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• The time-variant transit time distribution model (SAS) is coupled with a physically based hydrological model (SWAT). • The coupled model (SWAT-SAS) considers the spatial heterogeneity of aquifer recharge and represents groundwater age release preferences at the subbasin level. • Although both the original and modified models simulated comparable in-stream nitrate concentrations, the nitrate legacy estimations within the aquifers differ. • More knowledge of nutrient legacy information is needed for watershed management and pollution control. The transit time distribution (TTD) is a lumped method to characterize the diverse flow paths of a hydrological system, and the StorAge Selection function (SAS) is one of the time-variant forms, representing the link between storage and outflow. Although it provides age information about the water parcels and nutrient legacy, the spatial heterogeneity cannot be captured by this method. While the distributed physically-based hydrological models (PBHMs) can reflect the spatial heterogeneous in climate, land cover and management, its simplification of subsurface processes prevents it from representing the subsurface nutrient transport and sometimes fails to capture nutrient legacy dynamics of the landscape. We attempted to couple SAS functions into a PBHM (SWAT) for calculating the nitrate dynamics of aquifers. The results show that both SWAT-SAS and SWAT can reproduce the in-stream dynamics of streamflow and nitrate concentration for the Upper Selke catchment; the coupled model allows more flexibility of storage release schemes and provides water age information of the aquifers; even though both the models simulated comparable in-stream nitrate concentrations, the nitrate store remained in aquifers varied, which will have varying implications for pollution goal assessment and nutrient management. [ABSTRACT FROM AUTHOR]

• SWAT has good applicability to the hydrological simulation of the karst area. • Severe storms primarily occur during April to July and November. • The risk of flooding is projected to increase under the five SSP-based future land use scenarios. • The severity of flood events is expected to escalate during the dry season, with runoff coefficients potentially increasing by up to 16%. With economic and social development, the inevitable conflict between growing populations and land use change has become increasingly prominent. In karst areas, such as the Lijiang River Basin (LRB) in South China, land use has undergone rapid and intense changes over the past few decades due to urbanization and agricultural development. Assessing the hydrological effects of future land use change scenarios in karst areas is essential for estimating potential flood risks. In this study, we constructed hydrological models for the LRB based on a widely used hydrological model (SWAT, Soil and Water Assessment Tool), analyzed the runoff coefficient (R c) at event scale, and evaluated the hydrological effects under future land use scenarios in 2100 based on five shared socio-economic pathways (SSPs). The results indicate that the simulated streamflow effectively replicated the hydrographs of the LRB. The model exhibited good performance, as evidenced by daily streamflow simulation with NSE greater than 0.65 and PBIAS within the range of ± 15 %. This demonstrates the applicability of SWAT in karst areas. The analysis of storm events revealed that severe storms in the LRB mainly took place between April and July and in November, with relatively long durations and high R c values. Under all five SSP-based future land use scenarios, it is predicted that flood risk will increase in the LRB. Notably, the severity of flood events during the dry season is expected to escalate, with R c potentially increasing by up to 16 %. To address environmental degradation and achieve sustainable development, it is imperative to adopt appropriate environment-friendly land use practices and implement effective land management strategies. [ABSTRACT FROM AUTHOR]

Three-phase transformerless multilevel converters are widely used in the high-voltage photovoltaic power generation systems because of their low total harmonic distortion, high power density, and high conversion efficiency. One three-level flying capacitor converter and dual T-type three-level circuits can be combined to derive the compact and cost-effective nested five-level converter. However, due to the lack of an isolation transformer, the common-mode current is generated to degrade the converter performance. First, the common-mode equivalent circuit model of the nested five-level converter is initially derived to further explore its common-mode current generation mechanism. Then, the zero common-mode space vector modulation (ZCM-SVM) is proposed to reduce the common-mode current, which chooses the specific zero common-mode voltage space vectors to synthesize the reference vector. Then, an advanced coordinate transformation is introduced to realize the flexible sector selection and reduce the complexity of the vector action time calculation. The proposed modulation achieves the common-mode current suppression with high dc bus voltage utilization. Finally, the effectiveness of the proposed ZCM-SVM strategy is verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

