多台T型三电平逆变器并联的大功率光伏并网逆变器控制技术研究

The central PV grid-connected inverter is developing from a two-level circuit topology with the parallel-connected power semiconductor modules to that with multi-parallel-connected T-type three-level inverters. A high power PV grid-connected inverter including some high power T-type three-level inverters with the same capacities and one low power T-type three-level inverter is studied in this task, control method for power balance during the static and dynamic processes is discussed to realize the power share among the parallel-connected inverters. Automatic synchronization control of PWM carrier based on the zero-crossing point of grid voltage and synchronous modulation method and deadbeat control are presented to solve the problem of the zero-sequence circulating current. The LCL parameters of all inverters are designed in detail, reactive power compensation method based on the relationship between grid voltage and reactive current is used, and a high power inverter is replaced by a low power inverter under the condition of the weak light, so that grid-connected current THD is controlled within the range of the national standard. Finally, the integrated control strategy is given to realize the effective control among power share, zero-sequence circulating current and current harmonics, the system has the optimal ratio of performance and price and obtains the maximum benefit of power generation.

为了使光伏阵列最大限度地发电，减少对电网的电流谐波污染，集中式光伏并网逆变器正在从功率模块直接并联的两电平电路结构向多台T型三电平逆变器并联的电路结构发展。本课题以基于多台同容量大功率T型三电平逆变器和一台小功率T型三电平逆变器并联组成的大功率光伏并网逆变器为研究对象，研究系统稳态和动态过程中功率均分的协调控制方法，解决逆变器并联的功率均分问题；研究逆变器投入、电网故障瞬间恢复等动态过程中采用基于电网电压过零点和同步调制方法的PWM载波自同步控制方法和零序环流无差拍控制方法，解决零序环流问题；充分设计各逆变器LCL滤波器参数，提出基于电网电压与无功补偿电流曲线的无功补偿方法，以及利用小功率逆变器代替大功率逆变器在弱光条件下运行，解决逆变器并网电流谐波含量超标问题。最终形成统一的综合控制策略，实现功率均分、零序环流、电流谐波三者间有机协调控制，达到最佳的系统性价比和获得最大的发电效益。

为了使光伏阵列最大限度地发电，减少对电网的电流谐波污染，采用多台相同容量或不同容量的T型三电平逆变器并联的模块化电路结构，建立了单相等效电路的数学模型，研究了基于D-Σ数字控制等的并网电流控制方法，提出了系统稳态和动态过程中功率均分的控制方法，解决了逆变器并联的功率分配问题；从相间环流抑制的理念出发，研究了三相电网平衡、三相电网不平衡等条件下的逆变器并联环流抑制方法，解决了环流抑制问题；利用模块化的小功率逆变器在弱光条件下运行，解决了逆变器并网电流谐波含量超标问题。建立了基于D-Σ数字控制的功率均分、环流抑制和中点电压平衡控制的综合控制策略，实现了优良的系统性能，为实现最佳的系统性价比和最大的光伏发电效益奠定了基础。