Design of Neutral-Point Voltage Controller of a Three-Level NPC Inverter With Small DC-Link Capacitors
Design of Neutral-Point Voltage Controller of a Three-Level NPC Inverter With Small DC-Link Capacitors
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DOI：
10.1109/tie.2012.2202352
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发表时间：
2013-05
影响因子：
7.7
通讯作者：
R. Maheshwari;S. Munk‐Nielsen;S. Busquets-Monge
中科院分区：
文献类型：
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作者：
R. Maheshwari;S. Munk‐Nielsen;S. Busquets-Monge
提出了一种采用小直流侧电容的中点钳位式三电平逆变器。逆变器需要零平均中点电流才能获得稳定的中点电压。即使中性点电流为零时，小直流侧电容器也不能保持电容电压平衡。这可能是由于电路中存在的非线性造成的。这就需要对中点电压进行快速控制。提出了一种简单的基于载波的调制策略，允许将中点电压动态建模为逆变器输出功率的连续函数。这一连续模型表明，中点电流与逆变器输出功率成正比，它使经典控制理论能够用于中点电压控制器的设计。在连续模型的基础上，设计了一种用于中点电压控制的简单比例积分控制器。讨论了优化性能的设计方法。所提出的调制策略和控制器的实现非常简单。该控制器在一台7.5kW的感应电机驱动系统中实现，只有14个μF直流链电容器。实验结果表明，中点电压控制器实现了快速稳定的性能，从而验证了所提出控制方法的有效性。
A neutral-point-clamped three-level inverter with small dc-link capacitors is presented in this paper. The inverter requires zero average neutral-point current for stable neutral-point voltage. The small dc-link capacitors may not maintain capacitor voltage balance, even with zero neutral-point current. This may happen due to nonlinearities present in the circuit. This requires a fast control of the neutral-point voltage. A simple carrier-based modulation strategy which allows modeling of the neutral-point voltage dynamics as a continuous function of power drawn from the inverter is proposed. This continuous model shows that the neutral-point current is proportional to the power drawn from the inverter, and it enables the use of a well-established classical control theory for the neutral-point voltage controller design. A simple proportional integral controller is designed for the neutral-point voltage control on the basis of the continuous model. The design method for optimum performance is discussed. The implementation of the proposed modulation strategy and the controller is very simple. The controller is implemented in a 7.5-kW induction machine-based drive with only 14 μF dc-link capacitors. Also, the experimental results show that fast and stable performance of the neutral-point voltage controller are achieved and thus verify the validity of the proposed control approach.