SY-EPC-LPC Converters Concepts

Introduction

Context

Introduction

This page describes some key concepts our original designs are based on. It will clarify some choices, strongly linked to the very specific environement: CERN accelerator complex converters.

Context

Power Converters are generally using air or water for cooling, and only these cooling types will be presented. All solutions described in these pages are specific to modular power modules. Water cooled converters are usually designed as easy plug-in modules (quick-fit connectors, for fast exchange), under relative standard demineralyzed water environment. Lifetime issues are reliability are a key concern, and often determines technical choices.

Usual Materials Usual Materials

Material	Caracteristicsnbsp;@25°C, P_atm
Material	Density [kg.m^-3]	Heat capacity [J.kg^-1.K^-1]	Heat conductivity [W.m^-1.K^-1]
Air	1.2	1000	0.024
Water_liquid	1000	4185	0.58
Copper	8940	385	400
Aluminium	2700	897	200
Inox	8000	450	16

Table of the main material being used in cooling calculations

This table shows copper is a very good material to tranfer heat. Aluminum, being 3 times lighter than copper transmits heat correctly also, and is then often used for optimized weight/performance heatsinks. Storing heat in a given volume of copper is only 1.3 better than in aluminium (at a 3x wight cost). Noticeable difference remains nevertheless the capability (conductivity) the copper vill propose to diffuse heat in the volume, especially if heat is not uniformly transferred to the volume (case of a high density power semiconductor on a oversized heatsink)

Heat Capacity Heat Capacity

Heat capacity (chaleur massique) defines the energy required to elevate the temperature of a body. It depends strongly on the material type. This property is often used in CERN crowbar design, to quickly removed magnet stored electical energy to heat stored energy, through an external resistor. Heat capacity usually deals with Energy [Joules].

Formula: heat capacity formula .xlsx

Heat Transfer Modes Heat Transfer Modes

Thermal design is based on 3 different heat transfer modes: conduction mode, convection mode, or radiated mode. (conduction and convection modes are sometimes grouped). It is likely that all 3 modes will co-exist generally. Transfer mode usually deals with Power [Watts].

Conduction Mode

Conduction can only take place within an object or material, or between two objects that are in direct or indirect contact with each other. Transfer of heat energy by microscopic diffusion and collisions of particles or quasi-particles within a body due to a temperature gradient.

Convection Mode

Convection mode deals with a transmission mode where a part is a moving fluid moving (liquid or gaz). A forced convection mode uses an external system (fan) to increase the movement of the fluid.
A very simple formula is:

Formula: Newton law .xlsx

Formula which required the knowledge of the transfer coefficient of the fluid

Fluid	Transfer Type
Fluid	Natural Convection	Forced Convection
Air Transfer Coefficient h [W.m^-2.K^-1]	5..50	10..500
Water Transfer Coefficient h [W.m^-2.K^-1]	100..1000	100..15 000

Overview of the transfer coefficient fow air and water

Radiated Mode

Energy can also be transmitted to ambient air being irradiated (very efficient at high temperature).

Formula: Stefan law .xlsx

Modeling Modeling

Some typical modeling cases are discussed below

Semiconductor and its heatsink

Formula: Stefan law .xlsx .edms