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TB 699 2017 Control methodologies for direct voltage and power flow in a meshed HVDC grid

This brochure provides the requirements and the classification of different control methods, including the coordinated system control, in order to ensure system security and efficient operation of the combined AC and HVDC system in an electricity market environment. In addition, a range of power flow controlling devices is described for efficient utilization of overhead lines and cables in the HVDC grid. The main focus for the technical brochure is on static control characteristics.

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TABLE OF CONTENTS

 1. INTRODUCTION

   1.1 BACKGROUND

   1.2 POWER FLOW CONTROL AND DIRECT VOLTAGE CONTROL

2. POWER FLOW CONTROL IN A POINT-TO-POINT TRANSMISSION LINK

   2.1 INTRODUCTION

   2.2 HVDC POINT-TO-POINT SCHEMES

      2.2.1 DC Current Control in a Point-to-Point Scheme

      2.2.2 The Compounding Point

   2.3 LCC CONVERTERS

      2.3.1 Converter Control Parameters

      2.3.2 Rectifier Control Methods

      2.3.3 Inverter Control Methods

      2.3.4 Selection of Appropriate Control Methods

   2.4 VSC CONVERTERS

   2.5 HVDC AUXILIARY CONTROL FUNCTIONS

      2.5.1 Frequency Control

      2.5.2 Power Oscillation Damping

      2.5.3 Emergency Power Control

   2.6 CONCLUSION

3. CONTROL REQUIREMENTS IN A MESHED HVDC GRID

   3.1 INTRODUCTION

   3.2 CONTROL REQUIREMENTS

      3.2.1 Control the Energy Balance and Share the Power Imbalance between Several Converters

      3.2.2 Have no Risk of Hunting between Different Converters Sharing Power Imbalance

      3.2.3 Keep the DC Voltage between Upper and Lower Voltage Limits

      3.2.4 Track the Set-points and Ensure the Possibility to Dispatch and Schedule 3.2.5 Be Interoperable and Easy to Implement

      3.2.6 Prevent Overload

      3.2.7 Work Together with Power Oscillation Damping and Emergency Control

      3.2.8 Ensure Interoperability with Power Controlling and Frequency Controlling Stations

      3.2.9 Have a Stable Performance

      3.2.10 Reliable Operation without Telecommunication System

      3.2.11 Redundancy / Diverse Redundancy Provision

   3.3 CENTRAL AND LOCAL CONTROL

      3.3.1 Definitions

   3.4 REFERENCES

4. NODE VOLTAGE CONTROL AND POWER BALANCING

   4.1 INTRODUCTION

   4.2 BASIC CONTROL PRINCIPLES

      4.2.1 Current Based Control

      4.2.2 Power Based Control

      4.2.3 Converter and System Limits

   4.3 BASIC CONVERTER CONTROL STRATEGIES

      4.3.1 Voltage Droop Control (Positive Droop Constant)

      4.3.2 Constant Flow Control (Infinite Droop Constant)

      4.3.3 Constant Voltage Control (Zero Droop Constant)

   4.4 ADVANCED CONVERTER CONTROL STRATEGIES

      4.4.1 Voltage Margin Control

      4.4.2 Dead-Band Droop Control

      4.4.3 Undead-Band Droop Control

   4.5 BASIC GRID CONTROL STRATEGIES

      4.5.1 Centralised Voltage Control

      4.5.2 Distributed Voltage Control

   4.6 ADVANCED GRID CONTROL STRATEGIES

      4.6.1 Centralised Voltage Control with Centralised Back-Up

      4.6.2 Centralised Voltage Control with Distributed Back-Up

      4.6.3 Distributed Voltage Control with Distributed Back-Up

   4.7 CONCLUSION

   4.8 REFERENCES

5. POWER FLOW CONTROLLING DEVICES FOR HVDC GRIDS

   5.1 INTRODUCTION

   5.2 SWITCHABLE SERIES RESISTORS

      5.2.1 Mechanical Devices

      5.2.2 Semiconductor Based Devices

   5.3 DC/DC CONVERTER

      5.3.1 Basic Topology and Loss Considerations

      5.3.2 Bipolar DC/DC Converter

      5.3.3 Simplified Converter Model

   5.4 OTHER TECHNOLOGIES FOR DC LINE POWER FLOW CONTROL

      5.4.1 Current Flow Controller

      5.4.2 Dual Active Bridge (DAB) DC/DC

      5.4.3 Transformerless LCL DC/DC Converter

   5.5 CONCLUSION

   5.6 REFERENCES

 6. COORDINATED SYSTEM CONTROL, POWER FLOW CALCULATION AND COMMUNICATION

   6.1 PURPOSE OF COORDINATED SYSTEM CONTROL

   6.2 DATA ACQUISITION RELATED TO THE COORDINATED SYSTEM CONTROL

      6.2.1 Controlled Variables

      6.2.2 Observed Variables

   6.3 COORDINATION OF SET -POINTS AND CONTROLLER PARAMETERS

      6.3.1 Change of Set-Points

      6.3.2 Transition from One Node Voltage Control Strategy to Another

      6.3.3 Change of Converter Control Parameters

      6.3.4 Startup and Shutdown Procedures

      6.3.5 Runup and Runback Controls

   6.4 POWER FLOW ANALYSIS

      6.4.1 Standard DC System Power Flow

      6.4.2 Power Flow, With Droop

      6.4.3 Power Flow, With Power Sharing

      6.4.4 Power Flow, with DC/DC converter

      6.4.5 AC/DC Power Flow

      6.4.6 Optimal Power Flow Calculation

   6.5 RELIABILITY

      6.5.1 Uncertainty in Scheduled Power Transmission

      6.5.2 Real-time Evaluation of System Security

   6.6 COMMUN ICATION

      6.6.1 Communication Speed Requirements

      6.6.2 Communication Infrastructure

      6.6.3 Telecommunication Protocols

   6.7 CONCLUSION

   6.8 REFERENCES

7. CONCLUSIONS

8. APPENDIX A. DC/DC CONVERTER CONTROL OPTIONS

9. APPENDIX B. DC/DC CONVERTER SIMULATION

10. APPENDIX C. ADDITIONAL INFORMATION