Yunfeng Liu

Multiphase coupled inductors in pulse-width modulated (PWM) converters benefit from the reduced steady-state current ripple and fast transient performance. This article proposes a magnetic core geometry together with a butterfly interleaving winding arrangement to integrate the four-phase negative coupled inductors. It adopts the interleaving winding strategy usually used in planar transformers to reduce the proximity effect. Basically, each winding has two overlapped areas with other two windings. The two currents in the overlapped area are in opposite directions. The proximity effect is, therefore, reduced. Compared with the conventional nonoverlapped winding arrangement, finite element analysis simulation indicates more than 60% ac resistance reduction and almost 30% footprint minimization. Both design considerations and design guidelines for the multiphase buck converter with coupled inductors are presented. The magnetic core and winding structure are demonstrated in a 36–75 V (nominal at 48 V) to 30 V four-phase negative coupled buck converter as a front stage for datacenter applications. It is implemented on a six-layer printed circuit board (PCB) without any parallel winding connections, and can operate up to 1165 W. The experiment shows the prototype achieves 99.3% peak efficiency with 912 W/in ³ power density.

In view of the low efficiency of the current distribution transformer fault diagnosis methods, a transformer state identification method based on improved deep belief network(DBN) is proposed in this paper. Firstly, the operation state data of distribution transformer is classified, analyzed and standardized. On this basis, the bidirectional random butterfly optimization algorithm is used to dynamically optimize the parameters of the DBN, so as to provide the efficient calculation and processing state of the whole cycle of diagnosis and analysis, and realize the accurate and effective fault identification and diagnosis of transformer. The simulation results show that the accuracy of the proposed fault identification method is 98.76% and the analysis time is 7.456s, which has good network performance.

This paper investigates the gallium nitride (GaN) based bridgeless dual single-ended primary inductor converter (SEPIC) power factor correction (PFC) with full input voltage range zero-voltage-switching (ZVS) turn-on for the application of step down AC-DC converter. The operation principles for the bridgeless Dual-SEPIC PFC and the theoretical analysis for the ZVS operation has been investigated. Furthermore, a new magnetic integration has been proposed to assemble all three inductors, including one input inductor and two output side inductors into one E-I-E core. The integrated inductor reduces the total ferrite volume and makes the converter more compact. The inductance design for ZVS SEPIC PFC and the magnetic reluctance modeling for the E-I-E core with the coupled inductor has been analyzed. The effective equivalent inductance of the input inductor can be implemented with a much less number of turns by a carefully designed coupling coefficient. Finally, a 300W GaN-based MHz bridgeless Dual-SEPIC PFC with the integrated inductors is developed and tested with fullrange ZVS, 97% peak efficiency based on the ZVS extension strategy.

Micromachined resonant accelerometers (MRAs), especially those devices fabricated by silicon on glass technology, suffer from temperature drift error caused by inherent thermal stress. This paper proposes two structure designs to attenuate the effect of thermal stress. The first MRA structure is realized by optimizing the locations of the bonding anchors and utilizing a special-shaped substrate to isolate the thermal stress generated during the die attach process. The second structure is designed using an isolation frame fixed by a single anchor to replace all dispersed anchors associated with the suspension beams and micro-levers. Simulated and experimental results show that both of the MRA structures can effectively reduce the thermal stress effect. The experimental results on one MRA prototype indicate that the differential temperature sensitivity reduces down to 1.9 μg/°C and its 15-day bias stability reaches 1.4 μg.

Spin rate of a high-speed spinning-rotor gyroscope will make a significant impact on angular rate sensor performances such as the scale factor, resolution, measurement range, and bias stability. This paper presents the spin rate effects on performance indicators of a microelectromechanical systems (MEMS) gyroscope where a free-spinning rotor is electrostatically suspended in an evacuated vacuum cavity and functions as a dual-axis angular rate sensor. Theoretical models of the scale factor and measurement range of such a spinning-rotor gyroscope are derived. The experimental results indicate that the measured scale factors at different settings of the spin rate match well with the theoretical predication. In order to separate the disturbance component of the rotation control loop on the gyroscope output, a testing strategy is proposed by operating the gyroscope at different spin rates. Experimental results on a prototype gyroscope show that the squared drive voltage generated by the rotation control loop is approximately proportional to the noise of the gyroscope output. It was further investigated that an improved performance of such spinning-rotor gyroscopes can be achieved by operating the gyroscope rotor at an optimal spin rate.

This paper presents a novel digital closed loop microelectromechanical system (MEMS) accelerometer with the architecture and experimental evaluation. The complicated timing diagram or complex power supply in published articles are circumvented by using a charge pump system of adjustable output voltage fabricated in a 2P4M 0.35 µm complementary metal-oxide semiconductor (CMOS) process, therefore making it possible for interface circuits of MEMS accelerometers to be integrated on a single die on a large scale. The output bitstream of the sigma delta modulator is boosted by the charge pump system and then applied on the feedback comb fingers to form electrostatic forces so that the MEMS accelerometer can operate in a closed loop state. Test results agree with the theoretical formula nicely. The nonlinearity of the accelerometer within ±1 g is 0.222% and the long-term stability is about 774 µg.

The sensing mass of the MEMS sensor working in the closed-loop system can be driven not only by inertial force due to external acceleration, but also by elastic restoring force and the electrostatic driving force. As all the forces are included in the loop, the errors they bring in separately could be interrelated with each other. Driven by undistinguishable forces with initial biases due to the manufacturing procession of the sensor, the MEMS sensor consequently works with biases, which could be correlated with the errors of the accelerometer, such as nonlinearity. In order to make clear how nonlinearity comes into being, a model of MEMS sensor with initial biases is proposed, and the formula, which approximately shows the relationship between the nonlinearity of the accelerometer and the initial biases, is deduced. The model, which expatiates the tradeoff between nonlinearity and zero bias of the accelerometer, and helps to quantitatively determine how to adjust the proof bias as well as how much the mechanical manufacturing error can be accepted, could be useful while designing and debugging.