A novel current-source active power filter (APF) based on multi-modular converter with carrier phase-shifted SPWM (CPS-SPWM) technique is proposed. With this technique, the effect of equivalent high switching frequenc...A novel current-source active power filter (APF) based on multi-modular converter with carrier phase-shifted SPWM (CPS-SPWM) technique is proposed. With this technique, the effect of equivalent high switching frequency con-verter is obtained with low switching frequency converter. It is very promising in current-source APF that adopt super-conducting magnetic energy storage component.展开更多
The pulse-width-modulated(PWM)current-source converters(CSCs)fed electric machine systems can be considered as a type of high reliability energy conversion systems,since they work with the long-life DC-link inductor a...The pulse-width-modulated(PWM)current-source converters(CSCs)fed electric machine systems can be considered as a type of high reliability energy conversion systems,since they work with the long-life DC-link inductor and offer high fault-tolerant capability for short-circuit faults.Besides,they provide motor friendly waveforms and four-quadrant operation ability.Therefore,they are suitable for high-power applications of fans,pumps,compressors and wind power generation.The purpose of this paper is to comprehensively review recent developments of key technologies on modulation and control of high-power(HP)PWM-CSC fed electric machines systems,including reduction of low-order current harmonics,suppression of inductor–capacitor(LC)resonance,mitigation of common-mode voltage(CMV)and control of modular PWM-CSC fed systems.In particular,recent work on the overlapping effects during commutation,LC resonance suppression under fault-tolerant operation and collaboration of modular PMW-CSCs are described.Both theoretical analysis and some results in simulations and experiments are presented.Finally,a brief discussion regarding the future trend of the HP CSC fed electric machines systems is presented.展开更多
In medium voltage high power applications,multi-level current source converters(CSCs)are good candidate to increase system power region,reliability,and the quality of output waveforms.Compared with widely researched v...In medium voltage high power applications,multi-level current source converters(CSCs)are good candidate to increase system power region,reliability,and the quality of output waveforms.Compared with widely researched voltage source multi-level converters(MLCs),the current source MLCs have the advantages of inherent short-circuit protection,high power capability and high quality of output current waveforms.The main features of MLCs include reduced harmonics,lower switching frequency and reduced current stress on each device which is a particularly important for high power application with low voltage and high current requirements.This paper conducts a general review of the current research about MLCs in higher power medium voltage application.The different types of parallel structure based MLCs and the modulation methodologies will be introduced and compared.Specifically,the circuit analysis of the common-mode(CM)loop for parallel structures will be conducted,the common-mode voltage(CMV)and circulating current suppression methods developed on the base of multilevel modulations will be addressed.展开更多
Bifurcation and chaos in high-frequency peak current mode Buck converter working in continuous conduction mode（CCM） are studied in this paper. First of all, the two-dimensional discrete mapping model is established....Bifurcation and chaos in high-frequency peak current mode Buck converter working in continuous conduction mode（CCM） are studied in this paper. First of all, the two-dimensional discrete mapping model is established. Next, reference current at the period-doubling point and the border of inductor current are derived. Then, the bifurcation diagrams are drawn with the aid of MATLAB. Meanwhile, circuit simulations are executed with PSIM, and time domain waveforms as well as phase portraits in i_L–v_C plane are plotted with MATLAB on the basis of simulation data. After that, we construct the Jacobian matrix and analyze the stability of the system based on the roots of characteristic equations. Finally, the validity of theoretical analysis has been verified by circuit testing. The simulation and experimental results show that,with the increase of reference current I_（ref）, the corresponding switching frequency f is approaching to low-frequency stage continuously when the period-doubling bifurcation happens, leading to the converter tending to be unstable. With the increase of f, the corresponding Irefdecreases when the period-doubling bifurcation occurs, indicating the stable working range of the system becomes smaller.展开更多
In this paper, a new predictive control strategy for current source matrix converter (CSMC) is presented. Proposed predictive control strategy allows for creating output voltages with boost type voltage transfer ratio...In this paper, a new predictive control strategy for current source matrix converter (CSMC) is presented. Proposed predictive control strategy allows for creating output voltages with boost type voltage transfer ratio and desired frequency. The description of predictive control circuit of the CSMC is presented. Furthermore the simulation test results to confirm functionality of the proposed control strategy and converter properties under this strategy are shown.展开更多
The direct current-direct current （DC-DC） converter is designed for 1 T static random access memory （SRAM） used in display driver integrated circuits （ICs）, which consists of positive word-line voltage （VpwL）,...The direct current-direct current （DC-DC） converter is designed for 1 T static random access memory （SRAM） used in display driver integrated circuits （ICs）, which consists of positive word-line voltage （VpwL）, negative word-line voltage （VinyL） and half-VDD voltage （VHDo） generator. To generate a process voltage temperature （PVT）-insensitive VpWL and VNWL, a set of circuits were proposed to generate reference voltages using bandgap reference current generators for respective voltage level detectors. Also, a VOWL regulator and a VNWL charge pump were proposed for a small-area and low-power design. The proposed VpwL regulator can provide a large driving current with a small area since it regulates an input voltage （VCI） from 2.5 to 3.3 V. The VmvL charge pump can be implemented as a high-efficiency circuit with a small area and low power since it can transfer pumped charges to VNWL node entirely. The DC-DC converter for 1 T SRAM were designed with 0.11 μm mixed signal process and operated well with satisfactory measurement results.展开更多
