混合多梯度光伏并网逆变方法及控制研究

Affected by light, temperature and other environmental factors, there are various problems that exists in photovoltaic array output voltage and power, such as strong fluctuation, large variation range, etc. Therefore, this project intends to take the bidirectional expansion of power operation range of PV grid-integration system as a starting point, to carry out research on hybrid multi-gradient grid-inversion method and control techniques for photovoltaic generation system. Firstly, according to the topology combination constraints, a family of complex inverter topologies that can meet the requirements of multi-gradient grid-integration is built, its unified constitution law explored, and the working mechanism of its hybrid multi-gradient grid-integration is revealed. And then, on the basis of research on grid-connected inversion control of deferent topology working steps and power balancing control of topology sub-units, the dynamic adjustment mechanism among deferent working modals of topology family is determined. Furthermore, the flexible transition strategy among deferent working modals is studied, making the PV grid-integrated generation system work sustainably and efficiently under the condition of large variation of PV array output voltage. Finally, an experimental platform is built to verify the effectiveness of complex photovoltaic inversion topology family and its multi-gradient grid-integration control method. The conduction of this project will play a positive promoting role to the working performance improvement of PV grid-integrated generation system, and the project ideas and methods adopted can also be taken as a helpful reference to other new energy generation systems such as wind generation.

受光照、温度等环境因素的影响，光伏阵列输出电压与功率存在波动性强、变化范围大等问题。为此，本项目拟以拓展光伏并网发电系统功率运行范围的上、下限为出发点，开展混合多梯度光伏并网逆变方法及其控制技术的研究。首先，根据拓扑组合约束条件，构建一族满足多梯度并网要求的复合逆变拓扑，并探索其统一构成规律，揭示其混合多梯度并网工作的机理；然后，在拓扑族不同工作梯级并网逆变控制及拓扑族子单元功率均衡控制研究的基础上，确定拓扑族不同工作模态间的动态调整机制，研究各工作模态间的柔性过渡策略，实现光伏并网发电系统在光伏阵列输出电压大范围变化下的多梯度持续、高效运行。最后，搭建实验平台对复合光伏并网逆变拓扑族及其多梯度并网控制方法的有效性进行实验验证。项目的开展将对光伏并网发电系统工作性能的改善起到积极的推动作用，且项目的思路和采取的方法也可以为风力发电等其他新能源发电形式提供借鉴。

受光照、温度等环境因素的影响，光伏阵列输出电压与功率存在波动性强、变化范围大等问题。为此，本项目以混合多梯度光伏并网逆变方法及其控制技术为切入点，从并网逆变拓扑、逆变器调制方法以及并网控制策略等角度展开研究。分析光伏阵列外部条件变化对光伏发电系统最大功率点跟踪策略的影响，并提出一种基于虚拟功率预估的MPPT改进策略，提出的MPPT策略有效解决了在外部条件突变时的误判问题，可以较好地实现最大功率点跟踪。根据逆变器拓扑组合约束条件，构建两种满足多梯度并网要求的复合逆变拓扑，并分析其混合多梯度并网的工作机理。分析混合多梯度并网逆变拓扑在不同并网梯级的工作模态及其开关通路，制定不同并网梯级子单元工作模态下的调制策略，通过多载波PWM调制及其复用实现不同工作模态间的动态过渡。提出一种自均压单相九电平光伏逆变器及其调制策略，能够以较少的开关功率器件产生更多的电平数，简化了多电平逆变器拓扑的结构，降低了系统的成本，并且提出的多电平逆变器具有电容电压的自平衡能力。从系统并网控制的角度，分析光照、温度等外部环境变化下的系统输出功率特性对电网的影响，给出复合储能型光伏并网发电系统的实现方案及并网控制方法，实现系统并网功率高低频波动分量的平滑控制。项目取得的结果对光伏并网发电系统工作性能的改善将起到积极的推动作用，且项目的思路和采取的方法也可以为风力发电等其他新能源发电形式提供借鉴。