DC Voltage Conditions Research Articles

Zero DC voltage ride through of a hybrid modular multilevel converter in HVDC systems

This study presents a comprehensive analysis and a suppression method of sub-modules’ (SMs’) voltage stress in the hybrid modular multilevel converters when riding through zero DC voltage faults in high-voltage direct-current (HVDC) systems. First, the general DC fault ride through (FRT) strategy considering the redundancy of the arm voltage generation scheme under a reduced dc-link voltage is derived. Then full-bridge sub-modules (FBSMs’) voltage stress for the conventional DC-FRT schemes with and without common-mode voltage injection are analysed. Finally, on the basis of the available full-bridge SM capacitor energy control strategy, an improved method implemented by energy interaction between half-bridge sub-modules and FBSMs is presented. The proposed DC-FRT scheme can make all SM capacitor voltages balanced at their rated values during the zero DC voltage conditions. Simulated results are provided to demonstrate the validity of the analytical results and the feasibility of the proposed DC-FRT scheme.

A Flexible PV-Powered Battery-Charging Scheme for Electric Vehicles

ABSTRACTThis paper presents a new design for a low-impact, fully controlled, and flexible self-adjusting DC side pulse-width modulation (PWM)-hybrid modulated filter compensation (HMFC) scheme for multi photovoltaic-arrays utilized for vehicle-to-grid battery-charging electric vehicle schemes. The flexible HMFC scheme developed by the first author as a member of dynamic hybrid capacitor compensation and filtering scheme is robust and effective as it ensures maximum energy utilization and low inrush current transients. In addition, it provides transient voltage damping for a stabilized common DC interface bus to the battery charger. The new flexible controller uses a regulated multi-loop error-driven, error-scaled, and de-coupled hybrid mode charging controller for the PWM switching scheme along with two MOSFET/IGBT (Metal Oxide Semiconductor Field Effect Transistor/Insulated Gate Bipolar Transistor) complementary switches based on ratings and are cascaded for proper voltage and current photovoltaic (PV) arrays utilized. The dynamic error-driven controller ensures reduction in inrush current and transient voltage conditions as well as compensation for cloudy and shadowy conditions by equalizing the maximum power utilization of the two PV arrays. This will ensure efficient PV solar-system energy utilization as well as fully de-coupled source-load operation for the new proposed multi modal Li-ion battery-charging controller. The multi-regulator error-driven proportional integrated derivative controllers with newly added acceleration and fast response auxiliary loops ensure efficient fast charging as well as common DC-bus stabilization under load excursions, temporary faults, and battery hybrid voltage-current-power (V-I-P) charging modes. The hybrid switched/modulated capacitive-filter compensator ensures limited current excursions for transient DC voltage conditions.

The DC Surface Flashover Performance Research of Polyimide Under Low-Energy Electron Irradiation Environment

When a spacecraft is irradiated by electron in space, the surface flashover phenomenon on dielectric materials of a spacecraft can happen under the condition of lower dc voltage. In order to know the characteristics of surface flashover voltage on dielectric materials, we had a research about the dc surface flashover voltage of dielectric materials. In this paper, we prepared pure polyimide (PI) sample, and had surface flashover experiment for pure PI under dc voltage by low-energy electron irradiation. The results show that when electron energy is <;20 keV, the surface flashover voltage of PI in vacuum can increase with the increase in the electron energy; when the electron energy is more than 20 keV, the dc surface flashover voltage can decrease slightly with the increase in the electron energy. When the density range of electron beam is changing from 0.175 to 1.75 μA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the dc surface flashover voltage of PI sample has an exponential decrease with the increase in the electron energy density, and this phenomenon is more obvious with the increase in the electron energy density. Also, we discussed the mechanism preliminarily of that electron beam energy and electron beam density influence on the dc surface flashover voltage.

Electrical tree growth characteristics in XLPE cable insulation under DC voltage conditions

