Current-Mode Control with Asynchronous Sigma-Delta Modulation for Single-Phase Grid-Connected Inverters

近年來，由於結合再生能源之微型電網的需求與發展，市電併聯換流器成為了重要的電力調節設備。為了提高微型電網的可靠度，換流器的電流控制需達到雙向功率潮流與無效功率補償等功能。因此，本論文主旨在提出兩組以遲滯控制為基礎之新型電流控制策略。其中一組電流控制係採用非同步和差調變技術來產生換流器功率開關所需之脈波訊號。本論文之研究成果是最先將非同步和差調變技術應用在市電併聯換流器之電流控制上。因為非同步和差調變的變頻切換特性，可以加快換流器的動態響應速度以及降低功率開關切換時所造成的電磁干擾成分。此外，與傳統遲滯電流控制相較之下，其電力級之電路參數變動對切換頻率變動的影響也較小。另一方面，本論文亦開發出具定頻切換之非同步和差調變技術並且應用於換流器之電流控制上，其可以保有快速動態響應之特性。本論文針對所提出之非同步和差調變型電流控制與定頻式-非同步和差調變型電流控制的操作原理與數學推導做詳盡的描述。最後，將所提出之兩組電流控制策略應用於一千瓦之單相市電併聯換流器雛型機，並且透過電腦模擬與實測結果來驗證此換流器應用於交流與直流微型電網上的效能。The objective of this dissertation is to develop two novel hysteresis-based current control strategies for single-phase grid-connected inverters (GCIs). One of the proposed current control strategies adopts the asynchronous sigma-delta modulation (ASDM), which consists of an integrator and a hysteresis comparator, to generate the gating signals for the power switches of the GCI. The usage of ASDM for the GCI’s output current control is first reporting in this dissertation. Since the ASDM has the variable switching frequency feature, it can improve the dynamic response and reduce the electromagnetic interference noise. Of particular importance, its switching frequency variation is much less sensitive to the power-stage parameters comparing to the conventional hysteresis current control. The other proposed current control strategy is to develop the constant-frequency ASDM (CF-ASDM) for the GCI’s output current control, which maintains the advantage of quick dynamic response. The operation principle and mathematic derivations of the proposed current-mode ASDM and CF-ASDM control strategies are developed thoroughly. A 1 kW GCI prototype for either ac or dc microgrid applications is built and tested. Computer simulations and experimental results are presented to confirm the theoretical results.中文摘要....................................................I Abstract..................................................II Table of Contents........................................III List of Figures...........................................VI List of Tables............................................XI Abbreviations............................................XII Chapter 1 Introduction....................................1 1.1 Background...........................................1 1.2 Motivation...........................................4 1.3 Dissertation Outline.................................6 Chapter 2 Review of Previous Current Control Strategies of Grid-Connected Inverters................................9 2.1 Grid-Connected PV Systems............................9 2.2 Grid-Connected Inverters............................12 2.2.1 Transformer-Type Grid-Connected Inverters......14 2.2.2 Transformerless Grid-Connected Inverters.......15 2.3 Current Control Strategies..........................19 2.3.1 Hysteresis Current Controls....................19 2.3.2 Ramp Comparison Controls.......................23 2.3.3 Predictive Current Controls....................27 2.4 Summary.............................................29 Chapter 3 The Current-Mode Control with Asynchronous Sigma-Delta Modulation....................................31 3.1 Introduction........................................31 3.2 Delta Modulation....................................32 3.3 Sigma-Delta Modulation..............................34 3.4 Asynchronous Sigma-Delta Modulation (ASDM)..........38 3.5 The Proposed Constant Frequency-Asynchronous Sigma- Delta Modulation (CF-ASDM)..........................43 3.6 Computer Simulations and Experimental Verifications ....................................................48 3.7 Summary.............................................59 Chapter 4 The Proposed Current-Mode ASDM Scheme for Single-Phase PV Inverters with Reactive Power Control.....61 4.1 Introduction........................................61 4.2 Simplified Reactive Power Control...................65 4.2.1 Simplified Power Calculation...................65 4.2.2 Smooth Power Adjustment........................68 4.3 Single-Phase PV Inverters with the Proposed Control Strategy............................................75 4.4 Stability Evaluation with Small Signal Analysis.....77 4.5 Computer Simulations and Experimental Verifications ....................................................84 4.6 Summary.............................................95 Chapter 5 The Proposed Current-Mode CF-ASDM Scheme for Modularized Bi-Directional Grid-Connected Inverters.......97 5.1 Introduction........................................97 5.2 Bi-Directional Grid-Connected Inverters with the Proposed Control Strategy...........................99 5.3 DC Bus Voltage Regulation..........................103 5.4 Modularized Techniques.............................106 5.5 Computer Simulations and Experimental Verifications ...................................................108 5.6 Summary............................................121 Chapter 6 Conclusions and Suggested Future Research.....123 6.1 Summary and Major Contributions....................123 6.2 Suggestions for Future Research....................125 References...............................................127 Vita.....................................................14