Voltage-Balanced Control for a Cascaded 3H-Bridge Rectifier
This paper studies the CHBR (Cascaded H-Bridge Rectifier)’s DC side capacitor voltage balance control algorithm, introduces single-phase DQ coordinate transformation, deduces the mathematical model in this coordinate. This uses feed-forward decoupled cont
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Abstract This paper studies the CHBR (Cascaded H-Bridge Rectifier)’s DC side capacitor voltage balance control algorithm, introduces single-phase DQ coordinate transformation, deduces the mathematical model in this coordinate. This uses feed-forward decoupled control strategy to keep voltage and current of AC side in the same phase, puts forward an improved algorithm to balance DC capacitor voltage even if the loads of CHBR are imbalanced. Finally, establishes a simulation model of three cells’ CHBR. The simulation results indicate that this improved algorithm can reduce the switching frequency effectively, and balance the DC voltage of every module much better. Keywords Cascaded H-bridge rectifier Voltage control Simulink
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Bridge circuits
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Power factor
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1 Introduction The cascade multilevel converter is used to control the high voltage and large-capacity electric drive. It is easy to control and has modular structure, good expansibility. The H-bridge circuit is the basic power conversion unit. Several units are cascaded and become a simple cascaded circuit [1–4]. H-bridge cascaded multilevel converter DC side is connected with capacitor, and isolated from each other. So there are multigroup independent DC bus voltages. Furthermore, each H-bridge converter unit is a nonlinear, multivariable, strong coupling system, and each of the converter units has different parallel loss, switching loss, and modulation. Those problems make DC capacitor voltage of each converter unit unbalance. So how to balance the DC capacitor voltage is a research focus of cascaded H-bridge multilevel topology [5–8]. Z. Fu (✉) ⋅ B. Zhang ⋅ X. Xiong School of Electrical and Electronic Engineering, Henan Polytechnic University, Jiaozuo 454003, China e-mail: [email protected] © Springer Science+Business Media Singapore 2016 Y. Jia et al. (eds.), Proceedings of 2016 Chinese Intelligent Systems Conference, Lecture Notes in Electrical Engineering 405, DOI 10.1007/978-981-10-2335-4_52
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The balanced control of DC capacitor is related to the output waveform’s quality, active, and reactive power. Because of the cascaded topology, current of each power unit is equal and it means that DC output voltage must be adjusted by the same current. This feature makes it difficult to control the DC output voltage, what is more may appear as system stability problems in some cases [9, 10]. There are two main methods to solve this problem: complex modulation method and closed-loop control method. Complex modulation method contains several kinds of ways such as two-dimensional modulation method, space vector pulse width modulation method, exchange balanced modulation method, and so on [11–14]. Those methods can balance the DC capacitor quickly, accurately, and effectively. But the modulation strategies need to be designed according to the specific converter structure. So it is hard to be extended to multi-cascaded H-bridge topology. Another one is closed-loop control method. Its basic thought is to closed-loop control the capacitor voltage
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