The growth characteristics of electrical trees in XLPE cable insulation under DC voltage conditions were studied by a combination of treeing test and microscopic observation system. In the treeing test samples, the tip radius of the needle electrode was 5 μm, and the pin-plane distance was 2 mm. When a 70 kV DC voltage was applied on the samples for totally 10 hours, either continuously or intermittently, no trees appeared. So the trees for growth study were all initially triggered by a 50 kV standard lightning impulse. The DC voltages were applied periodically, so as to make it possible for the required observation and recording. Under the DC voltages, the electrical trees developed gradually from a single slender branch to a sparse bushlike structure, and tree channels were found to be non-conductive. The growth rates were rather slow compared with AC trees under the same condition. Grouping experiments showed that the tree length increased with the increasing number of cycles and amplitude of DC voltage, and it was also related to the voltage duration in each cycle at 60 kV. This tree growth pattern has been well explained by a nonconductive tree model and the equivalent circuit, and the discharges occurred in the tree channels are thought to be the driving force for tree growth. Under the condition of an unexpected grounding of the needle electrode, a new tree would initiate instantly from the needle tip, while an existed tree would grow very rapidly. This is correlated to the material damage caused by the sudden release of the injected charges. The work is useful for the recommendations on test arrangement and operation strategy of HVDC cables.

Solar PV and Battery Storage Integration using a New Configuration of a Three-Level NPC Inverter With Advanced Control Strategy

In this paper, a novel configuration of a three-level neutral-point-clamped (NPC) inverter that can integrate solar photovoltaic (PV) with battery storage in a grid-connected system is proposed. The strength of the proposed topology lies in a novel, extended unbalance three-level vector modulation technique that can generate the correct ac voltage under unbalanced dc voltage conditions. This paper presents the design philosophy of the proposed configuration and the theoretical framework of the proposed modulation technique. A new control algorithm for the proposed system is also presented in order to control the power delivery between the solar PV, battery, and grid, which simultaneously provides maximum power point tracking (MPPT) operation for the solar PV. The effectiveness of the proposed methodology is investigated by the simulation of several scenarios, including battery charging and discharging with different levels of solar irradiation. The proposed methodology and topology is further validated using an experimental setup in the laboratory.

Modified one‐cycle‐controlled three‐phase pulse‐width modulation rectifiers under low‐output DC voltage conditions

The saddle pulse-width modulation (PWM) that can be obtained by injecting third harmonic current into sampled three-phase input currents is proposed to introduce in the conventional one-cycle control (OCC) strategy-based three-phase PWMrectifier on this study. In addition, for the three-level boost-type neutral-point-clamped structure rectifiers such as three-phase Vienna rectifier, the fluctuation in the neutral-point-potential (NPP) is analysed under modified OCC strategy. The proposed control scheme can not only improve the utilisation of DC bus voltage and the efficiency of converter without sacrificing the advantages of the conventional OCC scheme, such as no phase-locked loop and constant switching frequency, but also is beneficial to suppress the ripple in the DC-link voltage. Moreover, the neutral-point voltage loop is added in the proposed OCC scheme, and the neutral-point voltage controller is employed for controlling the unbalance DC voltage in the NPP which caused by the non-uniformity of parameters of components. The validity of the theoretical analysis and feasibility of the modified OCC strategy are verified by system simulation and experimental results based on a 5-kW prototype.

제한된 환경에서의 해수냉각펌프용 유도전동기 최대출력 운전을 위한 약계자 제어

The induction motor is used for driving the special equipments such as warship and submarine pump due to robust structure and simple maintenance. Domestic and foreign warships use a wide range of voltages and the DC voltage sources mainly from battery. In the low voltage level, the <TEX>${\Delta}$</TEX>-connection operation of induction motor can be used for the maximum power. However, the temperature of the inverter increases because of the high input current. On the other hand, Y-connection operation of the induction motor does not cause a problem of temperature because of the low input current compared to the <TEX>${\Delta}$</TEX>-connection. But the lack of the supply voltage can not be avoided. Therefore, this paper suggests the algorithm of the optimum field weakening control to extend the operating range of the induction motor with maximum power in a limited thermal and DC voltage condition.

입력전류와 커패시터 전압의 맥동저감을 위한 개선된 LCCT Z-소스 DC-AC 인버터

In this study, an improved LCCT(Inductor-Capacitor-Capacitor-Trans) Z-source inverter(Improved LCCT ZSI) with characteristics of Quasi Z-source inverter(QZSI) and LCCT Z-source inverter(LCCT ZSI) is proposed. The proposed inverter can also reduce the voltage stress and input current/capacitor voltage ripples compared with conventional LCCT ZSI and Quasi ZSI. A two winding trans in Z-impedance network of the conventional LCCT ZSI is replaced by a three winding trans in the proposed inverter. To verify the validity of the proposed inverter, a DSP controlled hardware was made and PSIM simulation was executed for each method. Comparing the current and voltage ripples of each method under the condition of input DC voltage 70[V] and output AC voltage 76[Vrms], the input current and capacitor voltage ripple factors of the proposed inverter were low as 11[%] and 1.4[%] respectively. And, for generation of the same output AC voltage of each method, voltage stress of the proposed inverter was low as 175[V] under the condition of duty ratio D=0.15. As mentioned above, we could know that the proposed inverter have the characteristics of low voltage stress, low ripple factor and low operation duty ratio compared with the conventional methods. Finally, the efficiency according to load change/duty ratio and the transient state characteristics were discussed.