AC currents are automatically calibrated by two different thermal current converter(TCC)designs.The two designs are different in the used number of the thermal-elements(TEs).Consequently they differ in their output el...AC currents are automatically calibrated by two different thermal current converter(TCC)designs.The two designs are different in the used number of the thermal-elements(TEs).Consequently they differ in their output electro motive force(EMF).Studying the effect of changing the output EMF is done in this paper through calibrating AC currents.5 mA and 5 A are accurately calibrated at different frequencies 55 Hz,1 kHz and10 kHz by the two TCCs.A comparison is made between the results to evaluate the effect of the output EMF value on the accuracy and the uncertainty of the low and higher AC current calibration.A LabVIEW program is designed for this accurate automatic calibration to overcome the problems of the manual calibration on the thermal converters.展开更多
Due to the decrease in the number of switches for the four-switch three-phase alternating current-direct current(FSTP AC-DC)converter,it can easily lead to DC-link capacitor voltage imbalance and the system stability ...Due to the decrease in the number of switches for the four-switch three-phase alternating current-direct current(FSTP AC-DC)converter,it can easily lead to DC-link capacitor voltage imbalance and the system stability reduction.In order to solve these problems,a finite control set model predictive control(FCS-MPC)for FSTP AC-DC converters with DC-link capacitor voltage balancing is proposed.In this strategy,in order to facilitate calculation,theαβcoordinate system model is established and all voltage vectors are evaluated by establishing a cost function.During the whole process,phase locked loop(PLL)and complex modulation strategy are not required.In the new established cost function,the additional objective term of suppressing capacitor voltage fluctuation is to eliminate effectively the capacitor voltages oscillations and deviations and improve the system reliability.The simulation results show that the proposed strategy can keep the capacitor voltage balancing and has good dynamic and static performance.展开更多
A novel 60 kW plasma converter with full range soft-switch by utilizing magnetizing inductance, leakage inductance and distributed inductance is introduced. The current injection phase-shifting technique is introduced...A novel 60 kW plasma converter with full range soft-switch by utilizing magnetizing inductance, leakage inductance and distributed inductance is introduced. The current injection phase-shifting technique is introduced into the research of soft-switching plasma converter successfully. The magnetic bias of transformer and the protection of switching parts are solved. The tests state that the power supply has excellent characteristics and higher efficiency and can meet the demand of large power plasma process well.展开更多
It was approved by the State Council in I984 to establish economicand technological development zones in 14 coastal port cities tofunction as windows for those cities to attract foreign investment,introduce advanced t...It was approved by the State Council in I984 to establish economicand technological development zones in 14 coastal port cities tofunction as windows for those cities to attract foreign investment,introduce advanced technology and management methods andexpand the export-oriented economy.Since 1992,18 other developmentzones have been approved by the Council,increasing the number ofsuch zones to 32.展开更多
GaN （gallium nitride） buck-rectifier has been proposed to realize high power density ISOP （input series and output parallel）-IPOS （input parallel and output series） converter-based dc distribution system. The ul...GaN （gallium nitride） buck-rectifier has been proposed to realize high power density ISOP （input series and output parallel）-IPOS （input parallel and output series） converter-based dc distribution system. The ultra-low loss bi-directional switch can be developed by the GaN power device because of the low on-resistance, the high-speed switching behavior and its own device structure. The buck-rectifier using the GaN bi-directional switches has the potential to achieve higher power density than the commonly utilized boost-rectifier. Availability of the GaN-HEMT （high electron mobility transistor） for the buck rectifier has been verified taking the theoretical limit of the on-resistance and the switching loss energy into account. Design consideration for a high power density buck-rectifier has been also conducted and the application effect of the GaN bidirectional switches has been evaluated quantitatively. The ISOP-IPOS converter-based dc （direct current） distribution system takes full advantage of the buck-rectifier and the rectifier using GaN devices contributes to realizing higher power density dc distribution system.展开更多
Pulse width modulated current-source converter(PWM-CSC)has great prospects in high voltage direct current transmission system(HVDC)due to its attractive features,such as flexible control characteristics,ability to avo...Pulse width modulated current-source converter(PWM-CSC)has great prospects in high voltage direct current transmission system(HVDC)due to its attractive features,such as flexible control characteristics,ability to avoid commutation failure,and lower cost.However,valve voltage of the PWM-CSC is the jump value between filter capacitors line-voltage and zero voltage due to its bypass operation,resulting in high peak voltage withstand by the converter for a rated HVDC system and high voltage ripper ratio.In order to solve these issues,an improved modulation method called specific carrier frequency of SPWM is proposed.After adopting the improved modulation method,the number of the reverse blocking integrated gate commutated thyristor(RB-IGCT)in series can reduce by 31.5%under unity power factor operation and the value of the dc choke can reduce by about 78.6%compared to traditional modulation methods,improving practicability of engineering application.Moreover,active power and reactive power operating range are derived under different modulation methods and the relationship of the power factor,modulation in q-axis and DC current are studied.Finally,effectiveness of the improved modulation method and comparisons of power operating range are verified in PSCAD/EMTDC.展开更多
