模块化非隔离光伏并网逆变器及发电系统研究
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摘要
可再生能源尤其是光伏发电系统初期投资大、发电成本高，故并网逆变器以及并网发系统效率的提高对于缩短成本回收周期，更快地创造经济效益具有重要意义。本文以模块化和高效率为核心，研究非隔离光伏并网逆变器及系统中的关键技术。
针对基于直流总线的模块化光伏并网发电系统，提出了一种改进的以直流总线电压作为信息载体的功率变换管理和控制方法，旨在实现能量最优利用和系统运行模式的平滑切换。将系统分为四种运行模式，分别是孤岛运行蓄电池放电、并网运行网侧接口变换器整流、并网运行网侧接口变换器逆变、孤岛运行光伏接口变换器输出恒压。分析了系统运行模式与系统功率流的关系，设计令直流总线电压决定系统运行模式和模式切换，而无需中央控制器，降低了系统成本，提高了系统可靠性。分别给出了光伏、网侧和储能接口变换器的控制方法，使得系统在极端条件下，如孤岛运行蓄电池满电荷状态仍能达到功率平衡。
研究非隔离并网逆变器共直流和交流母线并联运行，提出了功率电路拓扑并联工作及进网电流解耦的条件。深入分析了各种非隔离全桥拓扑形式和PWM（Pulse Width Modulation）调制方式的逆变器并联运行模态，指出双极性PWM逆变器并联运行时并联逆变器间的进网电流自然解耦；单极性倍频PWM逆变器并联运行时并联逆变器的进网电流存在高频耦合，但电流基波分量解耦；单极性PWM逆变器并联运行时并联逆变器间的电流存在高频耦合，导致电流基波分量耦合，不可并联运行。低漏电流的改进型全桥并网逆变器拓扑也可实现并联逆变器间的进网电流自然解耦。提出一种模块化光伏并网发电系统欧洲效率优化控制方法，分析了直流母线电压变化趋势与PV（Photovoltaic）发电功率的内在关系，在逆变器中采用两个不同限幅值的直流母线电压调节器，实现根据PV发电功率的变化，自然启用相应的电压调节器，确保各台逆变器优先运行在设定的最高效率点。当PV发电功率较大时逆变器再转向满载运行，从而优化模块化系统的欧洲效率，且无需增加硬件成本。
非隔离型并网逆变器拥有变换效率高，体积小、重量轻、成本低等优势，但系统中的漏电流会大幅增加，带来安全隐患。研究了非中点钳位和中点钳位两类非隔离全桥并网逆变器拓扑，旨在发现兼顾低漏电流和高效率的新型电路拓扑。基于传统H5拓扑，在光伏电池输出端和桥臂任意中点之间引入一支开关管，构造一条新的功率传输通路，提出了一种六开关非隔离并网逆变器拓扑（H6拓扑）。新拓扑在功率传输模态时，进网电流半个工频周期流过三支开关管，而另半个工频周期流过两支开关管，故相对于H5拓扑，降低了通态损耗，提高了变换效率，有利于热应力均衡，并仍满足抑制漏电流的条件；比较分析了H5、Heri（cHighly Efficient ReliableInverter Concept）和H6的拓扑结构、损耗和成本，指出H6拓扑实际是H5和Heric拓扑的折衷。H6拓扑的变换效率高于H5拓扑、但略低于Heric拓扑；共模特性优于Heric拓扑、但略劣于H5拓扑。提出由P-NPCC（Positvie-Neutral Point Clamped Cell）和N-NPCC（Negative-NetrualPoint Clamped Cell）两种基本单元构造中点钳位逆变器拓扑族的统一方法，研究了中点钳位非隔离全桥逆变器拓扑的生成机理和推演方法，揭示了中点钳位逆变器拓扑族的内在联系，按照提出的基本单元可以得到现有的中点钳位非隔离全桥光伏并网逆变器拓扑，如oH5和FB-DCBP（Full Bridge-DC Bypass），以及一族新的中点钳位非隔离全桥并网逆变器拓扑。以所提出的PN-NPC拓扑为例详细分析了其工作原理，并与oH5、FB-DCBP拓扑作了损耗的比较分析，PN-NPC拓扑共模特性与FB-DCBP相同并优于oH5，且变换效率最优。
高可靠性、高效率和高功率密度始终是电力电子装置追求的目标。总结归纳了五电平全桥逆变器拓扑生成的两种方式：①三电平全桥与输入分压电容和钳位支路组合；②三电平半桥与两电平桥臂组合。将上述拓扑生成方式推广至双降压式逆变器，提出了一族五电平双降压式全桥并网逆变器拓扑，具有高变换效率、高功率密度和低EMI（Electromagnetic Interference）的特点。研究了所提五电平双降压式全桥并网逆变器的工作原理，并对几种拓扑进行了损耗和成本的对比分析。开关管串联型五电平双降压式全桥逆变器拓扑的变换效率最高，而中点钳位型五电平双降压式全桥逆变器拓扑的电路开销最少。
对以上研究分别搭建了相应的实验平台，进行了充分的实验研究，验证了上述分析的正确性和可行性。
The initial investment and generation cost of Photovoltaic(PV) generation system are muchhigher than that of other renewable energy systems, so the efficiency improvement of both the PVgrid-tied inverters and system is a significant effort to shorten the payback time and gain the economicbenefits faster. The key technologies for high efficiency modular PV grid-tied generation systemsbased on a DC interbus are researched in this thesis.
