Voltage Control of Multiphase Cage Induction Generators at a Speed Varying over a Wide Range

The subject of this publication is a method of controlling the DC voltage of a PWM rectifier supplied by a multiphase cage induction generator with the number of stator phases greater than three operating in a wide range of driving speeds. Voltage regulation is performed by changing the frequency and amplitude of the stator voltages with simultaneous switching of the phase sequence of these voltages. The step change of the voltage sequence is made in the designated ranges of the generator speed, which enables the stabilization of the output voltage in a wide range from the minimum speed of about 25% of the rated speed. Such sequence switching changes the number of pole pairs produced by the winding for each supply sequence. The difference compared to multi-speed induction machines is that, in the presented solution, there is only one winding, not a few, which enables good use of the machine’s magnetic core in the same dimensions as for the three-phase machine of a similar power. Steady-state characteristics and dynamic operation were obtained using laboratory measurements of a standalone nine-phase induction generator. The automatic control system maintained the output voltage at the set level, regardless of the generator load and driving power.

On-chip silicon photonic controllable 2 × 2 four-mode waveguide switch

Multimode optical switch is a key component of mode division multiplexing in modern high-speed optical signal processing. In this paper, we introduce for the first time a novel 2 × 2 multimode switch design and demonstrate in the proof-of-concept. The device composes of four Y-multijunctions and 2 × 2 multimode interference coupler using silicon-on-insulator material with four controllable phase shifters. The shifters operate using thermo-optic effects utilizing Ti heaters enabling simultaneous switching of the optical signal between the output ports on four quasi-transverse electric modes with the electric power consumption is in order of 22.5 mW and the switching time is 5.4 µs. The multimode switch exhibits a low insertion loss and a low crosstalk below − 3 dB and − 19 dB, respectively, in 50 nm bandwidth in the third telecom window from 1525 to 1575 nm. With a compact footprint of 10 µm × 960 µm, this device exhibits a relatively large width tolerance of ± 20 nm and a height tolerance of ± 10 nm. Furthermore, the conceptual principle of the proposed multimode switch can be reconfigurable and scalable in multifunctional on-chip mode-division multiplexing optical interconnects.

Time-Varying Kelvin Wake Model and Microwave Velocity Observation

In the synthetic aperture radar (SAR) imaging of ship-induced wakes, it is difficult to obtain the Doppler velocity of a Kelvin wake due to the lack of time-varying wake models and suitable radar equipment. The conventional Kelvin wake investigation based on the static Kelvin wake model failed to reflect time-varying characteristics, which are significant in the application of the Kelvin wake model. Therefore, a time-varying Kelvin wake model with consideration of geometric time-varying characteristics and the hydrodynamic equation is proposed in this paper, which reflects the wake’s time-varying change lacking in the conventional Kelvin wake investigation. The Doppler velocity measurement, measured by a specially designed radar, can be exploited to verify the time-varying model by the comparison of velocity fields. Ground-based multi-input multi-output (MIMO) millimeter wave radar imaging through the simultaneous switching of transceiver channels was used to obtain the Doppler velocity for the first time. Finally, promising results have been achieved, which are in good agreement with our proposed model in consideration of the experimental scene. The proposed time-varying model and radar equipment provide velocity measurements for the Kelvin wake observation, which contains huge application potential.