Marine current energy conversion with turbines is a growing field of interest owing to its high energy density and predictability.For wind energy,three-bladed horizontal-axis turbines are the most common because of th...Marine current energy conversion with turbines is a growing field of interest owing to its high energy density and predictability.For wind energy,three-bladed horizontal-axis turbines are the most common because of their high power capture.Forces on blades are considerably higher in marine currents,presenting challenges to turbine design.Current research focuses on blade optimization and the selection of reliable transmission systems,and data from experiments conducted in natural environments are lacking.This paper focuses on a five-bladed vertical axis marine current turbine with a direct drive generator especially designed for low rotational speed and presents data from real-world experiments and 3D simulation models.The paper specifically investigates the influence of blade pitch angle on power capture.Experiments have been conducted at 1.42 m/s with a turbine in a river for blade pitch angles of 0°and+3°(the angle is defined as the leading edge of the blade rotating outward,perpendicular to,and opposite of the turbine axis).Two numerical 3D models,namely a vortex model and an actuator line model,have been used to simulate the turbine under the same conditions(1.42 m/s and 0°,+3°).The experimental and simulation results show that a 0°pitch angle gives a higher power capture power than a+3°pitch angle.In addition,simulation models were used to simulate the performance for an extended range at pitch angles of−3°to+3°,a fixed tip-speed ratio,and a step size of 1°.The simulations show that+1°gives the highest power coefficient and increases the average power capture by up to 0.6%.The performance of vertical axis marine current turbines can be improved by increasing the pitch angle to 1°in the positive direction.By contrast,a negative pitch angle can increase the average power capture of wind turbines.展开更多
Because of its controlled power factor and no commutation failure,current source converter(CSC)made up of reverse-blocking IGCTs(RB-IGCTs)offers broad application prospects in the field of HVDC system.Valve voltage an...Because of its controlled power factor and no commutation failure,current source converter(CSC)made up of reverse-blocking IGCTs(RB-IGCTs)offers broad application prospects in the field of HVDC system.Valve voltage and power operating range as the most important operating characteristics should be paid attention to but they are always contradictory.First,the relationship between valve voltage and modulation index is obtained.In particular,valve voltage of converter under the three typical modulation methods is compared,analyzed,and verified.Second,with the help of the independent control strategy and coordinated control strategy of both ends,power operating ranges of the three modulation methods are comprehensively analyzed and compared.Third,in order to solve power coupling at a low active power,the improved coordination control strategy at both ends in this paper is proposed and the relationships among active power,reactive power,DC current and phase angle difference are given in detail.Finally,a 500 kV/3 kA simulation system was built in PSCAD/EMTDC to obtain comparison results of the key operating characteristics of CSC under different modulation methods and the converter can realize unity power operation under random active power after adopting the improved coordinated control strategy,and DC current does not decrease to zero,verifying effectiveness of the coordinated control strategy.展开更多
An online partial discharge(PD) measurement performed on a high voltage direct current(HVDC) wall bushing successfully identified the presence of internal discharges.The wall bushing is a sulfur hexafluoride gas-insul...An online partial discharge(PD) measurement performed on a high voltage direct current(HVDC) wall bushing successfully identified the presence of internal discharges.The wall bushing is a sulfur hexafluoride gas-insulated bushing,rated for 500 kV dc and terminated on a thyristor-controlled HVDC converter bridge.The measurement of PD within the HVDC station environment is particularly challenging due to the high levels of electromagnetic noise caused by thyristor switching events and external air-corona from the neighboring high-voltage equipment.An additional challenge is the""mixed"voltage stress on the bushing insulation,which has both ac and dc high-voltage components.There are also fast transients during the firing of thyristors in the HVDC conversion process that cause added stress to the insulation.As a result,the analysis and interpretation of PD data for HVDC equipment is more complex;PD pulses may occur in response to the ac,dc,or switching transient voltage stresses.In this paper,an online PD measurement strategy for noise filtering and isolation of PD sources within the bushing are discussed.The PD measurement data is plotted on a phase-resolved diagram where the line supply power cord voltage was used as a reference. The phase-resolved diagram appears to suggest that the fast transients,caused during switching,trigger some PD events.Measurements were also performed with the aid of a modern PD measurement instrument having noise separation capabilities.The findings from the online PD measurements are verified with physical evidence,found after the bushing was removed from service,suggested internal PD had occurred inside the bushing.展开更多