A power conversion and management control based on an improved DC bus signaling (DBS) isproposed to optimize both the energy utilization and system stability. The operations of system arecategorized into four modes: islanding with battery discharging, grid-tied with rectification, grid-tiedwith inversion and islanding with constant voltage generation. The relastionship between systemoperation modes and system power flow is analyzed in detail. The DC bus voltage level is employedas an information carrier to determine system operation mode and mode switching. Hence, there is nocentralized controller, the system reliability is enhanced with the cost reduced. Control methods forPV converter, grid-tied converter, and battery converter are proposed with power balance of thesystem under extreme conditions, such as the islanding operation with full-charged battery,considered.
Current coupling among the non-isolated grid-tied inverters is researched and the currentdecoupling condition given, based upon analyzing the equivalent operation modes of the invertersmentioned under different topologies and modulations. Analysis reveals that the bipolar PWM (PulseWidth Modulation) inverters can be operated in parallel with current decoupling naturally. Unipolardouble frequency PWM inverters can be operated in parallel with harmonic current of switchingfrequency coupled and fundamental components decoupled. Unipolar PWM inverters can not beoperated in parallel with current coupling. Improved full bridge inverters with low leakage current canachieve current decoupling naturally in parallel operation. A control for modular grid-tied PVgeneration system to improve European efficiency is proposed. Two DC bus voltage regulators withdifferent output limits are employed in each inverter, based on the inherent relationship of dc busvoltage and PV generation power. The suitable one of the regulators is enabled naturally by the PVgeneration power to run the inverter at the highest efficiency point as the first choice, and at the fullload point only if the PV generation power high enough. As a result the European efficiency of themodular system is optimized with no additional hardware cost.
Non-isolated grid-tied inverters feature many advantages such as higher efficiency, lower cost,smaller size and weight. However, the leakage current may induce serious safety problem. In order tofind new inverter topologies with both low leakage current and high efficiency, Two types of full bridge inverter topologies which named non-Neutral Point Clamped (NPC) and NPC are researchedrespectively. A H6non-isolated full bridge PV grid-tied inverter is proposed based on the H5topology.In the power processing period, the grid-tied current flows through three power switches during oneof half line cycles, while flows through only two power switches during another half line cycle. Theconduction losses reduced and heat-stress balance benefited with the proposed H6topology than thatwith the H5topology. The power losses and costs are fairly compared among the H5topology, Herictopology and the H6topology. As a result, the efficiency of the proposed H6topology is higher thanthat of the H5topology while slightly lower than that of the Heric topology. And the common-modeperformance of the H6topology is higher than that of Heric topology while slightly lower than that ofthe H5topology.
Two types of basic switching cells, positive-NPC and negative-NPC, and a method to build NPCfull bridge PV grid-tied inverters with these two basic cells are proposed to meet the demand fornon-isolated inverter topology applied in PV generation system. A family of novel NPC non-isolatedfull bridge PV grid-tied inverters, besides existing topologies such as oH5and FB-DCBP, is derived.Operation modes of the PN-NPC topology are analyzed as an example in detail. Finally, both of theefficiency and common-mode performance of the proposed PN-NPC and Heric topologies werecompared. And the comparison results show that the proposed PN-NPC topology features betterefficiency and common-mode performance than that of the Heric topology.
High reliability, high efficiency and high power density are always the goals of power electronicdevices. Two topology generation methods for the five-level full bridge inverters are summarized asfollows:①a three-level full bridge inverter combining two input split capacitors and a clampingcircuit,②a three-level half bridge inverter combining a two-level bridge leg. By using this topologygeneration methods, a family of five-level dual buck full bridge inverter (FLDBFBI) topologies isproposed with high efficiency, high power density and low EMI. The operation principle andmodulation strategy of these proposed inverters were analyzed in details. Both the power loss and costare also fairly compared among these proposed topologies. As a result, the switch-series FLDBFBItopology has the highest efficiency, while the NPC FLDBFBI has the lowest cost.