Multilevel converters are widely employed in the 30–50 kW medium-voltage grid-connected photovoltaic (PV) generation systems due to their higher power quality and lower switching losses compared with the two-level converters. Dual T-type three-level converters and one three-level diode neutral point clamped circuit can be integrated to derive a simplified five-level modular composited converter (5L-MCC) for the medium-voltage PV grid-connected systems. However, realizing the capacitor voltage balance is a challenge to enhance its reliability. First, the model of dc capacitor voltage variation of the 5L-MCC is discussed to expose a limitation once the nearest three-vector synthesis method is employed with conventional space vector modulation (SVM). In order to extend the operational range, a hybrid space vector modulation (HSVM) strategy is proposed, which integrates the optimized SVM switching sequence for the low-modulation ($M\,< \,0.5$ ) and a simplified vector synthesis method for the high-modulation region ( $M\geq 0.5$). The proposed hybrid modulation maintains the dc capacitor voltage balance over the full modulation range and power factor. Finally, the effectiveness of the proposed HSVM strategy is verified with the simulation and experimental results. [ABSTRACT FROM PUBLISHER]

This paper proposes the adoption of the inherent emitter stray inductance $L_{{\rm{eE}}}$ in high-power insulated gate bipolar transistor modules as a new dynamic thermo-sensitive electrical parameter (d-TSEP). Furthermore, a family of 14 derived dynamic TSEP candidates has been extracted and classified in voltage-based, time-based and charge-based TSEPs. Accordingly, the perspectives and the implementation challenges of the proposed method are discussed and summarized. Finally, high-power test platforms are designed and adopted to experimentally verify the theoretical analysis. [ABSTRACT FROM PUBLISHER]

Capacitor voltage ripple in the fundamental frequency is distinctive in the performance of modular multilevel converters (MMCs), unlike other voltage-source converters. First, in order to reveal the influence of capacitor voltage ripple, the coupling effect of conventional MMC double-loop control strategy is investigated to explain the unsatisfactory response. Then, decoupled current control with synchronous frequency damping is proposed, eliminating the coupling terms in the presented average value MMC model, which can improve the system dynamic behavior. Moreover, the damping index is defined and designed in the proposed control strategy to compromise between current decoupling and oscillation damping. Furthermore, the dynamic MMC characteristics with the decoupled current control and appropriate damping index are explored with detailed theoretical analysis. Finally, the simulation results validate the effectiveness of the proposed control strategy. [ABSTRACT FROM PUBLISHER]

Insulated-gate bipolar transistor (IGBT) short-circuit failure modes have been under research for many years, successfully paving the way for device short-circuit ruggedness improvement. The aim of this paper is to classify and discuss recent contributions about IGBT short-circuit failure modes, in order to establish the current state of the art and trends in this area. First, the concept of 3-D safe operating area is proposed as the IGBT's operational boundary to divide the device short-circuit failure modes into short-circuit $V_{{\rm{DC}}}/ V_{{\rm{rated}}}\hbox{--} I_{{\rm{SC}}}$ SOA limiting and short-circuit endurance time limiting groups. Then, the discussion is centered on currently reported IGBT short-circuit failure modes in terms of their relationships with the device 3-D short-circuit safe operating area (3D-SCSOA) characteristics. In addition, further investigation on the interaction of 3D-SCSOA characteristics is implemented to motivate advanced contributions in future dependence research of device short-circuit failure modes on temperature. Consequently, a comprehensive and thoughtful review of where the development of short-circuit failure mode research works of IGBT stands and is heading is provided. [ABSTRACT FROM AUTHOR]

This paper presents a high-power IGBT testing platform for uneven temperature conditions and its design criteria. Considering the influence of layout parasitic parameters on the measurement results, commutation rules and independent junction temperature control, a universal high-power switching characterization platform is built and operated. Importantly, it is capable of 3.6 kA current level test requirement, which can cover the largest current level for the state-of-the-art IGBT modules. To improve the test accuracy of double pulse test method, a compensation algorithm is proposed to eliminate the circuit power loss under high current test conditions. Moreover, in order to simulate the uneven junction temperature effects occurring in real life, the junction temperatures of inspected IGBT and freewheeling diode are controlled independently. Quantitative analyses of the switching characteristics for junction temperatures up to 125 °C are performed. [ABSTRACT FROM AUTHOR]

