單相雙向LCL換流器研製

Design and Implementation of Single-Phase Bi-Directional Inverter with LCL Filter

陳昱翔(Chen, Yi Hsiang)

指導教授 ： 吳財福

國立清華大學/電機資訊學院/電機工程學系/碩士(2015年)

https://doi.org/10.6843/NTHU.2015.00409

摘要

本論文使用全橋架構換流器，採用分切合整數位控制以得到精確之電流命令和達成追控特性，以及使用LCL濾波器來降低因開關切換造成的漣波電流注入市電。本研究之主要貢獻可摘要如下：其一，由於電感值會隨電流變化，使得電流漣波依不同切換週期會有所不同，因此本文利用改變開關切換頻率的方式來降低電流漣波，並推導於單相及三相換流器架構上的相關公式；其二，考慮寬感值變化，根據電氣規格來設計所需之鐵芯，計算所需之匝數及衰減率，並允許感值變化二至五倍，可有效減少電感體積及成本。再者，藉由變頻及感值變化，利用模擬計算變換開關切換頻率之範圍。
其三，由於LCL為三階濾波器，其存在著穩定性問題，容易發散和振盪，這將轉而導致電網電流失真。因此，藉由設計換流器之Li、Cs及Lg參數來避開諧振頻率，使諧振頻率範圍介於十倍市電頻率及十分之一的切換頻率間；其四，當市電存在顯著的電壓諧波時，同樣會影響電網電流，造成電網電流失真，並且濾波器中電容電流也會含有諧波成分。爲了使注入市電的電流是基頻弦波電流，換流器的電感電流追蹤命令必須更新為包含補償電流之參考電流，因此本研究提出了基於分切合整控制的電容電流補償機制，此控制機制將分切合整計算所得的參考電流命令與濾波電容電流相加得到新的參考電流命令，使得電流諧波能夠由靠近換流器之濾波電感來補償，從而降低電網電流諧波。最後實作出一部5 kW單相雙向換流器，並經由實測結果驗證本研究所提出之理論與換流器操作之可行性。

關鍵字

LCL濾波器 ； 分切合整數位控制 ； 電容電流補償 ； 變頻切換 ； 鐵芯選用

並列摘要

This research adopts a full-bridge inverter and division-summation (D-Σ) digital control to yield precise current command and achieve tight tracking and control characteristics. The inverter is associated with an LCL filter to reduce current ripple. The major contributions of this research can be summarized as follows. First, since the filter inductance varies with its current, current ripple will be different at different switching periods. Therefore, this research uses a variable switching scheme to limit the current ripple, and derives the related control laws for single-phase and three-phase configurations. Second, the inductor core is selected according to the specifications, and inductance varies from two to five times. It can reduce the volume of the inductor and cost.
Third, LCL filter is easy to diverge and oscillate because it’s a third-order filter. Hence, let the resonant frequency be in a range between ten times the line frequency and one-tenth of the switching frequency to avoid the resonant problems by designing the filtering parameters of Li, Cs and Lg. Forth, since there typically exist grid voltage harmonics, the injected grid current will contain harmonic components due to the effect of the LCL-filter-capacitor. This thesis presents an extended application of the D-Σ digital control associated with a filter-capacitor-current compensation to reduce the injected grid-current harmonics. The control laws of the inverter with the D-Σ digital control and compensation approach are derived in detail, and the reduction of grid-current harmonics is analyzed. Finally, simulated and experimental results measured from a 5 kW single-phase bi-directional inverter have verified the feasible application of the D-Σ digital control and proposed compensation.

並列關鍵字

LCL-fiter ； D-Σ digital control ； filter-capacitor-current compensation ； variable frequency ； choice of core

參考文獻

[1] IEEE Application Guide for IEEE Std. 1547, IEEE Standard for Interconnecting Distributed Resources With Electric Power Systems, IEEE 1547.2-2008, 2009.

[2] IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems, IEEE 519-1992, 1993.

[3] M. Liserre, F. Blaabjerg, S. Hansen, “Design and control of an LCL-filter based three-phase active rectifier,” IEEE Transactions on Industry Applications, vol. 41, no. 6, pp. 1281-1291, Sept. 2005.

[4] E.J. Bueno, F. Espinosa, F.J. Rodriguez, J. Urefia, S. Cobreces, “Current control of voltage source converters connected to the grid through an LCL-filter,” in IEEE PESC, vol. 1, pp. 68-73, Jun. 2004.

[5] M. Liserre, R. Teodorescu, F. Blaabjerg, “Stability of photovoltaic and wind turbine grid-connected inverters for a large set of grid impedance values,” IEEE Transactions on Power Electronics, vol. 21, no. 1, pp. 263-272, Jan. 2006.