【作者】 吴春华；

【导师】 陈国呈；

【作者基本信息】 上海大学 ， 电力电子与电力传动， 2008， 博士

【摘要】 在能源枯竭及环境污染问题日益严重的今天,光伏发电是未来可再生能源应用的一种重要方法。本文以光伏逆变技术为研究对象,对光伏系统最大功率点跟踪方法、光伏智能充电控制策略、光伏并网系统拓扑结构与控制方法、光伏并网与有源滤波统一控制方法等问题进行了深入研究。在扰动观测法的基础上,提出了一种直接电流控制最大功率点跟踪方法,通过检测变换器输出电流进行最大功率点跟踪控制,简化控制算法,同时省去了扰动观测法中的电压和电流传感器,降低系统成本。研究了一种实用的光伏系统蓄电池充电控制策略,将最大功率点跟踪与智能充电控制有机结合在一起,充分利用光伏电池的输出功率,缩短充电时间,提高充电效率;研究了一种全数字式逆变器,通过电压有效值外环和瞬时值内环的双闭环控制,既能保证系统输出电压的稳态精度,又能保证瞬变负载条件下的动态特性。研制了一套3kW光伏独立发电系统并进行了实验验证。针对住宅型光伏并网逆变器体积小、性能价格比高的要求,研究了一种基于导抗变换器的并网逆变器拓扑结构,相比于传统电流型逆变器,本拓扑省去了笨重的电抗器,同时利用高频变压器进行能量传递和电气隔离,进一步降低了系统损耗和体积,降低系统成本。经研究发现,由于导抗变换器的固有特性,采用传统的SPWM调制方法将导致并网逆变器输出平顶饱和的非正弦电流,造成对电网的谐波污染,提出了一种新型改进调制模式。该方法可以实现高功率因数、低谐波并网发电。根据上述理论分析,研制了一台3kW单相光伏并网逆变器,实验结果验证了理论分析的正确性。研究了一种三相电流型并网逆变器拓扑结构及其控制方法,采用改进调制模式对其进行控制,在谐波抑制方面取得了满意的效果。提出的三相并网逆变方案,相比于传统三相并网逆变器,具有如下显著优点:系统中任意一相都是一个独立的子系统,不受其它相影响,即使在某一相或某两相损坏的情况下,剩余相也能正常运行,增加了系统的冗余性;在三相电网不平衡情况下,本方法也能提供稳定的三相电流,增加系统抗电网波动能力。初看起来本方案使用的导抗变换器和变压器有3套,但是每相承受的功率容量只有系统总功率的三分之一,这样可以选用较小容量的器件,有利于高频电感和变压器的制作和生产。提出了一种基于导抗变换器的三相电流型逆变器实现方案,利用导抗变换器将输入直流电压变换为高频正弦电流,经高频变压器隔离及电流等级变换后进行裂相调制,输出为三相正弦电流。该方法不仅省去了传统电流型逆变器直流侧电抗器,而且采用高频变换进行功率传输,减小了隔离变压器及输出滤波器的体积,有利于装置的小型化和降低成本。针对光伏电池输出电压较低的问题,研究了一种单级式三相升压型并网逆变器,通过一级变换同时实现升压和DC/AC变换功能,并且提出了一种基于DSP芯片的控制策略,本方法仅用一个电压传感器就能替代原先的三个电压传感器;每个载波周期短路相只进行一次开关动作,同时任何时刻只有2个开关管导通,可有效降低系统的开关损耗和导通损耗;由于采用DSP控制,具有控制灵活、稳定性高、成本低、并网电能质量好,便于功率调节等优点。提出了一种光伏并网与有源滤波兼用的统一控制策略,在同一套装置上既实现光伏并网发电,又实现谐波补偿,克服目前的光伏发电装置白天发电、夜间停机的不足,提高系统利用率。详细分析了无功电流和谐波电流的检测方法、光伏并网发电有功指令电流的生成方法及电流环控制器和电压环控制器的设计方法,并对光伏并网发电与有源滤波统一控制模式和单一有源滤波模式进行了讨论,仿真和实验结果验证了所提出的系统结构及控制策略的正确性和可行性。更多还原