다이오드-커패시터 출력필터를 갖는 Quasi Z-소스 컨버터의 입력 전류와 출력전압 특성

This paper proposes a quasi Z-source converter(QZSC) with a diode-capacitor output filter to improve the output DC voltage boost ability. The proposed converter has the same quasi Z-source network topology compared with the conventional converter. But the proposed method is adopted a diode-capacitor filter as its output filter, since the conventional method is used an inductor-capacitor as its output filter. Under the condition of the same input-output DC voltage, the proposed method has more lower shoot-through duty ratio than the conventional method. Also, because the proposed converter has same voltage boost factor under lower shoot-through duty ratio compared with the conventional converter, the proposed converter can be operated with the lower capacitor voltage of Z-source network and the lower input current. To confirm the validity of the proposed method, PSIM simulation and a DSP based experiment were performed to acquire the output DC voltage 120[V] under the input DC voltage 80[V]. And the capacitor voltage and inductor current in Z-source network, the output voltage of each converter were compared and discussed.

듀티 비에 따른 단상 Z-소스 인버터의 효율과 출력 전압에 관한 연구

This paper was compared for the output voltage and efficiency of the single-phase Z-source inverter(ZSI) according to shoot through duty ratio D. The eight single-phase ZSI in this study are typical ZSI, Embedded ZSI(EZSI), Improved ZSI(IZSI), Quasi ZSI(QZSI), Series ZSI, Trans ZSI(TSI), Switched inductor ZSI(SL-ZSI) and Extended boost ZSI (exZSI). The eight ZSI are divided into two Groups. ; Group-1 which is ZSI with the ordinary voltage boost factor B, and Group-2 which is ZSI with the maximum voltage boost factor B. For the execution of the proposed study, the PSIM simulation was achieved under the condition of input DC voltage=150[V] of ZSI, load =30[Ω] and 60[㎐] output filter. The output voltage and efficiency of each ZSI were calculated within the limits of D=0.1∼0.4. As a result, the output peak voltage of Group-2 was suddenly increased in a specified duty ratio D, and its efficiency was rapidly decreased. On the contrary, Group-1 shown the output and efficiency characteristics without sudden change compared to Group-2 despite the duty ratio increase. The efficiency of the Group-2 was sharply declined at duty ratio D of the most output voltage, but, in case of Group-1, the efficiency was slightly declined. Finally, the input DC current of ZSI with DCM and CCM was discussed.

Preparation of ceramic coating on Ti substrate by Plasma electrolytic oxidation in different electrolytes and evaluation of its corrosion resistance

Ceramic oxide coatings (titania) were produced on Ti by micro-arc oxidation in different aluminate and carbonate based electrolytes. This process was conducted under constant pulsed DC voltage condition. The effect of KOH and NaF in aluminate based solution was also studied. The surface morphology, growth and phase composition of coatings were investigated using scanning electron microscope and X-ray diffraction. Corrosion behavior of the coatings was also examined by potentiodynamic polarization and electrochemical impedance spectroscopy. It was found that the sparking initiation voltage (spark voltage) had a significant effect on the form and properties of coatings. Coatings obtained from potassium aluminate based solution had a lower spark voltage, higher surface homogeneity and a better corrosion resistance than the carbonate based solution. Addition of NaF instead of KOH had improper effects on the homogeneity and adhesion of coatings which in turn caused a poor corrosion protection behavior of the oxide layer. AC impedance curves showed two time constants which is an indication of the coatings with an outer porous layer and an inner compact layer.

