【作者】 蔡春伟；

【导师】 曲延滨；

【作者基本信息】 哈尔滨工业大学 ， 电力电子与电力传动， 2013， 博士

【摘要】 Z源逆变器是近几年提出的新型电路拓扑，因具有单级可实现升降压变换，逆变桥同桥臂可以直通等优点，在新能源领域得到了广泛的应用。但传统Z源逆变器应用于发电系统时，由于Z源网络本身升压能力有限，存在开关管电压应力大、输入电压范围要求过高等问题。针对上述问题，本文提出了一种高增益Z源逆变器拓扑，同时对调制策略、数学建模、直流侧控制策略及在光伏发电离网模式下的控制策略等方面进行了研究。为提高Z源网络的升压能力，提出了一类基于开关电感的高增益Z源逆变器拓扑族。通过研究开关电感在传统DC/DC电路中提高升压能力的机理，并结合Z源逆变器拓扑结构的特点，提出了一种串联型高增益Z源逆变器拓扑。通过调整Z源网络和逆变桥的位置，使之不但提高了升压能力，而且减小了电容电压应力，具有内在抑制启动冲击的能力。但该串联型高增益拓扑的输入电流是断续的，为了减小输入电流纹波，首先提出一种准开关电感型Z源拓扑，使其纹波电流减小一倍；随后采用级联技术将前级滤波电路变换为一级boost电路，与后级Z源逆变器串联，不但减小了输入电流纹波，而且进一步提高了升压能力，但仿真分析发现该拓扑Z源组件动态特性不一致，增加了建模和控制的难度。为提高Z源逆变器的整体升压能力，提出了基于SVPWM的最大恒定升压调制策略。以串联型高增益Z源逆变器为研究对象，分析了不同直通插入方式对开关管电流应力和Z源电感充放电频率的影响，以及在给定有效矢量条件下直通时间对逆变器的升压能力的影响规律，从提高综合性能角度出发，提出了一种基于SVPWM的最大恒定升压调制策略，给出了具体实施方法。该策略通过单桥臂直通实现升压，不但没有增加开关频率，还增加了Z源网络组件的充放电频率，有利于减小Z源网络组件体积。仿真和实验结果表明该策略能够有效提高Z源逆变器的整体升压能力，并且直通矢量与有效矢量交替变换有利于避免Z源二极管电流断续工作模式（DCM, Discontinuous ConductionMode）。为精确控制直流链电压，建立了串联型高增益Z源逆变器的交流小信号模型，利用小信号模型提出了直流链电压直接控制策略。综合考虑负载、Z源无功组件、直通占空比、调制比对逆变系统的影响，采用信号流图法建立了小信号数学模型，并利用时域和频域法分析以上各参数对系统的动态特性的影响，为Z源组件的优化设计提供指导。通过对直流链电压进一步分析，建立直流链电压小信号模型，依据该模型提出了直流链电压直接控制策略，构建了直流链电压外环和电感电流内环的双闭环控制器。仿真和实验结果表明直流链电压直接控制策略能够有效提高直流侧电压的控制精度及对输入扰动的响应速度，采用的软启动控制策略能够有效抑制逆变器的启动冲击。为降低光伏发电系统中开关器件的电压应力，对直流侧与交流侧协同控制的控制策略进行了研究。由于光伏电池在负载能力范围内输出电压波动缓慢，本文结合最大恒定调制策略作用下的直流链峰值电压与输入电压和输出交流电压的关系，提出了一种利用光伏电池输出电压前馈的直流链电压控制策略。该策略能够实时根据光伏输出电压调整直流链电压，充分利用了零矢量时间，有效降低了开关管电压应力。交流侧采用输出电压和电感电流双闭环控制器实时跟随直流链电压，保证了输出控制精度，提高了对负载扰动的抑制能力。更多还原

