 RE02PR2X 21XE1E0E1 E0R 1RE02(8)Q1R2X 2Similarly for the inverter 2, we haveRE2 E0E2E0 X 2RE02P2R2X 2(9)2XEEE E RRE022200Q2R2X 2Fig.5.The equivalent circuit of the parallel system of

29、 two inverter modular.Fig.6.Structure of parallel operation 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

30、 component and resistive component of the output impedance 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 show

31、s the structure of inverter parallel system. The digital 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 inve

32、rter adopts instantaneous voltage and instantaneous 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

33、.8.Experiment wave of inverter parallel system: (a)steady current wave,(b)current wave with asudden 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 t

34、he asymmetry of output current among the inverters. 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 refe

35、rence voltage signal. Thus, the output active and reactive 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

36、, the output voltage and output current are sampled by digital signalprocessor (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 circumfluence P and reactive

37、power circumfluence Q .Thesecircumfluence signals are 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 Re

38、sultsTwo 2 KVA inverters are used in our experiment. In the parallel system, the output filterinductance is 500 H,thefilter capacitance is 10 F,the DC input voltage DC,is200andV 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

39、baud rate of CAN bus is set to 1 Mbps. The closed-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

40、well and during transient under sudden load variation, 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 analy

41、sis and experimental results verify the feasibility 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-s operation

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51、M逆变器并联解耦控制策略徐顺刚，徐建平，曹太强摘要： 基于单相电压源的SPWM （正弦脉宽调制）逆变器的等效输出阻抗，逆变器并联系统的解耦控制策略被提出。 通过计算输出电压和电流计算出逆变器的有功功率和无功功率，并通过控制器区域网络（CAN ）总线发送到并行系统的其他逆变器。通过计算和解耦有功功率和无功功率环流，逆变器可以通过调节参考相位和幅度承受负载电流。实验结果表明一个110V/2kVA 逆变器并联系统的解耦控制策略是可行的。索引 -CAN总线，电流共享，逆变器，并联运行。1. 简介逆变器并联运行是一种有效提高逆变器系统的容量和可靠性的方式。 并联运行的关键问题是负载电流的分布。 在逆变器并联系统中， 所有逆变器输出电压的幅值和相位应严格相等， 以保证每个逆变器有相同的负载电流。 否则，逆变器并联系统中的一些逆变器可能存在电流回流和超载。 电流回流可能也降低了逆变器并联系统的效率和可靠性。有各种技术可以控制逆变器的并联运行。 在这些技术中， 中央控制和主从控制比较容易实现， 而且具有良好的电流共享性能。 然而，这两种控制策略因为逆变器之间的配合操作降低了系统的可靠性。在瞬时电流控制逆变器并联系统， 存在一条电流总线用来共享逆变器之间的电流信号，同时，瞬时回流用于调节输出电流， 每个逆变器具有良好的瞬态性能而且并行系统具有良好