An energy-compressed dielectric barrier discharge (DBD) in the atmospheric-pressure air is established to improve the surface modification of the polymer films. The effective discharge time of per repetitive cycle in the DBD system is adjusted by employing an active regulated power source, which can compress the energy transferred to the DBD load in the time domain. The effect of the energy compression on the surface modification of the polyethylene films is studied at different energy densities and frequencies by using the contact angle measurement, the atomic force microscope, and the X-ray photoelectron spectroscope. The results show that, at the given energy density and frequency, the surface wettability is improved by increasing the energy compression degree due to the higher surface roughness and more oxygen-containing polar functional groups. Furthermore, less energy density is needed to achieve the same level of surface wettability by increasing the energy compression degree. The reasons for the high performance of the energy-compressed DBD are the increase of the reactive species density and the enhancement of the physical and chemical interactions. As a result, the energy-compressed DBD is a superior solution for the polymer surface modification. [ABSTRACT FROM AUTHOR]

An advanced hybrid LLC series resonant converter with integrated flying-capacitor cell is proposed in this paper to enable the high step-down conversion in the high input voltage applications. The inherent flying-capacitor branch in the primary side can effectively halve the primary switch voltage stress compared with the half-bridge LLC converters. And the input voltage can be shared equally and automatically between the two series half-bridge modules without additional balance circuit or control strategies due to the built-in flying-capacitor cell. Moreover, the inherent soft switching performance during wide load range that exists in the LLC converters is still kept to reduce the switching losses, which ensures the high efficiency. Besides, the proposed converter can be extended to further decrease the switch voltage stress by employing stacked connection. Finally, a 500 ∼ 640 V-input 48 V-output 1 kW prototype is built and tested to verify the effectiveness of the proposed converter. The results prove that the proposed converter is an excellent candidate for the high input voltage and high step-down dc/dc conversion systems. [ABSTRACT FROM PUBLISHER]

The dc symmetrical component method is introduced for the analysis and control of bipolar dc distribution systems under asymmetrical operation. This method is an extension of the classical symmetrical component theory in three-phase ac power systems. The asymmetrical voltage and current in the positive and negative poles are decomposed into symmetrical components in common and differential modes. The equivalent circuit for each mode is derived, which forms decoupled mode networks. Consequently, it allows for independent investigation of each mode, and provides an insightful view of the static and dynamic behavior of a bipolar dc power system. The dc symmetrical component method is a general approach which is applicable to different aspects of system design. As an example, an enhanced common-mode voltage regulation scheme is described. It suppresses common-mode LC resonance by adding active damping control, and reduces common-mode impedance to improve power quality and voltage stability. The major theoretical conclusions are verified by experimental results. [ABSTRACT FROM AUTHOR]

A new simple moving voltage average (SMVA) technique with fixed step direct control incremental conductance method is introduced to reduce solar photovoltaic voltage (VPV) oscillation under nonuniform solar irradiation conditions. To evaluate and validate the performance of the proposed SMVA method in comparison with the conventional fixed step direct control incremental conductance method under extreme conditions, different scenarios were simulated. Simulation results show that in most cases SMVA gives better results with more stability as compared to traditional fixed step direct control INC with faster tracking system along with reduction in sustained oscillations and possesses fast steady state response and robustness. The steady state oscillations are almost eliminated because of extremely small dP/dV around maximum power (MP), which verify that the proposed method is suitable for standalone PV system under extreme weather conditions not only in terms of bus voltage stability but also in overall system efficiency. [ABSTRACT FROM AUTHOR]