Voltage source converter high-voltage direct current （VSC-HVDC） is a new power transmission technology pref- erable in small or medium power transmission. In this paper we discuss a new control system based on space...Voltage source converter high-voltage direct current （VSC-HVDC） is a new power transmission technology pref- erable in small or medium power transmission. In this paper we discuss a new control system based on space vector modulation （SVM） without any voltage line sensors. Using direct power control （DPC） SVM and a new double synchronous reference frame phase-locked loop （DSRF-PLL） approach, the control system is resistant to the majority of line voltage disturbances. Also, the system response has accelerated by using a feed forward power decoupled loop. The operation of this control strategy was verified in a SIMULINK/MATLAB simulation environment. To validate this control system, a 5 kV.A prototype system was constructed. Compared to the original controllers, the current total harmonic distortion （THD）, the active and reactive deviations and the DC voltage overshoot were lowered by 2.5%, 6.2% and 8%, respectively. The rectifier power factor in the worst condition was 0.93 and the DC voltage settling time was 0.2 s.展开更多
As a new generation of direct current(DC)transmission technology,voltage sourced converter(VSC)based high voltage direct current(HVDC)has been widely developed and applied all over the world.China has also carried out...As a new generation of direct current(DC)transmission technology,voltage sourced converter(VSC)based high voltage direct current(HVDC)has been widely developed and applied all over the world.China has also carried out a deep technical research and engineering application in this area,and at present,it has been stepped into a fast growing period.This paper gives a general review over China’s VSC based HVDC in terms of engineering technology,application and future development.It comprehensively analyzes the technical difficulties and future development orientation on the aspects of the main configurations of VSC based HVDC system,topological structures of converters,control and protection technologies,flexible DC cables,converter valve tests,etc.It introduces the applicable fields and current status of China’s VSC based HVDC projects,and analyzes the application trends of VSC based HVDC projects both in China and all over the world according to the development characteristics and demands of future power grids.展开更多
Wind energy sources have different structures and functions from conventional power plants in the power system.These resources can affect the exchange of active and reactive power of the network.Therefore,power system...Wind energy sources have different structures and functions from conventional power plants in the power system.These resources can affect the exchange of active and reactive power of the network.Therefore,power system stability will be affected by the performance of wind power plants,especially in the event of a fault.In this paper,the improvement of the dynamic stability in power system equipped by wind farm is examined through the supplementary controller design in the high voltage direct current(HVDC)based on voltage source converter(VSC)transmission system.In this regard,impacts of the VSC HVDC system and wind farm on the improvement of system stability are considered.Also,an algorithm based on controllability(observability)concept is proposed to select most appropriate and effective coupling between inputs-outputs(IO)signals of system in different work conditions.The selected coupling is used to apply damping controller signal.Finally,a fractional order PID controller(FO-PID)based on exchange market algorithm(EMA)is designed as damping controller.The analysis of the results shows that the wind farm does not directly contribute to the improvement of the dynamic stability of power system.However,it can increase the controllability of the oscillatory mode and improve the performance of the supplementary controller.展开更多
To reduce the probability of commutation failure(CF)of a line commutated converter based high-voltage direct current(LCC-HVDC)transmission,a DC chopper topology composed of power consumption sub-modules based on thyri...To reduce the probability of commutation failure(CF)of a line commutated converter based high-voltage direct current(LCC-HVDC)transmission,a DC chopper topology composed of power consumption sub-modules based on thyristor full-bridge module(TFB-PCSM)is proposed.Firstly,the mechanism of the proposed topology to mitigate CF is analyzed,and the working modes of TFB-PCSM in different operation states are introduced.Secondly,the coordinated control strategy between the proposed DC chopper and LCC-HVDC is designed,and the voltage-current stresses of the TFB-PCSMs are investigated.Finally,the ability to mitigate the CF issues and the fault recovery performance of LCC-HVDC system are studied in PSCAD/EMTDC.The results show that the probability of CF of LCC-HVDC is significantly reduced,and the performances of fault recovery are effectively improved by the proposed DC chopper.展开更多
This paper proposes a single-ended fault detection scheme for long transmission lines using support vector machine(SVM)for multi-terminal direct current systems based on modular multilevel converter(MMC-MTDC).The sche...This paper proposes a single-ended fault detection scheme for long transmission lines using support vector machine(SVM)for multi-terminal direct current systems based on modular multilevel converter(MMC-MTDC).The scheme overcomes existing detection difficulties in the protection of long transmission lines resulting from high grounding resistance and attenuation,and also avoids the sophisticated process of threshold value selection.The high-frequency components in the measured voltage extracted by a wavelet transform and the amplitude of the zero-mode set of the positive-sequence voltage are the inputs to a trained SVM.The output of the SVM determines the fault type.A model of a four-terminal DC power grid with overhead transmission lines is built in PSCAD/EMTDC.Simulation results of EMTDC confirm that the proposed scheme achieves 100%accuracy in detecting short-circuit faults with high resistance on long transmission lines.The proposed scheme eliminates mal-operation of DC circuit breakers when faced with power order changes or AC-side faults.Its robustness and time delay are also assessed and shown to have no perceptible effect on the speed and accuracy of the detection scheme,thus ensuring its reliability and stability.展开更多
文摘A novel current-source active power filter (APF) based on multi-modular converter with carrier phase-shifted SPWM (CPS-SPWM) technique is proposed. With this technique, the effect of equivalent high switching frequency con-verter is obtained with low switching frequency converter. It is very promising in current-source APF that adopt super-conducting magnetic energy storage component.
