【作者】 肖华锋；

【导师】 谢少军；

【作者基本信息】 南京航空航天大学 ， 电力电子与电力传动， 2010， 博士

【摘要】 近年来,光伏并网发电系统在发达国家得到大规模应用,但在发展中国家发展缓慢,其瓶颈在于其经济性较差。提高光伏发电系统的经济性,除了提高光电转换效率外,发展高效的逆变器结构和电能利用架构是可行的突破口。论文重点从高效率非隔离并网逆变器技术和分布式直流供电(直流微网)架构开展研究工作。非隔离型并网逆变器(TLGCI)结构不含变压器,拥有变换效率高,体积、重量和成本低等优势,论文致力于非隔离光伏并网逆变器相关技术研究。首先详细介绍两级式非隔离并网逆变器的设计过程,包括直流变换器和交流逆变器拓扑、最大功率点跟踪(MPPT)、直流母线电压控制和进网电流控制等环节的设计。出于系统分级优化和控制的方便,提出采用交错开关方式的双管Buck-Boost变换器为前级直流变换器,可以实现储能电感最小、有能量直接传输模态且控制电路简单,是一种高性价比的方案。通过并网逆变器样机性能测试和分析,得出高效率非隔离并网逆变器需要着力解决漏电流(LC)和低阻抗进网滤波器问题。光伏并网逆变器中变压器的消除使得电池板与电网之间有了电气连接,漏电流可能会大幅增加,带来安全隐患。论文建立了较完善的非隔离单相并网逆变器共模分析模型,总结出两条消除开关频率共模电压的途径,并将其应用到两大类并网逆变器拓扑,即全桥类和半桥类光伏并网逆变器结构中。在H5全桥逆变器结构中加入一支可控开关管和分压电容构成双向箝位支路,可以实现续流阶段时续流回路电位处于电池电压一半的固定电压,并保证了功率传输阶段输出电流仅流经3支开关管,有效降低了导通损耗。另外,箝位支路的加入使得电池侧正端引入的高频开关管和箝位开关管的电压应力仅为输入电池电压的一半,有利于效率的进一步提高。论文从逆变器效率和漏电流抑制效果两方面比较了几种专利拓扑和本文提出的电路拓扑(简称oH5),论证了所提出拓扑是一种优化结构。在半桥类逆变器结构中,由于电容桥臂和开关管桥臂中点寄生电容的不同使得原有拓扑结构的漏电流抑制效果并不理想,论文提出了“滤波支路抵消法”、“寄生支路抵消法”和“全抵消法”三种可能的补偿措施,并从可实现性和实际测试效果两个方面说明了“全抵消法”的优越性。高可靠性同样是非隔离光伏并网逆变器的重要要求。然而,非隔离型桥式逆变器的桥臂同样存在直通的危险。论文通过引入双降压式半桥逆变器(DBHBI)防桥臂直通结构增强了桥式并网逆变器的可靠性,提出一种新型的分裂电感中点箝位三电平逆变器(SI– NPCTLI),并将其推广至三相系统中。同样地,在oH5拓扑中引入DBHBI结构实现了提高可靠性的目的。三阶LCL进网滤波器具有阻抗小和谐波抑制能力强等优势,结合非隔离光伏并网逆变器拓扑可以实现高效率和高性能。论文在综合了现有文献关于LCL滤波器设计方法的基础上采用“折中”的思想提出一种滤波器参数设计流程,兼顾工程经验和理论优化。针对现有文献关于LCL滤波器有源阻尼(AD)方法研究不完善的现状,开展采用状态变量反馈增加控制对象阻尼方法的系统化研究。提出一种新型的采用网侧电感电压微分反馈的有源阻尼方法,并结合进网电流采用准谐振控制器详细讨论了逆变器控制结构和参数的设计过程。论文最后在光伏等可持续能源高效利用架构方面做了部分前期探索,介绍一种基于直流供电的分布式发电系统——直流微网。在详细介绍系统架构和关键技术后重点讨论了系统组成所需的四种基本接口电路的拓扑选择:直流微网与大电网接口电路选择带隔离变压器的多台单相双向AC/DC变换器,可以优化效率,降低待机损耗;直流微网与储能设备接口电路选用三通道非隔离双向DC/DC变换器,配置超级电容为储能设备,可以实现动态功率的快速平衡,大幅提高供电品质;在直流微网双供电母线接口电路中,提出低压蓄电池侧采用电流源型半桥拓扑和高压侧选用电压源型半桥拓扑,组成电流源型半桥-电压源型半桥完全对偶、对称的组合式结构。并在电流源侧加入有源箝位网络实现开关管的零电压开通(ZVS)和消除电压尖峰;提出对两个半桥产生的方波电压进行相移角控制和对电流源半桥的主开关管占空比实行PWM控制以实现端电压波动时变压器两端电压匹配,从而有效降低环流损耗和实现全范围ZVS。在直流微网的光伏接口电路中,针对双管Buck-Boost变换器的电路结构提出增加一个附加绕组和两只辅助二极管实现原续流二极管的零电流关断和辅助二极管的关断电流下降率可控,大幅降低了变换器的开关损耗。上述接口变换器的开发为直流微网实验演示平台构建、进一步研究可持续能源发电的高效利用技术打下了一定的基础。更多还原

