隨著網路科技的發達，雲端技術對硬體設備的需求也日益增加。資料中心含有大量的伺服器，其中含有大量的雲端計算以及資料儲存的機組，為了達到最好的功率利用率，伺服器中心前端會加裝功率校正器，使其輸入的電流呈現理想的正弦波，然而，功率校正器的前端需再安裝交流的濾波電容去因應政府對電磁干擾(EMI)的規範。除此之外，為了預防突發的停電狀況，不斷電系統(UPS)的安裝是必要，其交流側也安裝著相當大的電容。這些安裝在交流側的電容，因為大量的並聯使其容值增大，並且會與市電側的等效電感產生低頻的諧振現象，此時當市電側供電品質差或是負載端含有大量諧波源的時候，會導致用戶端電壓和市電側電流嚴重的失真，對用戶端的負載產生很大的威脅。
本篇論文介紹利用電容電壓微分成電容電流的回授控制，間接在電容側串聯一個虛擬阻尼，去抑制前面所提到的諧振現象，並搭配相位落後補償器對電容電流控制做振幅補償。此外，市電側電流的回授控制是為了去抑制由非線性負載所產生的低頻諧波電流源，以達到市電側更好的電力品質。理論分析搭配實驗測試加以印證外，並利用頻譜分析針對共振點以及較低頻率的諧波源作加入主動阻尼技術前後的比較與分析。

With the increase of the cloud computing, server farms which are the backbones of the cloud computing also develop rapidly. These server farms are equipped with a considerable amount of computer server racks, and they require PFC front-ends to draw almost perfect sinusoidal current. In the meanwhile, several AC side filter capacitors are installed to meet the harmonics and EMI standard. Along with large grid side inductors, these capacitors result in low frequency resonance in hundreds Hz to few kHz. Therefore, typical back ground harmonic distortion of the grid or neighboring harmonic-producing loads can cause significant voltage and current distortion.
In this paper, an active damping technique using capacitor current feedback control based on a shunt active power filter is explored. The proposed technique simulates a virtual resistor in series with capacitor banks to suppress the aforementioned resonance phenomenon. In addition, a lag compensator would be added to compensate the amplified magnitude caused by the capacitor current feedback control. Besides, for a better power quality, the grid current feedback control is to eliminate the harmonic current which is from non-linear load. Laboratory test results are provided to validate the performance of the proposed technique.

1. Introduction
1.1 Background 1
1.2 Motivation 1
1.3 Thesis Organization 2
2. Literature Survey
2.1 Introduction 3
2.2 Harmonic Resonance 3
2.3 Load Compensation Type of Active Power Filter 5
2.4 Voltage Detection Type of Active Power Filter 6
2.5 Grid Current Compensation Type of Active Power Filter 7
2.6 Capacitor Current Feedback for Active Damping 11
2.7 Summary 16
3. Operation Principle
3.1 Introduction 17
3.2 Capacitor Current Feedback for Active Damping. 17
3.2.1 Controller description 18
3.2.2 Controller analysis 18


3.3 Capacitor Current Feedback with Lag Compensator Design 23
3.4 Grid Current Feedback Control 27
3.4.1 Controller analysis 28
3.5 DC Bus Voltage Control. 32
3.6 Capacitor Current Feedback with Lag Compensator Control 33
3.7 Capacitor Current Lag Compensator and Grid Current Control 35
3.8 Summary. 36
4. Experiment Results
4.1 Introduction 37
4.2 Experiment Test Bench 37
4.3 Laboratory Test Results. 39
4.3.1 Capacitor Current Feedback with Lag Compensator Control 39
4.3.1.1 Operating without Non-linear Load 40
4.3.1.2 Operating with Non-linear Load 46
4.3.1.3 Discussion 52
4.3.2 Capacitor Current Feedback without Lag Compensator Control 53
4.3.2.1 Operating with Non-linear Load 54
4.3.2.2 Comparison between with and without lag compensator 57
4.3.3 Capacitor Current Lag Compensator and Grid Current Control 62
4.3.3.1 Operating with Non-linear Load 63
4.3.3.2 Discussion 69
4.3.4 Summary 70
5. Conclusion and Future work
5.1 Conclusion 71
5.2 Future Work 71
REFERENCE 72

REFERENCES

[1] S. Bhattacharya, T.M. Frank, D. Divan, and B. Banerjee, “Active filter system implementation,” Industry Applications Magazine, IEEE, vol. 4, no. 5, pp. 47–63, Sep 1998.

[2] S.-Y. Kuo, T.-L. Lee, C.-A. Chen, P.-T. Cheng, and C.-T. Pan, “Distributed active filters for harmonic resonance suppression in industrial facilities,” in Power Conversion Conference - Nagoya, 2007. PCC ’07, April 2007, pp. 391–397.

[3] R.H Simpson, “Misapplication of Power Capacitors in Distribution Systems With Nonlinear Loads—Three Case Histories” IEEE Trans. Ind. Appl., vol.41, no.1, pp. 134-143, Jan/Feb. 2005.

[4] K. Wada, H. Fujita, and H. Akagi, “Considerations of a shunt active filter based on voltage detection for installation on a long distribution feeder,” in Industry Applications Conference,2001. Thirty-Sixth IAS Annual Meeting. Conference Record of the 2001 IEEE, vol. 1, Sept 2001, pp. 157–163 vol.1.

[5] H. Akagi, H. Fujita, and K. Wada, “A shunt active filter based on voltage detection for harmonic termination of a radial power distribution line,” in Industry Applications Conference, 1998. Thirty-Third IAS Annual Meeting. The 1998 IEEE, vol. 2, Oct 1998, pp. 1393–1399 vol.2.

[6] J.-W. Huang, P.-T. Cheng, J.-C. Liao, and W.-Y. Tsai, “A shunt active power filter for harmonic isolation in a cloud computing facility,” in Future Energy Electronics Conference (IFEEC), 2013 1st International, Nov 2013, pp. 69–74.

[7] C.-L Bao, X.-B Ruan, X.-H Wang, W.-W Li, D.-H Pan, “Design of Injected Grid Current Regulator and Capacitor-Current-Feedback Active-Damping for LCL-Type Grid-Connected Inverter” in Energy Conversion Congress and Exposition (ECCE), 2012 IEEE, pp.579-586

[8] Poh Chiang Loh, D,-G Holmes, “Analysis of Multiloop Control Strategies for LC/CL/LCL-Filtered Voltage-Source and Current-Source Inverters” IEEE Transactions on Industry Application, March 2005, pp.644-6540

[9] Comanescu, Mihai, “Influence of the Discretization Method on the Integration Accuracy of Observers with Continuous Feedback” in Industrial Electronics (ISIE), 2011 IEEE International Symposium, 2011, pp.625-630.

[10] S.G. Parker, B.P. McGrath, D.G. Holmes, “A General Discrete Time Model to Evaluate Active Damping of Grid Converters with LCL Filters”, Power Electronics Conference (IPEC-Hiroshima 2014-ECCE-ASIA), 2014 International, 2014, pp.2019-2026.

[11] M. Liserre, A. Dell’Aquila, and F. Blaabjerg, “Stability improvements of an LCL-filter based three-phase active rectifier,” in Power Electronics Specialists Conference, 2002 . pesc 02. 2002 IEEE 33rd Annual, vol. 3, 2002, pp. 1195–1201 vol.3.

[12] V. Blasko and V. Kaura, “A novel control to actively damp resonance in input lc filter of a three-phase voltage source converter,” Industry Applications, IEEE Transactions on, vol. 33, no. 2, pp. 542–550, Mar 1997.