基金supported in part by the Jiangsu Natural Science Foundation of China under Grant BK20180013in part by the Shenzhen Science and Technology Innovation Committee(STIC)under Grant JCYJ20180306174439784.
文摘The pulse-width-modulated(PWM)current-source converters(CSCs)fed electric machine systems can be considered as a type of high reliability energy conversion systems,since they work with the long-life DC-link inductor and offer high fault-tolerant capability for short-circuit faults.Besides,they provide motor friendly waveforms and four-quadrant operation ability.Therefore,they are suitable for high-power applications of fans,pumps,compressors and wind power generation.The purpose of this paper is to comprehensively review recent developments of key technologies on modulation and control of high-power(HP)PWM-CSC fed electric machines systems,including reduction of low-order current harmonics,suppression of inductor–capacitor(LC)resonance,mitigation of common-mode voltage(CMV)and control of modular PWM-CSC fed systems.In particular,recent work on the overlapping effects during commutation,LC resonance suppression under fault-tolerant operation and collaboration of modular PMW-CSCs are described.Both theoretical analysis and some results in simulations and experiments are presented.Finally,a brief discussion regarding the future trend of the HP CSC fed electric machines systems is presented.
文摘In medium voltage high power applications,multi-level current source converters(CSCs)are good candidate to increase system power region,reliability,and the quality of output waveforms.Compared with widely researched voltage source multi-level converters(MLCs),the current source MLCs have the advantages of inherent short-circuit protection,high power capability and high quality of output current waveforms.The main features of MLCs include reduced harmonics,lower switching frequency and reduced current stress on each device which is a particularly important for high power application with low voltage and high current requirements.This paper conducts a general review of the current research about MLCs in higher power medium voltage application.The different types of parallel structure based MLCs and the modulation methodologies will be introduced and compared.Specifically,the circuit analysis of the common-mode(CM)loop for parallel structures will be conducted,the common-mode voltage(CMV)and circulating current suppression methods developed on the base of multilevel modulations will be addressed.
基金Project supported by the National Natural Science Foundation of China(Grant No.61376029)the Fundamental Research Funds for the Central Universities,Chinathe College Graduate Research and Innovation Program of Jiangsu Province,China(Grant No.SJLX15 0092)
文摘Bifurcation and chaos in high-frequency peak current mode Buck converter working in continuous conduction mode（CCM） are studied in this paper. First of all, the two-dimensional discrete mapping model is established. Next, reference current at the period-doubling point and the border of inductor current are derived. Then, the bifurcation diagrams are drawn with the aid of MATLAB. Meanwhile, circuit simulations are executed with PSIM, and time domain waveforms as well as phase portraits in i_L–v_C plane are plotted with MATLAB on the basis of simulation data. After that, we construct the Jacobian matrix and analyze the stability of the system based on the roots of characteristic equations. Finally, the validity of theoretical analysis has been verified by circuit testing. The simulation and experimental results show that,with the increase of reference current I_（ref）, the corresponding switching frequency f is approaching to low-frequency stage continuously when the period-doubling bifurcation happens, leading to the converter tending to be unstable. With the increase of f, the corresponding Irefdecreases when the period-doubling bifurcation occurs, indicating the stable working range of the system becomes smaller.
文摘In this paper, a new predictive control strategy for current source matrix converter (CSMC) is presented. Proposed predictive control strategy allows for creating output voltages with boost type voltage transfer ratio and desired frequency. The description of predictive control circuit of the CSMC is presented. Furthermore the simulation test results to confirm functionality of the proposed control strategy and converter properties under this strategy are shown.
