1、附录 6 外文文献 Decoupling Control Strategyfor Single Phase SPWM Parallel Inverters Shun-Gang Xu,Jian-Ping Xu,and Tai-Qiang Cao 1. Introduction Parallel operation of inverters is an efficient way toenhance the capacity and reliability of inverter systems.The key issue of parallel operation is the distribu
2、tion of theload current.In an inverter parallel system,the amplitudesand phases of output voltages of all inverters should strictlyequal to each other to guarantee that each inverter sharesthe same load current.Otherwise,the current circumfluenceand overload of some inverters in the inverter paralle
3、lsystem may exist.The current circumfluence may alsodecrease the efficiency and reliability of the inverterparallel system. There are various techniques for the control of inverterparallel operation.Among these techniques,central controland master-slave control are easy to implement and havegood cur
4、rent-sharing performance.However,these twocontrol strategies work at the cost of system reliabilitybecause of conjunction operation among inverters. In instantaneous-current controlof inverter parallelsystem,there is a current bus to share the current signalamong inverters and the instantaneous circ
5、umfluence isused to regulate the output current,each inverter has goodtransient performance and the parallel system has goodcurrent sharing performance.However,its analog signalcommunication is easy to be disturbed and the signalisolation is complicated,which decrease the reliability ofthe parallel
6、system. Independent control without interconnection droopstheoutput voltage and frequency of inverters,the link amonginverters is only via power lines.Thus fewerinterconnections are needed and the reliability of inverterparallel systems is improved.Traditionally,this controlstrategy assumes the outp
7、ut impedance of inverters ismainly inductive due to high inductive component of theline impedance and the large inductor filter.Thus activepower-frequency droop and reactive power-voltage droopschemes are adopted.However,this is not always true asthe closed-loop output impedance also depends on thec
8、ontrol strategy,and the line impedance is predominantlyresistive for low voltage cabling.Thus,there is couplingrelationship between output active/reactive power andfrequency/amplitude of the output voltage.Traditionalindependence control may lead to instability of inverterparallel systems. In this p
9、aper,adecoupling control strategy for inverterparallel systems is proposed.The active power and reactivepower of inverters in a parallel system are calculate by theircorresponding output voltage and output current,and theoutput power information is shared by controller areanetwork(CAN)bus communicat
10、ion.Then the active andreactive power circumfluence of each inverter is calculatedand applied to regulate its corresponding output voltage andoutput frequency by decoupling of the power circumfluence,respectively.Thus,the proposed decoupling controlstrategy overcomes the disadvantages of inverter pa
11、rallelsystems controlled by independence control withoutintercommunication and instantaneous-current control.Theinverter parallel system implemented by this strategy canachieve better current-sharing performance,good stability,and good reliability. 2.Analysis of Single Phase PWMInverter Dual closed-
12、loop feedback control is usually adopted tocontrol single phase inverters.Fig.1 shows a dualclosed-loop feedback control scheme with an inductor-current inner loop and a capacitor voltage outer loop.Thecapacitor-voltage outer loop adopts proportion-integralcontrol to regulate output voltage,where Pv
13、k andIvk areproportional coefficient and integral coefficient,respectively.The inductor-current inner loop uses proportional control toenhance the transient response of the inverter, Pik is aproportional coefficient. In Fig.1,the power stage includes a full-bridgeconfiguration and an L-C filter, inV
14、 is DC link voltage, 1s to 4s are power switches,L and C are filter inductor andcapacitor,refvis a sinusoidal reference voltage signal ofthe inverter, Lr is the sum of inductor equivalent seriesresistance,switch on-resistance,and connection-lineresistance.According to nonlinear control and feedbackl
15、inearization theory,open-loop averaged output voltage canbe characterized by 2 0 0 0002 L L i nd v d v d iL C r C v L r i V ud t d t d t (1) where xmeans the average value of x over oneswitchingcycle and u is the control variable,which cantake the values 1,0,or-1,depending on the state ofswitches 1S
16、 , 2S , 3Sand 4S .For the dual closed-loopfeedback control inverter shown in Fig.1,the controller canbe characterized by 0 0 0P v I vi n r e f P ik s kV u v v i C s v ks (2) From(1)and(2),the dynamic characteristics of theclosed-loop output voltage can be expressed in Laplacedomain as 0 32203211P v
17、P i P i I vr e fL P i P v P i P i I vL P iL P i P v P i P i I vk k s k kvvL C s r C k C s k k s k kL s r k s iL C s r C k C s k k s k k (3) The single phase dual closed-loop inverter can bemodeled by two terminal equivalent circuits as 00( ) ( )re fv G s v Z s i (4) 32() 1P v P i P i I vL P i P v P i P i I vk k s k kGs L C s r C k C s k k s k k (5) 232() 1L P iL P i P v P i P i I vL s r k sZsL C s r C k C s k k s k k (6)
