IEC 62751-2:2014

Overview

IEC 62751-2:2014 is an international standard established by the International Electrotechnical Commission (IEC) that specifies the detailed methodology for calculating power losses in voltage sourced converter (VSC) valves used in high-voltage direct current (HVDC) systems. Focusing specifically on modular multilevel converters (MMC), this standard covers the design where each valve consists of multiple self-contained, two-terminal controllable voltage sources connected in series.

This part of the standard is crucial for electrical engineers and system designers involved in HVDC converter development, as it provides standardized formulas and guidance to accurately estimate losses in MMC valves. Power loss estimation is essential for improving efficiency, thermal management, and reliability in HVDC transmission technology.

Key Topics

• Scope of Application IEC 62751-2 applies to MMC valves where each modular cell incorporates either a single turn-off semiconductor device or multiple such devices in series, also known as the cascaded two-level converter topology. It includes half-bridge configurations and offers guidance on extending calculations to alternative MMC building blocks.

• Loss Categories and Calculation Method The standard breaks down valve losses into conduction losses, switching losses, DC voltage-dependent losses, capacitor losses, snubber circuit losses, and valve electronics power consumption. It presents comprehensive formulas for calculating each type, accounting for semiconductor device characteristics, operating parameters, and converter station data.

• Operating Conditions and Parameters Input data requirements include valve and simulation data, device characteristics, converter operating conditions, and system voltage and currents. These input parameters are vital for accurate numerical simulations and loss estimation.

• Detailed Analysis and Guidance Annexes provide extensive explanations of power loss mechanisms, including conduction path modeling, switching event analysis, and the impact of voltage and current phase relationships. Additionally, recommendations for loss calculation reporting documentation are included, ensuring consistency and clarity in engineering assessments.

Applications

• HVDC Transmission Systems The standard is fundamental for designing and optimizing MMC-based HVDC converters, which are widely used for long-distance power transmission and interconnecting asynchronous grids.

• Power Electronics and Semiconductor Device Engineering Semiconductor manufacturers and power electronics engineers utilize the guidelines to evaluate device performance, loss reduction techniques, and thermal management strategies.

• Converter Station Design and Operation Accurate loss calculations help in planning cooling systems, selecting components, and improving overall converter station efficiency and reliability.

• Renewable Energy Integration As MMCs are commonly used in connecting large-scale renewable energy sources like offshore wind farms to grids, this standard assists in assessing losses and operational costs.

Related Standards

• IEC 62751-1 - Power losses in VSC valves for HVDC systems – Part 1: Two-level converters: Complements Part 2 by addressing two-level converter topologies.

• IEC 61850 - Communication networks and systems for power utility automation: Relevant for integrating MMC valve monitoring and control systems.

• IEC 60947 - Low-voltage switchgear and control gear: Offers foundational semiconductor device specifications referenced in HVDC component analysis.

• IEEE Standards on HVDC and Power Electronics - Complement IEC 62751-2 by providing additional guidelines on converter operation and semiconductor device testing.

Keywords: IEC 62751-2, HVDC systems, voltage sourced converter, VSC, modular multilevel converter, MMC, power loss calculation, semiconductor devices, conduction losses, switching losses, high-voltage direct current, valve losses, cascaded two-level converter, power electronics standards, electrical engineering, HVDC converter design.