Application of VSC HVDC in a System Black Start Restoration

Introduction

The use of synchronous generators is typical for BSR. However, HVDC transmission, where available, is proving to be an attractive asset. Voltage Source Converter (VSC) HVDC transmission is being introduced to reinforce the existing AC interconnected grid, create new long-distance interconnections, connect asynchronous grids, and integrate large amounts of renewable generation. VSC HVDC has demonstrated the ability to support BSR due to its flexibility; however, there have not been any general guidelines to describe such functionality. The objective of this Technical Brochure (TB) is to provide a comprehensive analysis of the black start procedure using VSC HVDC system for power system stakeholders as an alternative option. This TB addresses the following key topics:

• Identify the capabilities and limitations of VSC HVDC in the BSR.
• Define general specifications and design requirements for BSR with VSC HVDC.
• Electromagnetic Transient (EMT) and real-time simulation (RTS) modeling requirements for BSR with VSC HVDC. This is to verify the VSC control and protection functionality during BSR.
• Identify the potential interaction between VSC HVDC and the AC network during a BSR and between VSC HVDC and the source of energy driving the BSR.
• A case study to demonstrate the feasibility of renewable resources, i.e. offshore wind farm, for BSR.

Review of black start restoration procedure

First chapter provides a definition of black start unit as well as its requirements, and describes typical steps considered to prepare the power system for BSR. This includes predefining black start paths and grid segmentation which can be verified in advance through steady state and dynamic simulation studies. Although the amount of load pick up can vary for each network, it is important to select the amount of load pick up to maintain system stability during the restoration. In addition, an overview of different BSR approaches such as top-down, bottom-up or hybrid approaches are discussed. Regardless of which restoration approach is used, Transmission System Operator (TSO) is obligated to prepare the detailed restoration plan in advance. Finally, a brief description of recent power system blackouts is presented.

Role of HVDC technology in black start restoration

This chapter describes the role of HVDC technology in BSR. First, both Line Commutated Converter (LCC) and VSC technology are compared for BSR applications. LCC technology cannot be considered as a black start unit because it cannot control the voltage and frequency directly; however, it can support during the restoration process after the system voltage and frequency are established and the restored system has sufficient strength to allow for LCC to operate stably. Therefore, this TB focuses on applications of VSC for system restoration. Two most common VSC’s control strategies, grid following (GFL) and grid forming (GFM), are briefly described considering their advantages and challenges. In this TB, GFM control mode can control both voltage and frequency independently without being dependent upon an external grid for synchronization. Therefore, it is the choice for BSR applications. Furthermore, general BSR sequencing using VSC has been explained. Finally, examples of using VSC for BSR have been presented.

Specification and design requirements for black start restoration with VSC HVDC

It is understood that each HVDC project needs specific design requirements; however, this chapter provides a general specification and design consideration that can be evaluated. This chapter describes the importance of “healthy” end of HVDC link to provide sufficient source of energy for a successful BSR. Additional key considerations such as converter ratings, converter transformer design, DC system energization, auxiliary...