【Abstract】 Z-Source Inverter (ZSI) has been proposed as a novel power conversiontopology in recent years. Due to the brand new circuit topology providing thefunctionality of single stage buck-boost power conversion and shoot-through statein the same leg, ZSI is especially suitable for renewable recourse. However, thetraditional ZSI applied in power generating system has the following drawbacks: therequired input voltage range and the voltage stress of the active devices is toohigher due to the limited boost inversion ability. In view of the issues above, afamily of high gain ZSIs will be proposed in this dissertation，and the improvedZSI topologies, modulation method, mathematical model, the control strategy in dcside and control strategy of the photovoltaic (PV) generating system in islandingoperation mode will be investigated.To improve the capability of DC boost inversion, a family of high gain ZSIs isproposed based on switched-inductor. The proposed series high gain ZSI topology isderived from investigating the mechanism of traditional DC/DC voltage boostcircuit, which performance is improved by the switched-inductor. The positions ofthe inverter bridge and the Z-source network are changed, as result, the capacitorvoltage stress can be reduced significantly and the inrush-current can be limited.But its input current is discontinues. To solve this problem, firstly the quasi-switched-inductor ZSI is proposed which input current ripple is half of the previousone. Subsequently, the input LC filter is transformed as a boost conversion circuit,and then a novel continues topology is proposed by cascading the boost circuit withthe series high gain ZSI. This continues input current topology can not onlydecrease the input current ripple but also further improve the boost conversioncapability. Unfortunately, the simulation results show that the dynamiccharacteristics of Z-source network components are inconsistent and this mayincrease the difficulty of the modeling and control.In order to improve the AC inversion capability of ZSI, a novel maximumconstant boost control method based on SVPWM is proposed. Based on the serieshigh boost gain topology, the novel method is the result of analyzing differentinserting effect on the current stress of active component, charging frequency of Z-source impedance components, as well as investigating shoot-through acting timeeffect on the boost inversion capability. In addition, the implementation method isgiven. The maximum ac gain is obtained without any extra switching stateintroduced, and the volume of the Z source can be lessened as a result of increasing charge-discharge frequency. What is more, this novel method avoids the Z-sourcediodes discontinuous conduction mode (DCM) by the active state and shoot-throughstate alternating. The simulation and experiment results verify the merits of theimproved module strategy.In order to control the dc-link voltage accurately, the ac small-signal model ofthe series high boost gain Z-Source inverter is set up in current continuous mode,and the dc-link voltage direct control strategy is proposed based on the small-signalmodel. Firstly, the equivalent circuit is obtained by the output filter and loadconverted, then the signal-flow-graph is utilized to set up the model taking intoaccount of shoot through state, active and null state. The effects of differentparameters on system dynamic performance are analyzed in frequency-domain andtime-domain. Results of the analysis would provide some basis to optimize the Z-source network. Secondly, the dc-link voltage is further analyzed and the small-signal model is obtained by state space averaged method, then the dc-link voltagecontrol method is derived based on this model, and the double closed loop controlleris built, including voltage loop control and current loop control. The simulation andexperimental results show that the accuracy of the dc-link voltage control and theinput disturbance rejection capability is improved, and the inrush surge issuppressed effectively.In order to decrease the voltage stress of the switch in PV power system whileimprove the conversion efficiency of the whole inversion system at the same time,the control strategy coordinating dc-side with ac-side is studied. Analysis of theoutput characteristics of PV module shows that PV module output voltage changesslowly. The PV module output voltage feedforward dc-link voltage control isproposed according to the relationship between dc-link voltage and input voltageunder the maximum constant boost control. The dc-link voltage setpoint can beadjusted real-time according to the output voltage of PV module, so the zero statetime can be utilized sufficiently and the voltage stress of the active component canbe decreased. In the ac-side, the outer voltage loop and inner current loopcontrollers are designed based on pole-assignment theory, then output steady-stateerror can be avoid by the outer loop and the load disturbance can be suppressed bythe inner loop.更多还原