【作者】 张纯；

【导师】 陈民铀；

【作者基本信息】 重庆大学 ， 电气工程， 2011， 硕士

【摘要】 用电负荷不断增长、用户对电能质量与可靠性的要求不断提高、电网设备老化、能源利用效率存在瓶颈、环保问题日益突出,这些都已成为当今世界各国电力工业面临的严峻挑战。微网(Microgrid)作为一种整合利用分布式电源的有效形式,既能实现对可再生能源的充分利用,又能通过灵活的控制提高供电质量与可靠性,因而受到了广泛关注。运行控制是微网的关键技术之一,良好的控制策略是微网诸多技术经济优势得以发挥的前提。本文围绕微网孤岛、并网两种模式的运行控制策略展开研究,在电源层面上将分布式发电DG(Distributed Generation)分为功率间歇型并网DG和功率可控型组网DG,并网DG执行最大功率跟踪控制,而组网DG则承担起形成微网电压、频率的任务,对微网的运行特性起主导作用。以直驱风力发电系统作为并网DG的典型代表,建立了系统的完整模型,对双PWM变换器的控制策略进行了深入研究,机侧变换器控制实现风机的最大功率跟踪,网侧变换器控制实现入网功率的有功无功(PQ)解耦。对于组网DG,本文用理想直流电压源对“原动机+储能元件”的组合进行等效,着重研究其并网逆变器的控制策略。组网DG的控制策略以下垂控制为基础,针对下垂控制无功均流性能的缺陷,本文提出补偿线路压降的无功-电压(Q-V)下垂控制方法,有效改善了孤岛运行时下垂控制的无功均流性能。并在下垂控制器的基础上设计了逆变器预同步控制单元,用于实现组网DG的平滑并联。针对微网并网运行的需要,本文在组网DG的下垂控制器中引入下垂额定点调整环以稳定其功率输出,实现PQ控制。通过该环节的投切实现组网DG在PQ控制与下垂控制之间的切换,控制上具有较强的连续性,这对于微网运行模式的平滑切换十分有利。在系统级的运行控制层面上,采用微网分层控制体系,以组网DG的下垂控制和并网DG的PQ电流解耦控制作为底层控制,在此基础上利用微网管理器对DG和负载进行综合调控,并加入了频率恢复算法改善孤岛系统的频率质量。在分层控制体系下,微网能够实现多种运行方式,可以根据需要灵活选择,并能在孤岛与并网模式之间实现平滑切换,切换过程满足对重要负载的不间断供电。在微网通信失效的情况下,底层控制作为后备仍然能够维持微网的稳定运行。最后,搭建了基于Matlab/Simulink的微网仿真平台,对微网孤岛、并网以及模式切换等多种运行工况进行了仿真实验,并对仿真结果进行了详细的分析,验证了所提出的微网架构和控制策略的有效性。更多还原

【Abstract】 Electrical loads are continually growing while the requirements for power quality and reliability are increasingly high. The aging power equipments, bottlenecks of energy efficiency and environment problems are all becoming great challenges to the world’s power industry. Microgrid has drawn a lot of attention for it has good potential to achieve the full utilization of renewable energy, and improve the quality of power supply. Operation and control is one of the key technologies of microgrid, good control strategy ensures the advantages of microgrid.This thesis focuses on the control strategies for both islanded and grid connected operation of microgrid. On the level of distributed generation control, DGs are divided into two categories, Grid-Forming DG (GFDG) and Power Injection DG (PIDG), GF DG forms the microgrid while the PIDG usually implements MPPT control, the operation characteristic of microgrid is dominated by the GFDGs. The direct-drive wind power generation system is modeled as a typical PIDG, and the control scheme of the back to back PWM converter is investigated, the generator side converter achieves maximum wind power tracking while the grid-side converter achieves PQ decoupled control. As for the GFDG, a simplified model was implemented using an ideal DC voltage source instead of the combination of prime mover and storage, the focus was on the control of the grid-tied inverters. The control scheme of GFDG was based on droop control, and it is improved by adding the line voltage drop compensation into the Q-V droop characteristic to achieve the precise sharing of reactive power. A pre-synchronizing control unit was designed base on the droop controller to achieve the smooth connection between the GFDGs and the main grid. Considering the operation features of grid connected operation mode of microgrid, a droop setting adjustment loop was added to the droop controller to implement PQ control of the GFDG. The control mode could be changed by switch this loop. The control scheme has a strong continuity between the 2 modes, which is favorable for the smooth operation mode transfer.At the system operation level of the microgrid, a hierarchical control structure was implemented. The local control of GFDG and PIDG was the basis of microgrid control and the whole network was regulated by the Microgrid Manager, a frequency restoration algorithm implemented to improve the frequency quality of the islanded microgrid. under the hierarchical control system, the microgrid can achieve a variety of operation modes and flexibility to choose it according to need, and can switch between the 2 operation modes smoothly. The switching process guarantees the uninterrupted supply of critical loads. In case of communication failures, the underlying control can maintain the stability of microgrid operation as a backup.Finally, a simulation platform of microgrid was built base on Matlab Simulink software. Several operation conditions were simulated in both islanded and grid connected modes as well as the transferring of operation mode to verify the control strategies, the simulation results was discussed in detail.更多还原