【Abstract】 With the global environmental pollution and the increasing serious energy crisis today, photovoltaic (PV) power generation is becoming one of the most promising renewable energy technologies. The research in this paper involves Maximum Power Point Tracking (MPPT) techniques, intelligent charge control strategy, topology and control method of the PV grid-connected power generation and unification control method of PV grid-connected generation and active power filtering, etc.Direct current MPPT control strategy is proposed based on disturbance observer method. By directly detecting output current of PV converter, not only voltage sensors and current sensors in disturbance observer method are reduced, but also simple control algorithm and low cost are realized.A practical lead-acid battery charge control strategy combined with MPPT technique for PV system is studied. The novel method can promote PV cell efficiency, shorten battery charge time and improve charge efficiency. A digital control technique for the inverter is described, which is based on available value voltage and instantaneous voltage dual-loop control. Steady-state accuracy and dynamic performance are ensured at the same time by this control method. A 3kW prototype is designed and tested in the lab, and the experimental results verified the proposed control strategy.Considering small volume and low cost of resident PV grid-connected inverter, the topologies of grid-connected based on immittance converter are studied. Compared with the traditional current source inverter, high-frequency inductor and transformer in the proposed inverter replace the power frequency inductor and transformer. Low power loss, small volume and low cost are realized in the new inverter.As to inherent characteristic of immittance converter, this paper shows that the output current of grid-connected inverter is non-sinusoidal under the conventional SPWM method, which leads to harmonic pollution in public supply networks. An improved modulation method is proposed. A high power factor and low harmonic grid-connect power generation are realized by this way. A 3kW single-phase PV grid-connected inverter prototype is designed based on above theory analysis. The feasibility and validity are proved by experimental results.The topologies and control strategy of three-phase current source grid-connected inverter are studied. An improved modulation strategy is adapted and a satisfied solution is achieved on harmonic suppression. Compared with conventional three-phase grid-connected inverter, the novel inverter has the obvious characteristics as following: any phase of the inverter can work normally even if the other one or both phases are destroyed, which enhances the system redundancy. Under unbalanced grid, the inverter also can provide a stable three-phase current, which strong anti-electricity fluctuation capability. Though three sets of immttance converter and transformer are used, power capacity of every phase is only one third of the inverter total power capacity. Consequently, smaller capacities high-frequency inductor and transformer can be selected.A three-phase current source inverter is presented based on immittance inverter. To utilize of characteristics of immittance converter, DC voltage is converted into sine-wave high frequency current and is isolated by high-frequency transformer, then three-phase sine-wave current source is achieved through cycle-converter modulation. Not only the DC input inductor is reduced but also power is transmitted by high frequency converter. Consequently, the volume of output filter inductor and isolated transformer is declined; small volume and low cost are realized.Due to the low output voltage of PV cell arrays, a novel single-stage three-phase boost-type grid-connected inverter is studied. The simulation and experiment results show that current-source grid connection with a high power factor can be realized by single-stage boost DC/AC conversion. Moreover, the power frequency inductors in traditional current-source inverter are removed and only two switches are communicated at any time. Therefore, the proposed inverter has advantages of flexible control, high stability, low cost and high quality grid current based on the DSP control.The unification control method of PV grid-connected power generation and active power filtering are proposed. PV grid-connected generation and harmonic compensation are realized on the same prototype, which overcomes that PV grid-connected power generation equipment is inoperative at night and improves the system efficiency. Reactive current and harmonic current detection method, active current of PV power generation calculation method, current loop controller and voltage loop controller deign method are analyzed in detail. Furthermore, the unification control method and single active power filtering control method are discussed individually. The feasibility of control strategy and system topology is verified by the simulation and experimental results.更多还原