The Effect of AC Frequency on the Electrowetting Behavior of Ionic Liquids

This paper presents a study of electrowetting of ionic liquids (ILs) under AC voltages, where nine different ILs (including mono-, di-, and tricationic varieties) with three different AC frequencies (60 Hz, 1 kHz, 10 kHz) were experimentally investigated. The main foci of this study are (i) an investigation of AC frequency dependence on the electrowetting of ILs; (ii) obtaining theoretical relationships between the relevant factors that explain the experimentally achieved frequency dependence; and (iii) a systematic comparison of electrowetting of ILs using AC vs DC voltage fields. The frequency of the AC voltage was found to be directly related to the apparent contact angle change (Deltatheta) of the ILs. This relationship was further analyzed and explained theoretically. The electrowetting properties of ILs under AC voltages were compared to that under DC voltages. All tested ILs showed greater apparent contact angle changes with AC voltage conditions than with DC voltage conditions. The effect of structure and charge density also was examined. Electrowetting reversibility under AC voltage conditions was studied for few ILs. Finally, the physical properties and AC electrowetting properties of ILs were measured and tabulated.

Modeling of breakdown voltage of White Minilex Paper in the presence of voids under ac and dc conditions using fuzzy logic techniques

Occluded gaseous cavities within the insulating materials are potential sources of electrical trees which can lead to continuous deterioration and breakdown of materials. To determine the suitability of use and to acquire the data for the dimensioning of electrical insulation systems breakdown voltage of insulators should be determined. In this paper, fuzzy logic (FL) method is used to model breakdown voltages of White Minilex Paper samples based on experimental data generated in the laboratory. Different models are proposed with different shapes of the membership functions for the FL under both dc and ac voltage conditions. The cavities are created artificially with different dimensions. Low values of mean absolute errors of the estimated breakdown voltage of the test data show the effectiveness of such models.

Mechanical and electrical properties of diamond-like carbon films deposited by plasma source ion implantation

Diamond-like carbon (DLC) films were prepared by a plasma source ion implantation method with superposed negative pulse and negative DC voltage. Acetylene gas was used as working gas for plasma formation. A negative DC voltage and a negative pulse voltage were superposed and applied to the substrate holder. The DC voltage was changed in the range from 0 to −4.8kV and the pulse voltage was changed from −18 to −13.2kV. The films were annealed in the range of 200–450°C for 1h. The surface morphology of the films and the film thickness were observed by atomic force microscopy and scanning electron microscopy. The film structure was characterized by Raman spectroscopy. The hardness of DLC films was evaluated by an indentation method. Measurement of the electrical resistivity was performed using a four-point probe station. Furthermore, a ball-on-disc test with 2N load was employed to obtain information about the friction properties and sliding wear resistance of the films.The surface of the DLC films was very smooth and featureless. The deposition rate was changed with the DC voltage and pulse conditions. Integrated intensity ratios ID/IG of Raman spectroscopy and electrical resistivity of the DLC films changed with DC voltage. The electrical resistivity decreased with increasing ID/IG ratio. The ID/IG ratio was increased and the electrical resistivity was decreased with annealing temperature owing to graphitization. Very low friction coefficients around 0.05 were obtained for as-deposited films.

Static and dynamic effects due to electrostriction in GaN/AlN

A one-dimensional model accounting for electrostriction, lattice mismatch, piezoelectricity,and strain is presented with special emphasis on GaN/AlN heterostructures recentlyexamined extensively in the literature. It is shown that electrostriction, being asecond-order effect in the strain–electric field relation, plays a significant, sometimesdominant, contribution subject to DC voltage conditions and externally imposedhydrostatic pressure or AC conditions. It is argued that electrostriction, examined in athree-dimensional model, may give important contributions to the total strain atDC conditions even in the absence of hydrostatic pressure. Model results arebased on experimentally reported values for electrostriction coefficients in GaN.

Electrostriction in GaN/AlN heterostructures

A one-dimensional model accounting for electrostriction, lattice mismatch, piezoelectricity, and strain is presented with special emphasis on GaN/AlN heterostructures recently examined extensively in the literature. It is shown that electrostriction, being a second-order effect in the strain–electric field relation, plays a significant, sometimes dominant contribution subject to DC voltage conditions and externally imposed hydrostatic pressure. Model results are based on experimentally reported values for electrostriction coefficients in GaN.

Nonlinearities and piezoelectric fields in AlN∕GaN wurtzite heterostructures

A one-dimensional model for examining the combined influence of lattice mismatch, spontaneous polarization, piezoelectricity, strain, and nonlinear permittivity effects is described. Nonlinear permittivity effects in two-layer AlN∕GaN structures used in, e.g., heterojunction field effect transistors are shown to have a significant influence (approximately 20%) in the absence of interface charge screening due to strong electric fields in the thin-film AlN layer. Considerable reductions occur, however, in the electric field when interface charge screening is effectively reducing the importance of nonlinear permittivity effects. Determination of dynamic strain characteristics is performed for the case of a strong dc electric field in the AlN layer (due to short-circuit dc voltage conditions over the full structure) superimposed by a small ac voltage and it is shown that resonance frequencies exist being weakly affected by permittivity nonlinearities. As a corollary, it is found that a nonlinear permittivity analysis indicates that the material sound speed becomes electric field dependent due to piezoelectric coupling.

