外文翻译---单相SPWM逆变器并联解耦控制策略.docx

附录6 外文文献Decoupling Control Strategy for Single Phase SPWM Parallel InvertersShun-Gang Xu,Jian-Ping Xu,and Tai-Qiang Cao1. 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 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. 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 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 circumfluence 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 parallel 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 assumes 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 impedance 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 inverter 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 controller 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 strategy 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 reliability.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 proportion-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 includes 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. 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 the 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 equivalent 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.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 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 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 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 SystemBased on above discussion, the equivalent circuit of inverter parallel system of two inverter 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 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 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 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 shows 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 inverter 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.8.Experiment wave of inverter parallel system: (a)steady 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. 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 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, the output voltage and output current are sampled 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 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. In 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-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 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 analysis 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-swappable operation and has good reliability and expansibility.中文译文：单相SPWM逆变器并联解耦控制策略徐顺刚，徐建平，曹太强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的电流共享性能。然而，其模拟信号通信容易受到干扰而且信号隔离难以实现，这降低了并联系统的可靠性。 没有联网的独立控制拉低了逆变器输出电压和频率，逆变器之间的联系只能通过电源线。因此需要更少的互连，提高了逆变器并联系统的可靠性。传统上，这种控制策略假定逆变器输出阻抗主要是由于高线路阻抗和大电感滤波电感元件电感。因此采用有功功率频率衰减和无功功率电压下降策略。然而，这并不总是真正闭环输出阻抗也取决于控制策略和线路阻抗主要是低压电缆的电阻。因此，输出有功/无功功率和频率/输出电压幅值之间有耦合关系。传统的独立控制可能会导致逆变器并联系统的不稳定。 在本文中，采用了逆变器并联系统的解耦控制策略。逆变器的有功功率和无功功率在并行系统中通过相应的输出电压和输出电流计算得出，输出功率信息通过控制器区域网络（CAN）总线通信共享。然后，分别计算每个逆变器的有功和无功回流，通过电源回流解耦来调节相应的输出电压和输出频率。因此，提出的的解耦控制策略克服了独立控制的逆变器并联控制系统不互通和瞬时电流控制的缺点。运用这一策略的逆变器并联系统可以更好地实现电流共享性能，稳定性好，可靠性高单相PWM逆变器的分析通常采用双闭环反馈控制策略来控制单相逆变器。图1显示了一个电感电流内环和一个电容器的电压外环的双闭环反馈控制系统。电容电压外环采用比例积分控制来调节输出电压，其中，和分别是比例系数和积分系数。电感电流内环采用比例控制，以提高逆变器的瞬态响应，是一个比例系数。功率级包括全桥配置电路和LC滤波器，时直流母线电压，到是四个电源开关，L和C是滤波电感和电容，是正弦逆变器的参考电压信号，是电感的等效串联电阻，切换电阻，连接线电阻的总和。根据非线性控制和反馈线性化理论，开环平均输出电压可表征为 (1)其中，是一个开关周期中x的平均值，u是控制变量，可以根据开关,和的状态取值为1,0或者-1。在图1所示的双闭环反馈控制逆变器中，控制器可以表征为 (2)由（1）和（2）知，闭环输出电压的动态特性经拉普拉斯变换可表示为 (3)可以通过两个终端等效电路对单相双闭环逆变器建模 (4) (5) (6)图1 单相双闭环逆变器的结构框图频率（弧度/秒）（a）频率（弧度/秒）（b）图2 Bode图和等效输出电压增益阻抗的双闭环变频器：幅度与频率（b）相位与频率图3 逆变器等效电路其中，表示电压增益，表示等效输出阻抗。和的波德图如图2所示。从公式（6）我们可以知道，等效输出阻抗输出滤波器和反馈控制参数的参数密切相关。令R是电阻元间件，X是等效阻抗为Z(s)的电感元件。逆变器等效电路如图3所示。其中，, ，；阻抗比和控制参数,和之间的关系如图4所示。图4阻抗比R/ X和控制参数之间的关系：（a）与（B）与（c）与由图4可知，随着PI控制参数和的增加，等效输出阻抗是增加的，随着PI控制参数的增加，等效输出阻抗随之减小。在设计