基金supported by the Second Stage of Brain Korea 21 Projectsfinancially supported by Changwon National University in 2011-2013
文摘The direct current-direct current （DC-DC） converter is designed for 1 T static random access memory （SRAM） used in display driver integrated circuits （ICs）, which consists of positive word-line voltage （VpwL）, negative word-line voltage （VinyL） and half-VDD voltage （VHDo） generator. To generate a process voltage temperature （PVT）-insensitive VpWL and VNWL, a set of circuits were proposed to generate reference voltages using bandgap reference current generators for respective voltage level detectors. Also, a VOWL regulator and a VNWL charge pump were proposed for a small-area and low-power design. The proposed VpwL regulator can provide a large driving current with a small area since it regulates an input voltage （VCI） from 2.5 to 3.3 V. The VmvL charge pump can be implemented as a high-efficiency circuit with a small area and low power since it can transfer pumped charges to VNWL node entirely. The DC-DC converter for 1 T SRAM were designed with 0.11 μm mixed signal process and operated well with satisfactory measurement results.
文摘AC currents are automatically calibrated by two different thermal current converter(TCC)designs.The two designs are different in the used number of the thermal-elements(TEs).Consequently they differ in their output electro motive force(EMF).Studying the effect of changing the output EMF is done in this paper through calibrating AC currents.5 mA and 5 A are accurately calibrated at different frequencies 55 Hz,1 kHz and10 kHz by the two TCCs.A comparison is made between the results to evaluate the effect of the output EMF value on the accuracy and the uncertainty of the low and higher AC current calibration.A LabVIEW program is designed for this accurate automatic calibration to overcome the problems of the manual calibration on the thermal converters.
基金National Natural Science Foundation of China(No.61741508)
文摘Due to the decrease in the number of switches for the four-switch three-phase alternating current-direct current(FSTP AC-DC)converter,it can easily lead to DC-link capacitor voltage imbalance and the system stability reduction.In order to solve these problems,a finite control set model predictive control(FCS-MPC)for FSTP AC-DC converters with DC-link capacitor voltage balancing is proposed.In this strategy,in order to facilitate calculation,theαβcoordinate system model is established and all voltage vectors are evaluated by establishing a cost function.During the whole process,phase locked loop(PLL)and complex modulation strategy are not required.In the new established cost function,the additional objective term of suppressing capacitor voltage fluctuation is to eliminate effectively the capacitor voltages oscillations and deviations and improve the system reliability.The simulation results show that the proposed strategy can keep the capacitor voltage balancing and has good dynamic and static performance.
基金This project is supported by National Natural Science Foundation of China (No.59975030)Provincial Natural Science Foundation of Guangdong,China(No.04300691).
文摘A novel 60 kW plasma converter with full range soft-switch by utilizing magnetizing inductance, leakage inductance and distributed inductance is introduced. The current injection phase-shifting technique is introduced into the research of soft-switching plasma converter successfully. The magnetic bias of transformer and the protection of switching parts are solved. The tests state that the power supply has excellent characteristics and higher efficiency and can meet the demand of large power plasma process well.
文摘It was approved by the State Council in I984 to establish economicand technological development zones in 14 coastal port cities tofunction as windows for those cities to attract foreign investment,introduce advanced technology and management methods andexpand the export-oriented economy.Since 1992,18 other developmentzones have been approved by the Council,increasing the number ofsuch zones to 32.
文摘GaN （gallium nitride） buck-rectifier has been proposed to realize high power density ISOP （input series and output parallel）-IPOS （input parallel and output series） converter-based dc distribution system. The ultra-low loss bi-directional switch can be developed by the GaN power device because of the low on-resistance, the high-speed switching behavior and its own device structure. The buck-rectifier using the GaN bi-directional switches has the potential to achieve higher power density than the commonly utilized boost-rectifier. Availability of the GaN-HEMT （high electron mobility transistor） for the buck rectifier has been verified taking the theoretical limit of the on-resistance and the switching loss energy into account. Design consideration for a high power density buck-rectifier has been also conducted and the application effect of the GaN bidirectional switches has been evaluated quantitatively. The ISOP-IPOS converter-based dc （direct current） distribution system takes full advantage of the buck-rectifier and the rectifier using GaN devices contributes to realizing higher power density dc distribution system.
基金supported in part by Science and Technology Project of State Grid Corporation of China(5500202058059A0000).