Experimental platforms are built with the test results given in detail to verify the researchesmentioned, respectively.
针对基于直流总线的模块化光伏并网发电系统，提出了一种改进的以直流总线电压作为信息载体的功率变换管理和控制方法，旨在实现能量最优利用和系统运行模式的平滑切换。将系统分为四种运行模式，分别是孤岛运行蓄电池放电、并网运行网侧接口变换器整流、并网运行网侧接口变换器逆变、孤岛运行光伏接口变换器输出恒压。分析了系统运行模式与系统功率流的关系，设计令直流总线电压决定系统运行模式和模式切换，而无需中央控制器，降低了系统成本，提高了系统可靠性。分别给出了光伏、网侧和储能接口变换器的控制方法，使得系统在极端条件下，如孤岛运行蓄电池满电荷状态仍能达到功率平衡。
研究非隔离并网逆变器共直流和交流母线并联运行，提出了功率电路拓扑并联工作及进网电流解耦的条件。深入分析了各种非隔离全桥拓扑形式和PWM（Pulse Width Modulation）调制方式的逆变器并联运行模态，指出双极性PWM逆变器并联运行时并联逆变器间的进网电流自然解耦；单极性倍频PWM逆变器并联运行时并联逆变器的进网电流存在高频耦合，但电流基波分量解耦；单极性PWM逆变器并联运行时并联逆变器间的电流存在高频耦合，导致电流基波分量耦合，不可并联运行。低漏电流的改进型全桥并网逆变器拓扑也可实现并联逆变器间的进网电流自然解耦。提出一种模块化光伏并网发电系统欧洲效率优化控制方法，分析了直流母线电压变化趋势与PV（Photovoltaic）发电功率的内在关系，在逆变器中采用两个不同限幅值的直流母线电压调节器，实现根据PV发电功率的变化，自然启用相应的电压调节器，确保各台逆变器优先运行在设定的最高效率点。当PV发电功率较大时逆变器再转向满载运行，从而优化模块化系统的欧洲效率，且无需增加硬件成本。
非隔离型并网逆变器拥有变换效率高，体积小、重量轻、成本低等优势，但系统中的漏电流会大幅增加，带来安全隐患。研究了非中点钳位和中点钳位两类非隔离全桥并网逆变器拓扑，旨在发现兼顾低漏电流和高效率的新型电路拓扑。基于传统H5拓扑，在光伏电池输出端和桥臂任意中点之间引入一支开关管，构造一条新的功率传输通路，提出了一种六开关非隔离并网逆变器拓扑（H6拓扑）。新拓扑在功率传输模态时，进网电流半个工频周期流过三支开关管，而另半个工频周期流过两支开关管，故相对于H5拓扑，降低了通态损耗，提高了变换效率，有利于热应力均衡，并仍满足抑制漏电流的条件；比较分析了H5、Heri（cHighly Efficient ReliableInverter Concept）和H6的拓扑结构、损耗和成本，指出H6拓扑实际是H5和Heric拓扑的折衷。H6拓扑的变换效率高于H5拓扑、但略低于Heric拓扑；共模特性优于Heric拓扑、但略劣于H5拓扑。提出由P-NPCC（Positvie-Neutral Point Clamped Cell）和N-NPCC（Negative-NetrualPoint Clamped Cell）两种基本单元构造中点钳位逆变器拓扑族的统一方法，研究了中点钳位非隔离全桥逆变器拓扑的生成机理和推演方法，揭示了中点钳位逆变器拓扑族的内在联系，按照提出的基本单元可以得到现有的中点钳位非隔离全桥光伏并网逆变器拓扑，如oH5和FB-DCBP（Full Bridge-DC Bypass），以及一族新的中点钳位非隔离全桥并网逆变器拓扑。以所提出的PN-NPC拓扑为例详细分析了其工作原理，并与oH5、FB-DCBP拓扑作了损耗的比较分析，PN-NPC拓扑共模特性与FB-DCBP相同并优于oH5，且变换效率最优。
高可靠性、高效率和高功率密度始终是电力电子装置追求的目标。总结归纳了五电平全桥逆变器拓扑生成的两种方式：①三电平全桥与输入分压电容和钳位支路组合；②三电平半桥与两电平桥臂组合。将上述拓扑生成方式推广至双降压式逆变器，提出了一族五电平双降压式全桥并网逆变器拓扑，具有高变换效率、高功率密度和低EMI（Electromagnetic Interference）的特点。研究了所提五电平双降压式全桥并网逆变器的工作原理，并对几种拓扑进行了损耗和成本的对比分析。开关管串联型五电平双降压式全桥逆变器拓扑的变换效率最高，而中点钳位型五电平双降压式全桥逆变器拓扑的电路开销最少。
对以上研究分别搭建了相应的实验平台，进行了充分的实验研究，验证了上述分析的正确性和可行性。
The initial investment and generation cost of Photovoltaic(PV) generation system are muchhigher than that of other renewable energy systems, so the efficiency improvement of both the PVgrid-tied inverters and system is a significant effort to shorten the payback time and gain the economicbenefits faster. The key technologies for high efficiency modular PV grid-tied generation systemsbased on a DC interbus are researched in this thesis.