DC microgrids may have time-varying system structures and operation patterns due to the flexibility and uncertainty of distributed resources. This feature poses a challenge to conventional stability analysis methods, which are based on fixed and complete system models. To solve this problem, the concept of self-disciplined stabilization is introduced in this paper. A common stability discipline is established using the passivity-based control theory, which ensures that a microgrid is always stable as long as this discipline is complied by each individual converter. In this way, the stabilization task is localized to avoid investigating the entire microgrid, thereby providing immunity against system variations. Moreover, a passivity margin criterion is proposed to further enhance the stability margin of the self-disciplined control. The modified criterion imposes a tighter phase restriction to provide explicit phase margins and prevent under-damped transient oscillations. In line with this criterion, a practical control algorithm is also derived, which increases the converter's passivity through voltage feed forward. The major theoretical conclusions are verified by a laboratory DC microgrid test bench. [ABSTRACT FROM AUTHOR]

Single-phase voltage source transformerless inverters have been developed for many years and have been successful commercial applications in the distributed photovoltaic (PV) grid-connected systems. Moreover, many advanced industrial topologies and recent innovations have been published in the last few years. The objective of this paper is to classify and review these recent contributions to establish the present state of the art and trends of the transformerless inverters. This can provide a comprehensive and insightful overview of this technology. First, the generation mechanism of leakage current is investigated to divide the transformerless inverters into asymmetrical inductor-based and symmetrical inductor-based groups. Then, the concepts of dc-based and ac-based decoupling networks are proposed to not only cover the published symmetrical inductor-based topologies but also offer an innovative strategy to derive advanced inverters. Furthermore, the transformation principle between the dc-based and ac-based topologies is explored to make a clear picture on the general law and framework for the recent advances and future trend in this area. Finally, a family of clamped highly efficient and reliable inverter concept transformerless inverters is derived and tested to offer some excellent candidates for next-generation high-efficiency and cost-effective PV grid-tie inverters. [ABSTRACT FROM PUBLISHER]

In this paper, a decoupled controlled triport dc/dc converter is derived by combining two bidirectional single-phase buck–boost converters and one isolated full-bridge converter for multiple input source applications. The power density is improved, and the circuit structure is simplified because the power devices are completely shared in the primary side. Furthermore, the pulsewidth modulation plus phase-shift control strategy is introduced to provide two control freedoms and achieve the decoupled voltage regulation within a certain operating range. The duty cycle of the bidirectional buck–boost converters is adopted to balance the voltage between the two primary input terminals, while their phase angle is applied to regulate the accurate secondary voltage. Furthermore, zero-voltage-switching soft-switching operation is provided for all of the primary power switches due to the inherent phase-shift control scheme. Moreover, the two filter inductors in the bidirectional buck–boost converters and the isolated transformer in the full-bridge topology are integrated and replaced by the winding-cross-coupled inductors to reduce the component numbers and simplify the magnetic structure. Finally, a 1-kW prototype is built to verify all theoretical considerations, and it is shown that the proposed topology is particularly advantageous in the distributed power generation system with multiple energy sources. [ABSTRACT FROM PUBLISHER]

In this paper, a soft-switching dc/dc converter with secondary-side phase-shift control strategy is proposed to improve the conversion efficiency and minimize the primary switch voltage stress in the high input voltage applications. Zero-voltage-switching performance is achieved for both the primary- and secondary-side power devices in a wide load range to reduce the switching losses due to the secondary-side phase-shift control scheme. Furthermore, compared with the conventional phase-shift control mechanism, the circulating current at the freewheeling stage is effectively suppressed as well to minimize the conduction losses. Moreover, the voltage stress of the primary switches is only half of the input voltage by employing the improved three-level structure, which makes the low-voltage rated power devices available to improve the circuit performance. In addition, the converter can work in the buck, balance, and boost modes to achieve a relatively wide input voltage range, which is an expected advantage for the communication power system to minimize the electrolytic capacitors with an acceptable hold-up time. The operation principle is analyzed and experimental results of a 1-kW 100-kHz prototype are provided to verify the effectiveness and the advantages of the proposed converter. [ABSTRACT FROM AUTHOR]

