www.vicorpower.com POWER MODULES 15 www.power-mag.com Issue 1 2025 Power Electronics Europe selection for these installations was strongly dependent on the quality of visible light. This is because, as light passes through the atmosphere, it is subject to a disturbance known as a wavefront aberration. Using Microgate technology, the captured light is reflected from the primary to a secondary, adaptive mirror, which is physically deformed to re-establish what is known as a “plane” wavefront. In the case of the ESO-ELT project, Microgate delivers all of the real-time control hardware and software to mechanically deform the mirror and physically manipulate the incoming wavefront to correct for these atmospheric disturbances and improve the image quality. The ability to control the mirror’s geometric shape requires the use of contactless, linear voice-coil motors that conceptually are similar to a loudspeaker (see a short video demonstration). The adaptive mirror is 2.4 meters in diameter and is made of highly specialized glass with a thickness of 1.9 millimeters. The voice-coil motors are driven by a precise current driver and a series of colocated permanent magnets. These are glued to the back of the mirror and provide the force to deform the glass. This process is performed across the entire surface of the adaptive using 5,316 motors, each with an inter-axis distance, or pitch, of about 30 millimeters. The adaptive mirror physically floats on the magnetic field generated by the voicecoil motors. Each coil allows a dedicated control current to locally deform the mirror and correct the shape. This is achieved by using an equivalent number of highlysensitive capacitive, or position, sensors with an accuracy in the nanometer (millionth of a millimeter) range. Using electronics operating at a frequency of about 100 kHz, Microgate engineers can completely redefine the shape of the mirror in one millisecond. Once the gap has been measured, FPGA-based processors apply the correct commands to the mirror in real time and bring the control error to zero. The result is an extremely sharp and clean image that is rendered without having to launch a telescope into space. “The process requires extreme precision to correct the wavefront aberrations,” said Gerald Angerer, Microgate hardware development engineer. “As a result, we can improve the image resolution significantly.” High density power modules are mission critcal to honing adaptive optics The energy challenges to achieve such precision are considerable. For example, accurate thermal management of the adaptive optics system is critical and requires all exposed surfaces to be kept close to ambient temperature to avoid local turbulence. To compensate, Microgate uses a direct-expansion gas cooling system to thermally dissipate the motor-control electronics. Other cooling materials, such as water or glycol have been excluded, because even a small loss of coolant on the primary mirror could cause catastrophic damage to the entire telescope. The power challenge is made even more difficult by the limited space available for any power delivery solution, given the constraints imposed by housing thousands of motors in a confined space. A previous option required remote DC-DC converters to bring power to the motors with relatively long and complex wiring. To streamline the approach, Microgate chose the Vicor DCM3623 series DC-DC power module. The power-system board is now mounted on the underside of the gas-cooled cold plate, and each DCM3623 powers up to 36 motor channels, eliminating complicated wiring. “Vicor’s high-efficiency and high-power density modules are very compact and reliable and take up very little space on the circuit board,” said Angerer. “These miniaturized power converters are the best option for us. We have been using them for more than 10 years and there is currently no comparable substitute.” Vicor power modules deliver other benefits over alternative solutions: Power density: Vicor power modules are compact and extremely dense to meet the intense power demands of the ELT mirrors in a very confined space. Efficiency: The modules reduce energy losses created in the form of heat, helping to keep the temperature of the optical system stable. Too much heat could potentially degrade performance or distort optics. Fast transient response: The output voltage of Vicor modules remains stable within a wide frequency band, ensuring precise motor operation even under fast step-load variations. Figure 3: The secondary or adaptive mirror is made of highly specialized glass with a thickness of about 1.9 millimeters. The copper coils represent the linear motors. Figure 4: Microgate uses the Vicor DCM3623 seriea DC-DC power module to mechanically deform the miror and physically manipulate the incoming wave=front to correct for these atmospheric disturbances. This process is mission criticalto the telescopes optics to produce stronger light and ultimately higher image quality.
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