A power conversion and management control based on an improved DC bus signaling (DBS) isproposed to optimize both the energy utilization and system stability. The operations of system arecategorized into four modes: islanding with battery discharging, grid-tied with rectification, grid-tiedwith inversion and islanding with constant voltage generation. The relastionship between systemoperation modes and system power flow is analyzed in detail. The DC bus voltage level is employedas an information carrier to determine system operation mode and mode switching. Hence, there is nocentralized controller, the system reliability is enhanced with the cost reduced. Control methods forPV converter, grid-tied converter, and battery converter are proposed with power balance of thesystem under extreme conditions, such as the islanding operation with full-charged battery,considered.
Current coupling among the non-isolated grid-tied inverters is researched and the currentdecoupling condition given, based upon analyzing the equivalent operation modes of the invertersmentioned under different topologies and modulations. Analysis reveals that the bipolar PWM (PulseWidth Modulation) inverters can be operated in parallel with current decoupling naturally. Unipolardouble frequency PWM inverters can be operated in parallel with harmonic current of switchingfrequency coupled and fundamental components decoupled. Unipolar PWM inverters can not beoperated in parallel with current coupling. Improved full bridge inverters with low leakage current canachieve current decoupling naturally in parallel operation. A control for modular grid-tied PVgeneration system to improve European efficiency is proposed. Two DC bus voltage regulators withdifferent output limits are employed in each inverter, based on the inherent relationship of dc busvoltage and PV generation power. The suitable one of the regulators is enabled naturally by the PVgeneration power to run the inverter at the highest efficiency point as the first choice, and at the fullload point only if the PV generation power high enough. As a result the European efficiency of themodular system is optimized with no additional hardware cost.
Non-isolated grid-tied inverters feature many advantages such as higher efficiency, lower cost,smaller size and weight. However, the leakage current may induce serious safety problem. In order tofind new inverter topologies with both low leakage current and high efficiency, Two types of full bridge inverter topologies which named non-Neutral Point Clamped (NPC) and NPC are researchedrespectively. A H6non-isolated full bridge PV grid-tied inverter is proposed based on the H5topology.In the power processing period, the grid-tied current flows through three power switches during oneof half line cycles, while flows through only two power switches during another half line cycle. Theconduction losses reduced and heat-stress balance benefited with the proposed H6topology than thatwith the H5topology. The power losses and costs are fairly compared among the H5topology, Herictopology and the H6topology. As a result, the efficiency of the proposed H6topology is higher thanthat of the H5topology while slightly lower than that of the Heric topology. And the common-modeperformance of the H6topology is higher than that of Heric topology while slightly lower than that ofthe H5topology.
Two types of basic switching cells, positive-NPC and negative-NPC, and a method to build NPCfull bridge PV grid-tied inverters with these two basic cells are proposed to meet the demand fornon-isolated inverter topology applied in PV generation system. A family of novel NPC non-isolatedfull bridge PV grid-tied inverters, besides existing topologies such as oH5and FB-DCBP, is derived.Operation modes of the PN-NPC topology are analyzed as an example in detail. Finally, both of theefficiency and common-mode performance of the proposed PN-NPC and Heric topologies werecompared. And the comparison results show that the proposed PN-NPC topology features betterefficiency and common-mode performance than that of the Heric topology.
High reliability, high efficiency and high power density are always the goals of power electronicdevices. Two topology generation methods for the five-level full bridge inverters are summarized asfollows:①a three-level full bridge inverter combining two input split capacitors and a clampingcircuit,②a three-level half bridge inverter combining a two-level bridge leg. By using this topologygeneration methods, a family of five-level dual buck full bridge inverter (FLDBFBI) topologies isproposed with high efficiency, high power density and low EMI. The operation principle andmodulation strategy of these proposed inverters were analyzed in details. Both the power loss and costare also fairly compared among these proposed topologies. As a result, the switch-series FLDBFBItopology has the highest efficiency, while the NPC FLDBFBI has the lowest cost.
Experimental platforms are built with the test results given in detail to verify the researchesmentioned, respectively.
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