A Comprehensive Harmonic Analysis and Control Strategy for Improved Input Power Quality in a Cascaded Modular Solid State Transformer
A Comprehensive Harmonic Analysis and Control Strategy for Improved Input Power Quality in a Cascaded Modular Solid State Transformer
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DOI：
10.1109/tpel.2018.2873201
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发表时间：
2019-07
影响因子：
6.7
通讯作者：
N. Gorla;S. Kolluri;Merlin Chai;S. K. Panda
中科院分区：
文献类型：
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作者：
N. Gorla;S. Kolluri;Merlin Chai;S. K. Panda
在三级级联模块化固态变压器（CMSST）中，级联多电平整流器输出直流母线电压不平衡是一个常见问题，原因是二级参数不可避免的失配。为了平衡直流母线电压，需要一级电压平衡控制（VBC）或二级功率平衡控制（PBC）。本文对CMSST在电压和PBC两种方案下的输入电能质量进行了深入的理论分析。分析了CMSST的电网侧多电平电压，强调了在一级中使用VBC的局限性。然后在数学上证明，通过在阶段2中使用PBC，电网电流中基于开关频率的谐波显着降低。使用PLECS软件对3.3 kv， 50 kva的CMSST进行了仿真研究，以证实所提出的分析。实验验证在750-VA单相CMSST实验室样机上进行，第2阶段参数失配率为20%。结果表明，在负荷为50%时，电网总谐波失真（THD）由6.65%降至3.8%。本文为设计人员选择合适的CMSST平衡控制器提供了指导。
In a three-stage cascaded modular solid state transformer (CMSST), unbalanced dc bus voltages at the output of cascaded multilevel rectifier is a common issue due to inevitable parameter mismatch in stage-2. To balance the dc bus voltages, either voltage balance control (VBC) in stage-1 or power balance control (PBC) in stage-2 is necessary. In this paper, an in-depth theoretical analysis to investigate the input power quality of the CMSST in the presence of voltage and PBC schemes is presented. The grid-side multilevel voltage of the CMSST is analyzed to highlight the limitation of using VBC in stage-1. It is then mathematically proven that the switching frequency based harmonics in the grid current are significantly reduced by using the PBC in stage-2. Simulation studies of a 3.3-kV, 50-kVA CMSST are carried out using the PLECS software to substantiate the proposed analysis. Experimental verifications are performed on a 750-VA single-phase CMSST laboratory prototype for a 20% parameter mismatch in stage-2. It is found that the grid current total harmonic distortion (THD) is reduced from 6.65% to 3.8% at 50% load by using PBC in stage-2. This paper provides guidelines for the designer to choose appropriate balance controllers for the CMSST.