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A highly efficient intelligent industrial microwave heating system based on high power solid state technology

Periodic Reporting for period 2 - CLEAN-HEAT (A highly efficient intelligent industrial microwave heating system based on high power solid state technology)

Reporting period: 2016-06-01 to 2017-08-31

CLEAN-HEAT was a 24-month project funded by the European Commission’s H2020 framework programme within the SME instrument phase 2 funding scheme.

The CLEAN-HEAT consortium consisted of the lead SME, Fricke and Mallah Microwave Technology GmbH (F&M) partnering with another SME, Microwave Technology (MTL). These SME partners were supported by a number of third parties including Pera Technology Solutions Ltd and London Metropolitan University (LMU).

Magnetrons are the most widely used microwave technology today for both industrial and domestic microwaves. But these systems can only achieve efficiencies of around 45 to 50%, pose safety risks as the use high voltages (5kV) and the magnetrons have a short lifespan requiring frequent replacement. Magnetron technology does not allow for the automatic adjustment of power level to match the load variations. These limitations have a huge cost to industrial microwave processes and there are calls for more efficient solutions. Across Europe, microwaves consume over 9.6 TWh of electrical energy annually.

F&M wanted to upscale its 200W solid-state continuous wave microwave system to address these limitations. The 1kW Gallium Nitride (GaN) based microwave system was expected to save at least 25% on electricity consumption, operate at more than 70% efficiency, allow automatic adjustment of power level in response to load variations and significantly reduce equipment size. Also of importance was increased lifespan to eliminate the need for frequent and costly replacements. With all these excellent features and performance advantages, our product needed to be cost competitive with magnetron based microwave sources.

Solid-state microwave technology has many applications including moisture meters, medical RF-Surgery, and domestic and industrial heat processing. It also offers opportunity for automatic power matching that enhances energy efficiency and faster processing speeds than conventional magnetron systems. Full adoption of our technology in both domestic and industrial microwave ovens would lead to potential energy savings of 6.74TWh of electrical power across Europe.
During the first 12-months of the project all subsystems that make up the CLEAN-HEAT microwave system were specified and designed. The solid-state power amplifier (SSPA) was designed and its performance optimized using simulation tools, before it was manufactured. The SSPA performance was measured to validate the design. SSPA design included (i) characterization of the selected GaN devices; (ii) design of the RF amplifier and power circuitry; (iii) specification and characterization of the selected high-power isolator; (iv) design, simulation and test of the power divider and combiner; and (v) design and test low loss RF coupler and detector circuits for measuring forward and reverse power.

A thermal management and control system for the GaN-SSPA was designed and developed. This included the development of an effective cooling system. The cooling system has been integrated inside the mechanical housing of the 1kW GaN-SSPA microwave source. The 1 kW GaN-SSPA was RF tested under continuous wave mode conditions. Liquid thermal management system functioned as expected to dissipate excess heat generated by the SSPA module. It was verified the case temperature of the SSPA was maintained at 25.5°C.

An innovative cross polarizing (CP) cavity was designed, simulated and optimized to obtain the required cross polarized RF signal. The CP cavity was optimized to ensure maximum energy is contained within the microwave chamber and that the electromagnetic field is distributed evenly inside the chamber to ensure homogeneous heating of the target material within the chamber. The effectiveness in terms of uniform heating distribution and drying/heating rate of the CP cavity was verified through measurements and benchmarked against conventional microwave chambers.
Specifications for the power management system (PMS) for the proposed 1kW GaN-SSPA microwave source were evaluated and compared with the existing 200W SSPA based on LDMOS based amplifiers. Based on this analysis, a PMS using a decentralized system of power management circuits supported by temperature sensors were specified and designed.

The next 12-months of the project the project partners focused on integrating the 1kW GaN-SSPA the power management system, thermal management and control systems. The 1kW GaN-SSPA microwave source was then integrated with the CP cavity. The complete system was tested under extreme end-user conditions to demonstrate it functioned properly under continuous wave mode. The 1 kW GaN-SSPA source had an efficiency of 70% and delivered 1050 Watts of RF power at 2.45 GHz. The microwave system comprising emitter & PMS has efficiency greater than 80%. The system was subjected to different dielectric loads and compared with an equivalent conventional magnetron-based microwave system to show the effectiveness of CP cavity’s heating/drying rate over conventional microwave chamber. These results clearly indicate the effectiveness of the CP cavity in heating takes significantly shorter time, which is conducive to reduction in energy and CO2 emissions. The 1kW GaN-SSPA microwave source has been validated.

The outcomes of the CLEAN-HEAT project were disseminated through various online media, trade exhibitions, to our existing and potential clientele, and through presentations at various conferences. The 1 kW GaN-SSPA microwave source is a fully functional product ready for commercial exploitation.
We have developed a highly efficient and fully functional 1kW Gallium Nitride (GaN) solid-state power amplifier (SSPA) microwave source for continuous wave mode operation, which is a first and makes us market leaders. The system includes a power management, thermal management and control systems. Also developed is a circularly polarized (CP) cavity that provides homogeneous heating inside the microwave chamber. The 1kW GaN-SSPA microwave source has an efficiency of 70% and delivers 1050 Watts of RF power at 2.45 GHz. Compared to conventional microwave chambers the CP cavity takes significantly shorter time for heating. Both the 1 kW microwave source and CP cavity are conducive to reduction in energy and CO2 emissions. Compared to existing magnetron technology the GaN-SSPA microwave system has the following attributes: (i) higher efficiency; (ii) uniform heating; (iii) significantly longer lifespan; and (ii) requiring very low voltage (50 V) unlike magnetron technology which requires 5,000 V.

CLEAN-HEAT offers a completely new solution to industrial microwave users who suffer problems with high energy and O&M costs accruing from inefficiency of magnetron technology and its need for frequent replacements. Furthermore, our solid-state microwave technology is transferable to domestic microwaves and RF wireless systems further reducing energy consumption for domestic consumers and indirectly reducing the CO2 emissions from Europe’s power generating plants.

Our projections show that full adoption of our technology in both domestic and industrial microwave ovens could save up to 6.74 TWh of electrical energy representing a reduction of ca. 5.9 million tons of CO2 emissions from power generating plants. Such savings will significantly contribute towards the European Union target for a 20% cut in annual primary energy consumption by 2020.
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