Creepage and Clearance for MVDC Power Electronics Ryan Olson, Master’s Student University of Wisconsin – Milwaukee College of Engineering and Applied Sciences Department of Electrical Engineering

Overview With the emerging field of power electronics we aim to develop an integrated EMI characterization platform for new generations of power electronic converters using Wide Band Gap (WBG) power semiconductors for medium voltage systems. WBG devices will have a transformative impacts on power and energy delivery and management. Obtain higher switching frequency and device breakdown voltage capabilities Major challenges arise from the high voltage edge rates (dV/dt) and high electric field in these WBG converters which result in significant EMI spectral content in the 10-100MHz High frequency dV/dt is the source of baseplate displacement current into the ground chassis structure which will have an impact on partial discharge failures across the Multi-Chip Module (MCM) substrates, which is a major factor to achieving high power density modules. The challenges drive the need to increase the voltage dielectric stand-off distances and necessitates redefining creepage and clearance requirements Current creepage and clearance requirements were derived from low voltage AC systems and if improperly applied can lead to reduced reliability of equipment and potentially cancel out the benefits of WBG converters

Impact/Characterization of EMI Traditional IGBT-based systems have operational frequencies up to 50 kHz and content in the extended dynamics range. Which can be easily suppressed using lumped element analysis WBG systems operate at higher frequencies with extended dynamics range up to approximately 100 MHz. In this “Near-RF” range, lumped element analysis becomes inadequate, and changes how we look at EMI characterization, modeling, and mitigation High electric potentials on isolated heat sinks and high-frequency magnetic cores in the presence of high dv/dt induced displacement currents to equipment chassis Introduces coupling effects that can lead to “EMI-induced” degradation of equipment

Creepage and Clearance Shortest path between two conductive parts or between a conductive part and the bounding surface(enclosure) of the equipment Creepage is measured along the surface of the insulation Clearance is measured through air Other contributing factors: Pollution degrees (Dust, moisture, etc.) Insulation types

Electrical Discharges Electrical discharges is the localized dielectric breakdown under high voltage stress, which reduces the life expectancy of the system. There are two main types of Electrical discharge: Disruptive discharge - Gap between two conductors is fully bridged by discharge Partial Discharge - Does not bridge the space between two conductors Causes of Partial Discharge: Non-Homogenous Electric Field Defects in Insulation Presence of moisture or cracks Contamination on insulation surface Voltage exceeding dielectric strength of insulation Types of Partial Discharge: Internal – Due to cavities within the insulation External – Leakage current on surface of insulator Corona – Created by the presence of a sharp edge in the vicinity of a high voltage source

Surface Charge Measurement Physics based approach to understand the effects of partial discharge on the surface of the insulating material. What is causing the accumulation of charges? High dv/dt induced displacement currents to ground To understand the impacts of the displacement currents through equipment chassis we look into Common-Mode equivalent models

CM Model Methodology Process: Choose arbitrary point P Perform KVL/KCL of circuit Bring into state space Operate on equation with voltage/current transformation matrices Decompose the differential equations into MM (CM and DM) Extract the CM equation Create CM equivalent model Take the same process for different topologies and provide a way for interconnecting to form a system of power electronic systems.

Half-Bridge CM Model Method 1 Method 2

3-Phase Inverter CM Model DC Side AC Side CM Equivalent Circuit

Future Work After looking at several different power electronic power converters we want to implement what we have learned and apply to a system of power electronic converters. The proposed start to the Modular Multi-level Converter (MMC) is pictured below. Next steps are to bring models into PLECS, a simulation software, and validate displacement and other circulating currents in the system. Once validated we can run tests and begin defining the creepage and clearance requirements for MVDC power electronics.

Metamodel Development The creepage and clearance requirements can be seen as spatial allocations of Dielectric Stand-Off (pink) for the PEBB (right) and the MMC (previous slide) Our end goal is to take these spatial allocations for creepage and clearance requirements and produce Metamodel based scaling laws from a virtual prototyping process that takes into account the discrete building blocks associated with multi-cell based power conversion and distribution equipment. This approach is aimed at developing scalable modules for the Leading Edge Architecture for Prototyping Systems (LEAPS) database Which serves as a catalog of equipment for S3D Which is optimized to one of five selectable objectives within S3D: power density, specific power, efficiency, reliability, and specific cost