Marco Bassani

In modern particle physics experiments, various electronic devices are frequently required to operate within noble liquids at cryogenic temperatures. Within the framework of the Deep Underground Neutrino Experiment (DUNE), a need has arisen to develop a DC-DC boost converter with an analog feedback loop control composed of discrete components, all capable of functioning at cryogenic temperatures. Consequently, Operational Amplifiers (OpAmps) must also be adapted to meet these requirements. However, there is no existing literature on off-the-shelf OpAmps with the required characteristics for cryogenic temperatures, nor on circuit-ready measurement setups applicable for obtaining these characteristics for the selected OpAmps. For this reason, this paper explores a measurement setup solution for cryogenic temperatures and the characterization of two operational amplifiers suitable for the analog control scheme. Due to application requirements, the quiescent current, offset voltage, offset input current, bias input current, open-loop voltage gain, and gain at 10 kHz or 100 kHz have been measured in function of the temperature, from 123 K to 333 K, and directly inside a liquid nitrogen (LN2) detector. Furthermore, this work required studying the thermocouple effect introduced at the interface between LN2 and air, which must be considered for the calculation of the desired OpAmp characteristic values. Finally, the measurement uncertainty has been evaluated and presented in this paper.

This work presents a technique to actively reduce the vibrations generated by magnetic anisotropy in sinusoidal brushless motors through current injection. These vibrations are an unwanted phenomenon mainly generated by the interaction between the rotor magnets and the stator teeth. These produce vibrations which are then transmitted to the frame and other mechanical parts such as bearings, gearboxes, transmissions, and joints, thus reducing the life, performance, and reliability of these components. First, different design strategies and control algorithms to passively and actively attenuate the vibrations are reviewed. Then, a narrowband active method that attenuates a harmonic vibration through the injection of a harmonic current is presented. The effectiveness of the proposed method was demonstrated on a prototype of a Surface Permanent Magnet Synchronous Motor (SPMSM). For the motor under test, an attenuation of −13.5 dB at 650 rpm and −29 dB at 800 rpm was achieved on the main frequency component, caused by the magnetic anisotropy, which in turn corresponds to the 72nd harmonic of the rotor mechanical speed.

Parallelization of power electronic converter units is a way to meet the high current requirements of modern electrification applications. In case of voltage source converters, parallel operation can be attained only if the voltages of all the units are equal. In the current state of the art, this voltage synchronization can be achieved at the fundamental frequency, but not at modulation frequency, hence requiring bulky filters to limit circulating currents; this lowers the system performance in terms of cost, volume, weight and sustainability. In this paper, the authors propose a novel approach to synchronization, acting directly at the modulation frequency level, thus removing the need for any filter. This technique relies on the natural parasitic inductance and resistance of the wiring among parallel units. Specifically, this paper presents the first of two synchronization stages required to reach the sub-nanosecond synchronization necessary to completely remove the filters. At start-up, a low-bandwidth industrial communication line, based on the CAN protocol, is exploited to guarantee that the error in the synchronization of PWM signals among all the parallel units is lower than 0.1%. This limits the initial circulating current, supporting the subsequent control stage that achieves sub-nanosecond synchronization. The proposed concept is validated by experiments using a commercial MCU unit with an unadorned CAN peripheral.