Control and Filter Design of Single-Phase Grid-Connected Converters

Weimin Wu is a Professor in the Department of Electrical Engineering at the Shanghai Maritime University in China. Frede Blaabjerg is a Professor in the Department of Energy at Aalborg University in Denmark. Henry Chung is Chair Professor of Electrical Engineering at City University of Hong Kong, China. Yuanbin He is Associate Professor in the School of Automation at Hangzhou Dianzi University in China. Min Huang is a Lecturer in the Department of Electrical Engineering at the Shanghai Maritime University in China.

• Author Biography xiiiPreface xviiPart I Background 11 Introduction 31.1 Architecture of DG Grid-Connected Converter 31.1.1 Power Conversion Stage 51.1.1.1 Switching Network 51.1.1.2 Output Filter 61.1.2 Control Stage 71.2 Challenges for Controlling DG Grid-Connected VSCs with High-Order Power Filter 81.2.1 Intrinsic Challenges 81.2.1.1 Filter Parametric Sensitivities 91.2.1.2 Digital Delay 101.2.2 Extrinsic Challenges 101.2.2.1 Grid Impedance Variation 101.2.2.2 Disturbances at the PCC 101.3 Methods for Controlling DG Grid-Connected VSCs with High-Order Power Filter 121.3.1 Methodologies to Assess the Stability of DG Grid-Connected VSCs 121.3.1.1 Eigenvalue-Based Analysis 121.3.1.2 Impedance-Based Stability Analysis 121.3.1.3 Application Issue Related to Impedance-Based Stability Analysis 131.3.2 Methods to Mitigate Filter Resonance 141.3.2.1 Online Grid Impedance Estimation 141.3.2.2 Inherent Damping 151.3.2.3 Passive Damping 151.3.2.4 Active Damping 171.3.2.5 Hybrid Damping 191.3.3 Harmonic distortion Mitigation Methods 201.4 Supplementary Note 21References 222 Control Structure and Modulation Techniques of Single-Phase Grid-Connected Inverter 292.1 Control Structure of Single-Phase Grid-Connected Inverter 292.1.1 Natural Frame Control 302.1.2 Synchronous Reference Frame Control 322.1.3 Grid Synchronization Methods 332.1.3.1 Zero-Crossing Method 332.1.3.2 Filtering of Grid Voltages 342.1.3.3 PLL Technique 342.2 Modulation Methods 352.2.1 Unipolar Modulation Method 352.2.1.1 Continuous Unipolar Modulation 362.2.1.2 Discontinuous Unipolar Modulation 362.2.2 Bipolar Modulation Method 392.3 Summary 40References 41Part II LCL/LLCL Power Filter 433 An LLCL Power Filter for Single-Phase Grid-Connected Inverter 453.1 Introduction 453.2 Principle of Traditional LCL Filter and Proposed LLCL Filter 463.3 Parametric Design of LCL and LLCL Filters 493.3.1 Constraints and Procedure of Power Filter Design 493.3.2 Saving Analysis on the Grid-Side Inductance 533.3.3 Specific Design Consideration for a Simple Passive Damping Strategy 533.4 Design Examples for LCL and LLCL filters 543.5 Experimental Results 563.5.1 Experimental Results 573.5.2 Analysis and Discussion 583.6 Summary 59References 594 Modeling and Suppressing Conducted Electromagnetic Interference Noise for LCL/LLCL-Filtered Single-Phase Transformerless Grid-Connected Inverter 614.1 Introduction 614.2 Conducted EMI Noise Analysis 624.2.1 CM and DM Voltage Noises 624.2.2 Spectrum of DM and CM Voltage Noise for GCI Using DUPWM 644.2.3 Spectrum of DM Voltage Noise for GCI Using BPWM 674.3 Modified LLCL Filter to Fully Suppress the Conducted EMI Noise for GCI Using DUPWM 684.3.1 Modified Solution for LLCL Filter 684.3.2 Improved Parameter Design of LLCL filter 724.3.3 Constraints on Harmonics of the Grid-Injected Current and EMI Noise Within 150 kHz to 1 MHz 724.3.3.1 Constraints on Leakage Current 734.3.4 Experimental Verification 744.3.4.1 Power Spectrum of the Grid-Injected Current 754.3.4.2 Measured Conducted EMI Noise 754.3.5 Negative Dc-rail Voltage with Respect to the Earth V Dc_n and Leakage Current 784.4 Novel DM EMI Suppressor for LLCL-Filtered GCI without CM Noise Issue 794.4.1 Proposed DM EMI Suppressor 794.4.2 Experimental Verification 834.5 Summary 854.5.1 For Single-Phase Transformerless GCI Using DUPWM 854.5.2 For Single-Phase Transformerless GCI Using BPWM or a System Without cm EMI Noise Issue 85References 86Part III Passive Damping 895 Design of Passive Damper for LCL/LLCL-Filtered Grid-Connected Inverter 915.1 Introduction 915.2 Design Method for Passive Damping 925.2.1 Passive Damping Scheme of LCL Filter 925.2.2 Passive Damping Scheme of LLCL Filter 955.2.3 Design Example 975.3 Analysis of Power Loss Caused by the Filter 985.3.1 Passive Damping Power Loss 985.3.2 Power