In this paper, an isolated series asymmetrical half-bridge converter (SA-HBC) is proposed to satisfy the high power and high input-voltage requirements. In the proposed converter, two half-bridge modules with series configuration are adopted in the primary side to reduce the switch voltage stress to half of the input voltage. Moreover, the series half-bridge cells share the same transformer and leakage inductance, which simplifies the circuit structure. Zero-voltage-switching transition is achieved for all the active switches by employing the asymmetrical control scheme to reduce the switching losses. Furthermore, the voltages of the input capacitors are automatically balanced without any additional components or complex control methods. In addition, a family of dc–dc converters with series half-bridge structure is explored to give a universal discussion and extensive applications of the proposed contributions for the high input-voltage systems. Finally, a 500–600-V input 48-V output 1-kW prototype operating with 100 kHz switching frequency is built and tested to demonstrate the effectiveness of the proposed SA-HBC converter. The efficiency of 95% at full load is realized. [ABSTRACT FROM AUTHOR]

In order to eliminate the common-mode (CM) leakage current in the transformerless photovoltaic (PV) systems, the concept of the virtual dc bus is proposed in this paper. By connecting the grid neutral line directly to the negative pole of the dc bus, the stray capacitance between the PV panels and the ground is bypassed. As a result, the CM ground leakage current can be suppressed completely. Meanwhile, the virtual dc bus is created to provide the negative voltage level for the negative ac grid current generation. Consequently, the required dc bus voltage is still the same as that of the full-bridge inverter. Based on this concept, a novel transformerless inverter topology is derived, in which the virtual dc bus is realized with the switched capacitor technology. It consists of only five power switches, two capacitors, and a single filter inductor. Therefore, the power electronics cost can be curtailed. This advanced topology can be modulated with the unipolar sinusoidal pulse width modulation (SPWM) and the double frequency SPWM to reduce the output current ripple. As a result, a smaller filter inductor can be used to reduce the size and magnetic losses. The advantageous circuit performances of the proposed transformerless topology are analyzed in detail, with the results verified by a 500-W prototype. [ABSTRACT FROM AUTHOR]

First, the limitations of the conventional interleaved boost converters in high-step-up and high-output-voltage applications are addressed in this paper. Then, a general derivation law of the nonisolated converters from their isolated counterparts is proposed and studied to give a universal solution for high-performance topology deduction. By employing the direct energy transfer concept, a family of nonisolated high-step-up interleaved boost converters is originated to make the turns ratio of a built-in transformer as another design freedom for the voltage gain extension. The derived converters have the advantages of large voltage conversion ratio, low power switch voltage stress, small input current ripple, and zero-voltage-switching soft-switching performance. The steady-state operation of the derived converter is analyzed, and the circuit performance is summarized to explore its advantages in the high-step-up, high-output-voltage, and large-current conversion systems. Finally, a 1-kW prototype with 40-V input and 380-V output voltages is implemented and tested to show the effectiveness of the derived converters. One of the main contributions of this paper is that a clear picture is made on the universal derivation law to generate high-step-up and high-performance dc/dc converters. [ABSTRACT FROM PUBLISHER]

A high-efficiency fuel-cell power-generation system with an active-clamp flyback–forward converter is presented in this paper to boost a 12-V dc voltage into a 220-V 50-Hz ac voltage. The proposed system includes a high-efficiency high-step-up interleaved soft-switching flyback–forward converter and a full-bridge inverter. The front-end active-clamp flyback–forward converter has the advantages of zero-voltage-switching performance for all the primary switches, reverse-recovery-problem alleviation for the secondary output diodes, large voltage-conversion ratio, and small input-current ripple. Furthermore, there are two coupled inductors in the proposed converter. Each coupled inductor can work in the flyback mode when the corresponding main switch is in the turn-on state and in the forward mode when it is in the turnoff state, which takes full use of the magnetic core and improves the power density. In addition, the full-bridge inverter with an LC low-pass filter is adopted to provide low-total-harmonic-distortion ac voltage to the load. Therefore, high-efficiency and high-power-density conversion can be achieved in a wide input-voltage range by employing the proposed system. Finally, a 500-W prototype and another 1-kW converter are implemented and tested to verify the effectiveness of the proposed system. [ABSTRACT FROM AUTHOR]