文摘Pulse width modulated current-source converter(PWM-CSC)has great prospects in high voltage direct current transmission system(HVDC)due to its attractive features,such as flexible control characteristics,ability to avoid commutation failure,and lower cost.However,valve voltage of the PWM-CSC is the jump value between filter capacitors line-voltage and zero voltage due to its bypass operation,resulting in high peak voltage withstand by the converter for a rated HVDC system and high voltage ripper ratio.In order to solve these issues,an improved modulation method called specific carrier frequency of SPWM is proposed.After adopting the improved modulation method,the number of the reverse blocking integrated gate commutated thyristor(RB-IGCT)in series can reduce by 31.5%under unity power factor operation and the value of the dc choke can reduce by about 78.6%compared to traditional modulation methods,improving practicability of engineering application.Moreover,active power and reactive power operating range are derived under different modulation methods and the relationship of the power factor,modulation in q-axis and DC current are studied.Finally,effectiveness of the improved modulation method and comparisons of power operating range are verified in PSCAD/EMTDC.
基金Supported by Jgust Richert,Standup for Energy and Vattenfall,the Swedish National Infrastructure for Computing(SNIC)at NSC at Linköping University partially funded by the Swedish Research Council under Grant Nos.2021/23-539 and 2021/5-443.
文摘Marine current energy conversion with turbines is a growing field of interest owing to its high energy density and predictability.For wind energy,three-bladed horizontal-axis turbines are the most common because of their high power capture.Forces on blades are considerably higher in marine currents,presenting challenges to turbine design.Current research focuses on blade optimization and the selection of reliable transmission systems,and data from experiments conducted in natural environments are lacking.This paper focuses on a five-bladed vertical axis marine current turbine with a direct drive generator especially designed for low rotational speed and presents data from real-world experiments and 3D simulation models.The paper specifically investigates the influence of blade pitch angle on power capture.Experiments have been conducted at 1.42 m/s with a turbine in a river for blade pitch angles of 0°and+3°(the angle is defined as the leading edge of the blade rotating outward,perpendicular to,and opposite of the turbine axis).Two numerical 3D models,namely a vortex model and an actuator line model,have been used to simulate the turbine under the same conditions(1.42 m/s and 0°,+3°).The experimental and simulation results show that a 0°pitch angle gives a higher power capture power than a+3°pitch angle.In addition,simulation models were used to simulate the performance for an extended range at pitch angles of−3°to+3°,a fixed tip-speed ratio,and a step size of 1°.The simulations show that+1°gives the highest power coefficient and increases the average power capture by up to 0.6%.The performance of vertical axis marine current turbines can be improved by increasing the pitch angle to 1°in the positive direction.By contrast,a negative pitch angle can increase the average power capture of wind turbines.
基金supported in part by Science and Technology Project of State Grid Corporation of China.(5500202058059A0000).
文摘Because of its controlled power factor and no commutation failure,current source converter(CSC)made up of reverse-blocking IGCTs(RB-IGCTs)offers broad application prospects in the field of HVDC system.Valve voltage and power operating range as the most important operating characteristics should be paid attention to but they are always contradictory.First,the relationship between valve voltage and modulation index is obtained.In particular,valve voltage of converter under the three typical modulation methods is compared,analyzed,and verified.Second,with the help of the independent control strategy and coordinated control strategy of both ends,power operating ranges of the three modulation methods are comprehensively analyzed and compared.Third,in order to solve power coupling at a low active power,the improved coordination control strategy at both ends in this paper is proposed and the relationships among active power,reactive power,DC current and phase angle difference are given in detail.Finally,a 500 kV/3 kA simulation system was built in PSCAD/EMTDC to obtain comparison results of the key operating characteristics of CSC under different modulation methods and the converter can realize unity power operation under random active power after adopting the improved coordinated control strategy,and DC current does not decrease to zero,verifying effectiveness of the coordinated control strategy.
基金Manitoba Hydro for funding and supporting this research
文摘An online partial discharge(PD) measurement performed on a high voltage direct current(HVDC) wall bushing successfully identified the presence of internal discharges.The wall bushing is a sulfur hexafluoride gas-insulated bushing,rated for 500 kV dc and terminated on a thyristor-controlled HVDC converter bridge.The measurement of PD within the HVDC station environment is particularly challenging due to the high levels of electromagnetic noise caused by thyristor switching events and external air-corona from the neighboring high-voltage equipment.An additional challenge is the""mixed"voltage stress on the bushing insulation,which has both ac and dc high-voltage components.There are also fast transients during the firing of thyristors in the HVDC conversion process that cause added stress to the insulation.As a result,the analysis and interpretation of PD data for HVDC equipment is more complex;PD pulses may occur in response to the ac,dc,or switching transient voltage stresses.In this paper,an online PD measurement strategy for noise filtering and isolation of PD sources within the bushing are discussed.The PD measurement data is plotted on a phase-resolved diagram where the line supply power cord voltage was used as a reference. The phase-resolved diagram appears to suggest that the fast transients,caused during switching,trigger some PD events.Measurements were also performed with the aid of a modern PD measurement instrument having noise separation capabilities.The findings from the online PD measurements are verified with physical evidence,found after the bushing was removed from service,suggested internal PD had occurred inside the bushing.