Losses in Inductors 1005.4 Experimental Results 1015.5 Summary 110References 1136 Composite Passive Damping Scheme for LLCL-Filtered Grid-Connected Inverter 1156.1 Introduction 1156.2 Upper and Lower Limits of the PR + HC Controller Gain 1166.2.1 LLCL Filter-Based Grid-Connected Inverter Configuration 1166.2.2 Lower Limit of the PR + HC Controller Gain 1176.2.3 Upper Limit of the PR + HC Controller Gain 1186.3 E-Q-Factor-Based Passive Damping Design 1196.3.1 Principle of the Equivalent Q-Factor Method 1196.3.2 E-Q-Factor-Based RC Parallel Damping Design 1216.3.3 E-Q-Factor-Based RL Series Damping Design 1246.4 New Composite Passive Damping Scheme for the LLCL Filter 1266.4.1 Composite Passive Damping Scheme 1266.4.2 Design Example 1276.4.3 Analysis of Achieved Damping 1296.5 Experimental Verification 1346.6 Summary 136References 138Part IV Robust Control Design 1397 Robust Hybrid Damper Design for LCL/LLCL-Filtered Grid-Connected Inverter 1417.1 Introduction 1417.2 Control Bandwidth Analysis of the Grid-Current Feedback Method 1427.2.1 LCL/LLCL-Filtered Grid-Connected Inverter System 1427.2.2 Maximum Achieved Bandwidth of the Control Method 1437.3 Proposed Single-Loop Control with High Bandwidth 1457.3.1 Mathematical Model of the Proposed Single-Loop Control with Hybrid Damper 1457.3.2 System-Characteristics-Based Single-Loop Control Design Methodology 148Step 1: Design of the RC Parallel Damper 148Step 2: Design of the Proportionality Coefficient K p of the PR + HC Regulator 148Step 3: Determination of the Critical Grid Inductance 149Step 4: Determination of the Critical Frequency Region for Case 1 and the Critical Frequency (f 0 of Case 1 and f L0 of Case 2) 151Step 5: Design of the Digital Notch Filter 152Step 6: Checking the Phase Margin of the Entire System 1537.4 Design Example 1557.4.1 System Design 1557.4.2 System Parameter Robustness Analysis 1567.5 Experimental Verification 1567.6 Summary 160References 1618 Robust Impedance-Based Design of LLCL-Filtered Grid-Connected Inverter against the Wide Variation of Grid Reactance 1638.1 Introduction 1638.2 Modeling of the LLCL-Type Grid-Connected Inverter 1648.2.1 System Description 1648.2.2 Norton Equivalent Model 1658.3 Stability Analysis Considering Grid-Reactance Variation 1668.3.1 Non-Passive Regions of Inverter Output Admittance 1668.3.2 Possible Instability Under the Wide Variation of Grid Reactance 1678.4 Proposed Measures and Design Procedure Under the Grid-Reactance Variation Condition 1688.4.1 Proposed Measures Against Grid-Reactance Variation 1688.4.2 Design Procedure 170Step 1- Calculate the Minimum Grid Inductance L g_min 170Step 2- Design L 1 ,C total , and L 2 171Step 3- Design the Bypass Filtering Branch 172Step 4- Design the Minimum Grid Capacitance C g_min 172Step 5- Design the Proportional Gain K P of the PR+HC Regulator 172Step 6- Select C EMI ,C d , and R d 173Step 7- Check F I < F D 2 1758.5 Design Example 1778.6 Simulation and Experimental Verification 1798.6.1 Simulation 1798.6.2 Experiments 1828.6.2.1 Experimental Results 1838.6.2.2 Analysis and Discussion 1858.7 Summary 187References 187Part V Active Damping 1919 Active Damping of LLCL-Filter Resonance Based on LC-Trap Voltage or Current Feedback 1939.1 Introduction 1939.2 Control of LLCL-Filtered Grid Converter 1949.2.1 Description and General Control 1949.2.2 Block Diagrams of Different Active Dampers 1969.2.3 Effects of Delay G d (s) 1979.3 Circuit Equivalences of LLCL Active Dampers 1999.3.1 General Virtual Impedance Model 1999.3.2 LC-Trap Voltage Feedback 2009.3.3 LC-Trap Current Feedback 2049.4 Z-Domain Root-Locus Analysis 2069.4.1 Z-Domain Transfer Functions 2069.4.2 Root-Locus Analyses with Different Active Dampers 2079.4.3 Comparison 2099.5 Experimental Verification 2099.6 Summary 212References 21310 Enhancement of System Stability Using Active Cancelation to Eliminate the Effect of Grid Impedance on System Stability and Injected Power Quality of Grid-Connected Inverter 21710.1 Introduction 21710.2 Principle of the Grid Impedance Cancelator 21810.3 Modeling with the Grid Impedance Cancelator 22110.3.1 System Configuration with the Grid Impedance Cancelator 22110.3.2 AC Voltage Regulation 22210.3.3 Active Damping Function 22210.3.4 dc Capacitor Voltage Control 22610.4 Modeling of the Grid Impedance Cancelator 22610.5 Experimental Verification 23110.6 Summary 239References 239Index 241