Hybrid Predictive Control with Simple Linear Control Based Circulating Current Suppression for Modular Multilevel Converters

The modular multilevel converter(MMC)has become a promising topology for widespread power converter applications.However,an evident circulating current flowing between the phases will increase system losses and complicate the heatsink design.This paper proposes a novel hybrid model predictive control method for MMCs.This method utilizes an indirect structure MPC and a sorting algorithm to implement current tracking and capacitor voltages balancing,considerably resulting in reduced calculation burden.In addition,different from the conventional MPC solutions,we add a simple proportional-integral(PI)controller to suppress circulating current through modifying the submodule(SM)inserted number,which is parallel to the MPC loop.This hybrid control solution combines both advantages of MPC and linear control,evidently resulting in improved performance of circulating current.Finally,the MATLAB/Simulink results of an 11-level MMC system verify the effectiveness of the proposed solution.

Precision measurement and suppression of low-frequency noise in a current source with double-resonance alignment magnetometers

Low-noise high-stability current sources have essential applications such as neutron electric dipole moment measurement and high-stability magnetometers. Previous studies mainly focused on frequency noise above 0.1 Hz while less on the low-frequency noise/drift. We use double resonance alignment magnetometers(DRAMs) to measure and suppress the low-frequency noise of a homemade current source(CS) board. The CS board noise level is suppressed by about 10 times in the range of 0.001-0.1 Hz and is reduced to 100 n A/√Hz at 0.001 Hz. The relative stability of CS board can reach2.2 × 10^(-8). In addition, the DRAM shows a better resolution and accuracy than a commercial 7.5-digit multimeter when measuring our homemade CS board. Further, by combining the DRAM with a double resonance orientation magnetometer,we may realize a low-noise CS in the 0.001-1000 Hz range.

Circulating Current Suppression for MMC-HVDC Systems with Asymmetric Arm Impedance

The modular multilevel converter(MMC)has been a highly promising topology in the high-voltage direct-current(HVDC)transmission area,where each arm of the MMC may consist of hundreds of series-connected submodules and an inductor.Due to its parameter inaccuracy,component aging,and so on,the component parameter in different arms of the MMC may be different,which may cause circulating current in the MMC-HVDC transmission system,and result in current deterioration,power losses,and electromagnetic interference,etc.In this paper,the circulating current suppressing(CCS)in the MMC-HVDC system,due to asymmetric arm impedance,is analyzed.Based on the mathematical analysis,a method of using an auxiliary circuit is proposed for the MMC to realize the CCS and improve the performance of the MMC-HVDC system.Simulation studies are conducted with PSCAD/EMTDC in the HVDC system,which confirms the feasibility of the proposed method.

Development of data acquisition and over-current protection systems for a suppressor-grid current with a neutral-beam ion source

Neutral beam injection is one of the effective auxiliary heating methods in magnetic-confinementfusion experiments. In order to acquire the suppressor-grid current signal and avoid the grid being damaged by overheating, a data acquisition and over-current protection system based on the PXI（PCI e Xtensions for Instrumentation） platform has been developed. The system consists of a current sensor, data acquisition module and over-current protection module. In the data acquisition module,the acquired data of one shot will be transferred in isolation and saved in a data-storage server in a txt file. It can also be recalled using NBWave for future analysis. The over-current protection module contains two modes： remote and local. This gives it the function of setting a threshold voltage remotely and locally, and the forbidden time of over-current protection also can be set by a host PC in remote mode. Experimental results demonstrate that the data acquisition and overcurrent protection system has the advantages of setting forbidden time and isolation transmission.

Double-ended passivator enables dark-current-suppressed colloidal quantum dot photodiodes for CMOS-integrated infrared imagers

Lead sulfide(PbS)colloidal quantum dot(CQD)photodiodes integrated with silicon-based readout integrated circuits(ROICs)offer a promising solution for the next-generation short-wave infrared(SWIR)imaging technology.Despite their potential,large-size CQD photodiodes pose a challenge due to high dark currents resulting from surface states on nonpassivated(100)facets and trap states generated by CQD fusion.In this work,we present a novel approach to address this issue by introducing double-ended ligands that supplementally passivate(100)facets of halidecapped large-size CQDs,leading to suppressed bandtail states and reduced defect concentration.Our results demonstrate that the dark current density is highly suppressed by about an order of magnitude to 9.6 nA cm^(2) at -10 mV,which is among the lowest reported for PbS CQD photodiodes.Furthermore,the performance of the photodiodes is exemplary,yielding an external quantum efficiency of 50.8%(which corresponds to a responsivity of 0.532 A W^(-1))and a specific detectivity of 2.5×10^(12) Jones at 1300 nm.By integrating CQD photodiodes with CMOS ROICs,the CQD imager provides high-resolution(640×512)SWIR imaging for infrared penetration and material discrimination.

Joint Limiting Control Strategy Based on Virtual Impedance Shaping for Suppressing DC Fault Current and Arm Current in MMC-HVDC Systems

This paper proposes a joint limiting control strategy for suppressing DC fault current and arm current in modular multilevel converter-based high-voltage direct current(MMC-HVDC) systems, which includes two target-oriented current limiting controls. To limit the DC fault current in the early fault stage, an equivalent modular multilevel converter(MMC) impedance is obtained, and its high-frequency part is reshaped by introducing virtual impedance, which is realized by adjusting the inserted submodules adaptively. Following the analysis of MMC control characteristics, the arm current limiting strategy is investigated, with results showing that the inner-loop control has significant effects on arm current and that a simple low-pass filter can reduce the arm current in the fault period. Finally, by combining the virtual impedance shaping and innerloop control, the fault currents of DC lines and MMC arms can be suppressed simultaneously, which can not only alleviate the interrupting pressure of the DC circuit breaker, but also prevent the MMC from being blocked by the arm overcurrent. Theoretical analysis conclusions and the proposed strategy are verified offline by a digital time-domain simulation on Power Systems Computer Aided Design/Electromagnetic Transients including DC platform, and experiment on a real-time digital simulator platform.

A Three-state Dual-inductance Bi-directional Converter and Its Control in Pulse-loaded Three-port Converters

The current-pulse load is generally characterized by wide frequency band and pulse variation,when it is directly connected to the power supply bus.The load power is presented as the instantaneous power.In order to balance the instantaneous power difference between the pulse load and the DC bus,a bi-directional DC/DC converter is usually connected in parallel to compensate for the current fluctuation caused by the characteristics of the pulse load.However,there is a large current spike in the bus current in the pre-stage when the pulse load is changed between light and heavy load.In this paper,a three-state dual-inductance bi-directional converter is proposed.In addition,the load current waveform is directly used to control the inductive branch switches,and an adaptive current feedback control strategy based on the valley voltage loop is proposed to control the power switches.The control method is applicable to the arbitrary change of the frequency and power of the pulse load.Finally,the experimental results show that the threestate dual-inductance bi-directional converter not only eliminates excessive bus current spikes,but also improves the transient response of the three-port power supply system.