文摘Voltage source converter high-voltage direct current （VSC-HVDC） is a new power transmission technology pref- erable in small or medium power transmission. In this paper we discuss a new control system based on space vector modulation （SVM） without any voltage line sensors. Using direct power control （DPC） SVM and a new double synchronous reference frame phase-locked loop （DSRF-PLL） approach, the control system is resistant to the majority of line voltage disturbances. Also, the system response has accelerated by using a feed forward power decoupled loop. The operation of this control strategy was verified in a SIMULINK/MATLAB simulation environment. To validate this control system, a 5 kV.A prototype system was constructed. Compared to the original controllers, the current total harmonic distortion （THD）, the active and reactive deviations and the DC voltage overshoot were lowered by 2.5%, 6.2% and 8%, respectively. The rectifier power factor in the worst condition was 0.93 and the DC voltage settling time was 0.2 s.
基金This work was supported by National Natural Science Foundation of China(No.51261130471).
文摘As a new generation of direct current(DC)transmission technology,voltage sourced converter(VSC)based high voltage direct current(HVDC)has been widely developed and applied all over the world.China has also carried out a deep technical research and engineering application in this area,and at present,it has been stepped into a fast growing period.This paper gives a general review over China’s VSC based HVDC in terms of engineering technology,application and future development.It comprehensively analyzes the technical difficulties and future development orientation on the aspects of the main configurations of VSC based HVDC system,topological structures of converters,control and protection technologies,flexible DC cables,converter valve tests,etc.It introduces the applicable fields and current status of China’s VSC based HVDC projects,and analyzes the application trends of VSC based HVDC projects both in China and all over the world according to the development characteristics and demands of future power grids.
文摘Wind energy sources have different structures and functions from conventional power plants in the power system.These resources can affect the exchange of active and reactive power of the network.Therefore,power system stability will be affected by the performance of wind power plants,especially in the event of a fault.In this paper,the improvement of the dynamic stability in power system equipped by wind farm is examined through the supplementary controller design in the high voltage direct current(HVDC)based on voltage source converter(VSC)transmission system.In this regard,impacts of the VSC HVDC system and wind farm on the improvement of system stability are considered.Also,an algorithm based on controllability(observability)concept is proposed to select most appropriate and effective coupling between inputs-outputs(IO)signals of system in different work conditions.The selected coupling is used to apply damping controller signal.Finally,a fractional order PID controller(FO-PID)based on exchange market algorithm(EMA)is designed as damping controller.The analysis of the results shows that the wind farm does not directly contribute to the improvement of the dynamic stability of power system.However,it can increase the controllability of the oscillatory mode and improve the performance of the supplementary controller.
基金supported by National Natural Science Foundation of China(No.51877077)。
文摘To reduce the probability of commutation failure(CF)of a line commutated converter based high-voltage direct current(LCC-HVDC)transmission,a DC chopper topology composed of power consumption sub-modules based on thyristor full-bridge module(TFB-PCSM)is proposed.Firstly,the mechanism of the proposed topology to mitigate CF is analyzed,and the working modes of TFB-PCSM in different operation states are introduced.Secondly,the coordinated control strategy between the proposed DC chopper and LCC-HVDC is designed,and the voltage-current stresses of the TFB-PCSMs are investigated.Finally,the ability to mitigate the CF issues and the fault recovery performance of LCC-HVDC system are studied in PSCAD/EMTDC.The results show that the probability of CF of LCC-HVDC is significantly reduced,and the performances of fault recovery are effectively improved by the proposed DC chopper.
文摘This paper proposes a single-ended fault detection scheme for long transmission lines using support vector machine(SVM)for multi-terminal direct current systems based on modular multilevel converter(MMC-MTDC).The scheme overcomes existing detection difficulties in the protection of long transmission lines resulting from high grounding resistance and attenuation,and also avoids the sophisticated process of threshold value selection.The high-frequency components in the measured voltage extracted by a wavelet transform and the amplitude of the zero-mode set of the positive-sequence voltage are the inputs to a trained SVM.The output of the SVM determines the fault type.A model of a four-terminal DC power grid with overhead transmission lines is built in PSCAD/EMTDC.Simulation results of EMTDC confirm that the proposed scheme achieves 100%accuracy in detecting short-circuit faults with high resistance on long transmission lines.The proposed scheme eliminates mal-operation of DC circuit breakers when faced with power order changes or AC-side faults.Its robustness and time delay are also assessed and shown to have no perceptible effect on the speed and accuracy of the detection scheme,thus ensuring its reliability and stability.