【Abstract】 At present, the barrier to the large-scale application of Photovoltaic grid-connected generator is its economic performances in developing countries. In addition to improving the photo-electric transformation efficiency, it is one of the most feasible schemes to develop the high efficiency inverter topology and utilization scheme of electric energy. This thesis is meant to research on the high effieciency transformerless grid-connected inverters (TLGCIs) and the distributed DC supply system (DC-Microgrid).TLGCIs are characterized with higher efficiency, lower bulk, weight and cost, etc., its technology issues have been discussed in this thesis. Firstly, the design process of two-stage TLGCI, including the topologies of DC converter and grid-connected inverter, maximum power point tracking (MPPT), DC bus voltage controller, grid current controller, has been presented. For the convenience of system optimized and control, the double switch Buck-Boost converer with interleaving switching strategy is proposed as pre-stage DC converter. Characterized with lowest inductance, transferring power directly in partial, and simple control, this converer has achieved high performance with low cost. Through TLGCI prototype testing and analyzing, it showed that the leakage current and low impedance filter are keys in TLGCIs for PV application.While no transformer is used in TLGCI, the galvanic connection appears between the PV arrays and the grid. When energized by a fluctuating potential, the stray capacitance to the earth formed by the surface of the PV array may lead to the occurrence of leakage currents. A full-scale leakage current analytical model for TLGCI and the rules to eliminat common-mode source at switching frequency have been developed, and the rules have been adopted in full-bridge and half-bridge TLGCI respectively. An optimized full-bridge structure with two additional switches and capacitor divider is proposed in this thesis, which guarantees that freewheeling path is clamped to half input voltage in freewheeling period, and, the high frequency common-mode voltage has been avoided in unipolar SPWM full-bridge inverter and the output current flows through only three switches in power processing period. In addition, the clamping branch makes the voltage stress of the added switches be equal to half input voltage. The total losses of power devices in several existing topologies and proposed topology (named as oH5) are fairly calculated. Finally, the common-mode performance of these topologies is compared by a universal prototype inverter rated at 1kW. In half-bridge TLGCI, the leakage current suppressing performance of conventional topology structure is not perfect due to the different construction mechanism of parasitic parameters of bridge legs. Some feasible compensation strategies, named as‘Filter branch offset solution’,‘Parasitic branch offset solution’and‘Full-offset solution’, have been proposed. The compensation effectiveness of these strategies is verified by theoretic analysis and circuit test.The high reliability is an important index of TLGCI. Unfortunately, the bridge-type TLGCI also suffer from the shoot-through problem, which is a major killer of the reliability. Based on neutral point clamped three level inverter (NPCTLI) and dual Buck half bridge inverter (DBHBI), a novel Split-Inductor-Neutral-Point -Clamped three level inverter (SI-NPCTLI) with variable hysteresis band fixed-frequency control is proposed in this thesis. There are no leakage current and shoot-through problems in the proposed inverter. With the above control method, single-phase SI-NPCTLI can be extended to three-phase four-line grid-connected inverter structure. Similarly, the oH5 has been improved with above methodology.Third-order LCL filter characterized with low impedance and high harmonic attenuation performance, is suitable for TLGCI in PV applications. Base on the literatures about LCL filter design, a design program for LCL filter has been presented with trade-off means. In order to enhance the damping capability of the LCL filter, the state variable feedback to advance damping capability has been analyzed systemically. A novel damping method with differential feedback of grid-side inductor voltage has been proposed, and a parameter design procedure with proposed damping strategy and proportional plus resonant (PR) controller has been discussed detailedly.Finally, the thesis pushed primary research on high efficiency utilization framework of surtainable energy resource, a distributed generation system with DC-bus, namely DC-Microgrid, has been introduced. Following the introduction of system framework and key techniques, four converter topologies have been discussed in detail. multi-single-phase bi-directional AC/DC converter with line-transformer has been employed to connect DC-bus to the grid; a three channels transformerless bi-directional DC/DC converter has been adopted to connect DC-bus to energy storage equipment; For transferring energy between the two DC buses, a current-voltage-fed bidirectional DC-DC converter has been proposed, which refers to a current-fed inverter at low voltage side and a voltage-fed inverter at high voltage side, can realize ZVS for the switches with the use of phase-shift (PS) technology. In order to avoid the current-fed switches suffer from high voltage spike and high circulating conduction loss, a novel ZVS bidirectional DC-DC converter with phase-shift plus PWM (PSP) control scheme is proposed in this thesis, Thanks to the active clamping branch and PSP technology, the converter can realize ZVS for all switches in a wide range of load variation while input or output voltage varies; A improved double switch Buck-Boost converter with an auxiliary winding and two diode has been as interface to connect PV array with DC-bus. Above interface converters lay a solid foundation for DC-Microgrid investigation.更多还原