Compact 8kV Class High Voltage Planar Transformer for Electronic Power Conditioning Units

Space Segment - Payload

Status

Completed
Status date

2024-12-22
Activity Code

5C.382

Objectives

The objective of this activity is to design and develop a high voltage power transformer in planar technology for Electronic Power Conditioning Units (EPC) used to drive travelling wave tubes.

The aim is to develop a novel transformer design solution not existing today in Europe for up to 8kV class of EPCs (with research of margin up to 10kV).

A transformer engineering model is designed, manufactured and tested in a representative environment to validate the developed concept for space application.

The main intermediate objectives of this project are:

To establish a detailed requirement specification for the high voltage planar transformer,
To define a program (in Excel), based on the build-up in order to compute the tracks size of primary and secondary windings, the leakage inductance, the copper losses of the secondary and primary windings, the core losses, the resonant push-pull losses and rectifier losses,
To define thermal and electrical models of the High Voltage Planar technology,
To review and de-risk the available technologies and processes available in accordance with the technical requirements defined,
To minimise the manufacturing complexity and to ease flexibility during production aiming at a short time to delivery.

Challenges

The main technological challenges are the management of the high electrical fields inside the planar transformer assembly, and the thermal management of the transformer.

The chosen design needs to manage high voltage design rules in PCBs, while at the same time using a more complex build-up than high voltage PCBs currently used.

Thermal design needs to be optimized by using innovating solutions such as optimizing the transformer build-up and improving thermal interfaces with the structure.

Benefits

The main targeted improvements by using this new technology are:

EPC size reduction by 10%,
Complexity and part count reduction by 30%.

The development approach is to consider a flexible and scalable approach, to easily tailor specific application driven transformer demands (voltages/number of collectors) from a generic design.

The other expected benefits are:

Better process reproducibility,
No use of complex manufacturing processes (no potting required),
Decrease of the number of tools used during the manufacturing,
Decrease of the manufacturing lead time.

Features

Output-to-Input/structure isolation: superior to 8kV.

Maximum Peak common mode voltage: 10kV.

Voltage/Power level: scalable.

Conversion Power: at least up to 300W RF power (per channel continuous operation).

Output Flexibility: +/- (50V, 100V).

Maximum Output Current: 350mA.

Magnetic flux: max 0.2 Tesla.

EPC size reduction: -10%.

Complexity and/or part count reduction: -30%.

Thermal interface of EPC: operating temperature min/max: -20°C / +70°C / Startup temperature: -40°C.

Pressure range: vacuum & ambient pressure (baseline to cover partial pressure range, ambient pressure operation shall be possible for ground testing). Full critical pressure range can be assessed as an opportunity.

Partial discharges: max 5pC.

Lifetime: > 18 years (typical GEO telecom applications).

Compact 8kV product features

System Architecture

Resonant transformer topology working at high frequency.

The Planar transformer technology is based on a high voltage multilayer PCB equipped with its ferrites, thermal conductive material and mechanical fixations.

The secondary side is a single or multiple windings and the primary side is a push-pull type so double windings with a common point.

Plan

The project’s work plan is based on the following methodology:

Based on the state of the art of the Travelling Wave Tube Amplifier, to build the definition of a detailed technical requirement specifications for planar transformer,
To study suitable technologies to achieve a high voltage transformer in planar technology based on a technical trade-off and specific de-risking evaluation activities as High Voltage withstanding aspect,
To study and optimize the electrical and thermal concept of such technological assembly. This step includes detailed calculation and optimization of magnetics tools (including software calculation tools),
After the manufacturing of an Engineering Model (Elegant Bread Board - EBB), to test the High Voltage Planar technology in a realistic EPC environment. The tests sequence includes a Thermal Vacuum test sequence covering GEO mission needs.

Current status

The main achievements are:

In the frame of the project Requirements Review (RR):

The feasibility study to address the technology to the following TWT tubes has been validated: 150W Ku, 40W Q, 250W Ka, 170W Ka, 300W Ku, 150W C, 75W C, Dual 70W Ka and Compact Dual Ka/Ku TWT’s (80W RF) and for multi-tube constellations market,
The confirmation of implementation feasibility has also been successfully performed ; this study included the following tasks: definition of the preliminary mechanical architecture of the technical solution, planar losses optimization, PCB build-up, preliminary thermal analysis and preliminary electrical fields analysis.

In the frame of the project Technical Design Review (TDR):

Several electrical optimizations have been performed including parasitic capacitors computations and leakage inductance distribution,
Based on these optimizations, the development of the Planar/PCB build-up has been pushed including thermal and Electrical field analysis,
The derisking of the PCB technologies including incoming tests definition, High Voltage ageing behavior (with the definition of a specially dedicated representative test vehicle) and materials performances such as outgassing tests and dielectric strength.

In the frame of the project Preliminary Design Review (PDR):

The definition of the Elegant Breadboard (EBB) ; designed taking into account the challenge to establish a compromise between high voltage insulation properties and sufficient thermal drain capabilities of the HV planar transformer technology studied in the frame of this project. The demonstrator definition was based on Quadral EPC adapted to the selected TWT’s, i.e. 170W Ka. Detailed calculation and optimization methods for magnetic, electrical and thermal designs have been performed. The design took into account manufacturing and assembly properties in order to minimize the manufacturing complexity and to ease flexibility during production aiming at a short time to delivery.

In the frame of the project Final Review (FR) :

The planar transformer technology has been exposed to space representative environment. After a first step covering the ground test sequence, a TVAC sequence of 130 thermal cycles has been successfully performed in order to verify the high voltage design and environment effect (including the effect of the local increase of pressure). 10 cold starts at -40°C have also been performed. The test has then been pursued with success with a HV life test at +70°C base plate in order to reach a total test duration of 1500 hours. The test sequence also included thermal characterization under vacuum in order to validate the thermal model related to the evaluated technology.