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We report the synthesis, characterization, and reactivities of two stable NiIII N-confused porphyrin (NCP) complexes. Metalation of 3-OEt NCP 1 with NiCl2 ⋅ 6H2 O in CHCl3 /EtOH gave 3-OEt NiII NCP 3 initially, which was easily oxidized in air to form the NiIII complex of NCP inner C-oxide 4. Bis-ethoxy-modified NiIII complex 5 was synthesized by oxidation of 3 with PIFA in ethanol and CHCl3 . The structures of 4 and 5 were determined by single-crystal X-ray diffraction analysis. An unusually long NiIII -C bond (2.170(9) A) was observed in 4. The g-factor (g>2.1) observed in the EPR spectra of 4 and 5 further confirmed that they are paramagnetic NiIII complexes. Comparative experiments showed that the 3-ethoxy group plays an important role in the formation of 4 and 5. Reduction of 4 and 5 with NaBH4 regenerated complex 3.

This paper presents a method to analyze the dynamic physical limits of a phase-shifted full bridge (PSFB) circuit used for the power supply of Magnetic Resonance Imaging (MRI) gradient amplifiers. Based on the time-optimal control theory, the detailed optimal transient response process under a sudden load current change is analyzed considering the sample time delay, the minimum voltage undershoot and the minimum recovery time are calculated. The analytic results are validated by simulations and experiments on a 120 V/30 A PSFB converter.

This paper presents a method for evaluations and measurements of a high frequency nanocrystalline core transformer for power converters. An experimental platform is set up to measure the B-H characteristics of the core and the performances of the transformer with a frequency range up to 100 kHz. Using the measured B-H characteristics, a 3D FEM model of the transformer is built to simulate the performances and calculate the equivalent circuit parameters of the transformer that will be verified by the experimental data. The results show that the B-H characteristics of the nanocrystalline core are non-linear with frequency but well linear before it starts to saturation at a magnetic field of 0.6∼0.8 T depending on the frequency. The linear relative permeabilities of the core are as high as around 20000 at room temperature, and the iron losses are so low that the efficiencies of the transformer are kept over 99% in the frequency range of under 100 kHz and with a magnetic field within 0.66 T.

This paper presents a capacitor voltage balancing method for the five-level active neutral-point clamped (5L-ANPC) converter using phase-shifted pulse-width modulation (PS-PWM), including the voltage balancing of DC-link capacitors and flying capacitors. With PS-PWM, the series connected switches are operated at fundamental frequency and the other switches are operated at a constant switching frequency. The relationship between the average neutral-point current and zero-sequence voltage is investigated and an optimum zero-sequence voltage can be calculated to regulate the neutral-point potential. The voltage across the flying capacitor is regulated by adjusting the switching duty cycles of two PWM signals, which varies the operation time of redundant switching states in each switching period. Simulation and experimental results are presented to verify the validity of this method.