The 110-GHz Electron Cyclotron Range of Frequency System on JT-60U: Design and Operation

The electron cyclotron range of frequency (ECRF) system was designed and operated on the JT-60U to locally heat and control plasmas. The frequency of 110 GHz was adopted to inject the fundamental O-mode from the low field side with an oblique injection angle. The system is composed of four 1 MW-level gyrotrons, four transmission lines, and two antennae. The gyrotron is featured by a collector potential depression (CPD) and a gaussian beam output through a diamond window. The CPD enables JAERI to drive the gyrotron under the condition of the main DC voltage of 60 kV without a thyristor regulation. The gaussian mode from the gyrotron is effectively transformed to HE11 mode in the 31.75 mm diameter corrugated waveguide. About 75% of the output power of the gyrotrons can be injected into plasmas through the waveguides about 60 m in length. There are two antennae to control the deposition position of the EC wave during a plasma discharge. One is connected with three RF lines to steer the EC beams in the poloidal direction. The other is to control the EC beam in the toroidal and poloidal directions by two steerable mirrors.On the operation in 2000, the power of 1.5 to 1.6 MW for 3 s was successfully injected into plasmas using three gyrotrons. Local profile control was demonstrated by using the antennae. This capability was devoted to improve the plasma performance such as high Te production more than 15 keV and suppression of the MHD activities. In 2001, the fourth gyrotron, whose structure was improved for long pulse operation, has been installed for a total injection power of ~3 MW.

Tracking an individual streamer branch among others in a pulsed induced discharge

The electro-dynamical properties and the mutual influence of several simultaneously propagating streamers are investigated in a point-to-plane configuration in air at atmospheric pressure under impulse voltage. When a fast and short high voltage pulse is applied to the point, a bunch of streamer branches develops into the interval. Since no previous ionized path has been traced before in the gap, streamers spread in the whole gap, branching while propagating. This behaviour is quite different from streamers under DC voltage conditions, which successively extend on the point–plane axis. The aim of this work is an attempt to distinguish the properties of an individual streamer simultaneously propagating with the others, by means of fast techniques based on simultaneous streak and still photographs and space-time decoupled currents measurements. Especially, their mean velocity can be estimated. In most cases, an axial streamer is observed, propagating faster than the others. This result can be interpreted in terms of the electric field space distribution by means of a three-dimensional electrostatic solver. This analysis shows that a mutual electro-dynamical influence is exerted from one streamer on another.

A voltage-dependent and calcium-permeable ion channel in fused presynaptic terminals of Torpedo.

1. We used a preparation of fused presynaptic nerve terminals of Torpedo electromotor nerve and the patch-clamp technique for characterization of single ion channels. We report here of a large, nonselective ion channel which is highly voltage dependent. 2. The slope conductance of the I-V relation was estimated by either direct measurement of the single-channel current amplitude at different voltages (850 +/- 18 pS (SE); n = 9) or by variance analysis (834 +/- 23 pS; n = 5). 3. The voltage dependence was examined in three ways. At steady-state DC voltage conditions, NPo (the open probability times the number of channels in the patch) was estimated. At potentials < 0 mV, the probability of the channel to open is negligible and increases dramatically, within a very narrow voltage range, to > 50% at +8 mV (n = 8). 4. In pulse experiments, the activation time delay is shorter as the voltage step reaches more positive values. The mean time for half activation (T1/2) decreases from 15 ms at +10 mV to 4 ms at +30 mV (n = 5). 5. Ensemble currents exhibit rectification in response to voltage ramps at negative potentials (n = 10). 6. The channel was found to be nonselective. Its permeability to Na+, K+, Cl-, glutamate, Ba+2, and Ca+2, relative to Na+, was 1.00, 1.00, 1.22, 1.07, 0.85, and 0.62, respectively. 7. Based on the transport number of calcium, the calculated driving force, and the mean channel open time, we estimated the number of calcium ions entering the nerve terminal upon depolarization. This number is not substantially different from the number of ions entering through voltage-dependent, calcium-selective channels in other cells. 8. We speculate that this nonselective ion channel, may serve as a calcium entry route into the nerve terminal and hence be involved in transmitter release.