Voltage Balance Control and Dynamic Response Analysis for Series-Connected Chargers
| Autor: | Chih-Chung Huang, 黃志忠 |
|---|---|
| Rok vydání: | 2019 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 107 In recent years, the demand for electric vehicles and energy storage systems has led to the rapid development of the lithium-ion battery. In order to meet the needs of various applications and different powers, the voltage range of lithium-ion battery arrays is very wide, generally ranging from 200V to 1000V, which also drives research of charger with wide range of output voltage. However, it is not easy to satisfy both the high output voltage range of the charger and the high conversion efficiency. From the perspective of increasing the flexibility of system configuration, this dissertation proposes a method to connect multiple chargers in series to expand the output voltage and achieve the balance of the output voltage of each charger when operating in constant current mode. In order to achieve high configuration flexibility, current sharing of chargers (converters) connected in parallel has been developed for more than 20 years, but voltage balance of chargers connected in series is rarely mentioned in the study. Therefore, the research topic of this dissertation is putting on voltage balance analysis and control when chargers are operating in CC mode and connected in series. The complete analysis steps include the construction of the small signal model of the charger, interpretation of the phenomenon of voltage imbalance in the series of chargers, design criterion for voltages balance control, and analysis of interaction between series chargers and load. A general hard-switching full-bridge converter is used to realize the charger function, and a small-signal model that can accurately estimate the leakage inductance effect of the transformer is proposed. The Norton equivalent circuit of the charger operating in constant current mode is obtained to explain the voltage imbalance phenomenon when the chargers are connected in series. According to the analysis, if we want to reduce the series voltage imbalance, we can decrease the output current or output impedance of the charger with higher output voltage, on the contrary, we can increase the output current or output impedance of the charger with lower output voltage. Using the rule, this dissertation proposes the average voltage balance control strategy to minimize the difference between the output voltage and the average voltage of the system by feeding back the average voltage of the series system to each charger to regulate output current of the charger and achieve the voltage balance function. Through a complete analysis of the system, the virtual loop gain including the voltage balance compensator can be obtained. Applying this virtual loop gain, combined with the theory of automatic control, the voltage balance compensator that can achieve charger output voltage equalization can be designed. In addition, this dissertation also derives an equation for analyzing the interaction between the charges and the load. The equation includes the output impedance of the series system and the input impedance of the load. It can be used as another virtual loop gain. This virtual loop gain can be used to estimate system stability when the charger system is connected to the load. Through the above design criteria, this dissertation uses two chargers in series to verify the accuracy of the conclusion. First, using the design criterion of the voltage balance compensator to realize the series charger system with different voltage balance bandwidth, the theoretical results are compared with the experimental results. The results show the correctness of the conclusion. Next, using the output impedance of the series system and the input impedance of the load, the other virtual loop gain also accurately predicts the stability of the overall system when the series system is connected to the load. By using the methods proposed in the dissertation, the system of chargers in series not only has voltage balance function, but also has high response speed and high stability. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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