The photovoltaic (PV) grid-connected power system in the residential applications is becoming a fast growing segment in the PV market due to the shortage of the fossil fuel energy and the great environmental pollution. A new research trend in the residential generation system is to employ the PV parallel-connected configuration rather than the series-connected configuration to satisfy the safety requirements and to make full use of the PV generated power. How to achieve high-step-up, low-cost, and high-efficiency dc/dc conversion is the major consideration due to the low PV output voltage with the parallel-connected structure. The limitations of the conventional boost converters in these applications are analyzed. Then, most of the topologies with high-step-up, low-cost, and high-efficiency performance are covered and classified into several categories. The advantages and disadvantages of these converters are discussed. Furthermore, a general conceptual circuit for high-step-up, low-cost, and high-efficiency dc/dc conversion is proposed to derive the next-generation topologies for the PV grid-connected power system. Finally, the major challenges of high-step-up, low-cost, and high-efficiency dc/dc converters are summarized. This paper would like to make a clear picture on the general law and framework for the next-generation nonisolated high-step-up dc/dc converters. [ABSTRACT FROM AUTHOR]

A novel isolated zero-voltage-transition (ZVT) boost converter with coupled inductors is proposed in this paper to satisfy the high power, high step-up, and isolated requirements. In the proposed converter, the input-parallel configuration is adopted to share the large input current and to reduce the conduction losses, while the output-series structure is employed to double the output voltage gain. Consequently, a transformer with a low turns ratio can be applied, which makes the transformer design and optimize easily. Moreover, the active clamp circuits are employed to reduce the switch voltage stress and to recycle the energy stored in the leakage inductance. The ZVT is achieved during the whole switching transition for all the active switches, so the switching losses can be reduced greatly. Furthermore, the diode reverse-recovery problem is partly solved due to the leakage inductance. In addition, the magnetic integration technology is applied to improve the efficiency and to reduce the magnetic component size. Finally, a 48-V input 380-V output 1-kW prototype operating with 100-kHz switching frequency is built and tested to demonstrate the effectiveness of the proposed converter. [ABSTRACT FROM PUBLISHER]

In this paper, a voltage multiplier cell is inserted in the conventional boost converter operated in continuous conduction mode (CCM) to provide another design freedom for the voltage-gain extension. Thus, the voltage conversion ratio is enlarged and the narrow turn-OFF period is avoided in the high step-up applications. Furthermore, the voltage multiplier cell makes the voltage stress of all the power devices lower than the high output voltage. As a result, the low-voltage-rated power devices can be employed to reduce the conduction losses and to improve the power device reliability. Moreover, zero-voltage switching soft-switching operation is achieved for the power MOSFETs in the whole-switching transition. Zero-current switching turn-OFF condition is provided for the diodes. Therefore, the power device switching losses and the diode reverse-recovery losses are minimized greatly. In addition, the input current ripple is reduced due to the CCM operation compared with most of the published single-stage single-phase high step-up converters, which makes it more advantageous in the hybrid electric vehicles and the fuel-cell power conversion systems. Finally, the experimental results from a 500-W, 36–380-V prototype are provided to validate the effectiveness of the proposed converter. [ABSTRACT FROM PUBLISHER]

A shunt active power filter (SAPF) is coupled with load admittance in weak grid conditions, which poses a challenge to stability analysis. In this article, the admittance model of the SAPF is developed, which reveals the coupling mechanism between SAPF and load concisely and accurately. On top of that, the stability region of the system is investigated. The passivity region of the load admittance to guarantee the system stability is first explored. However, the passivity region has a very narrowband at a specific frequency, which makes it difficult to achieve. The stability region is then studied and it turns out to be an extension of the passivity region, and especially the narrowband is expanded. Therefore, the stability region is much easier to meet. The stability-oriented design is then summarized in a flowchart. In the end, the effectiveness of the newly defined stability region is verified by experimental results. [ABSTRACT FROM AUTHOR]

In this paper, the impact of a double-sided press-pack insulated-gate-bipolar-transistor (PP IGBT) cooling structure on its thermal impedance distribution is studied and explored. A matrix thermal impedance network model is built by considering the multi-chip thermal coupling effect for the collector side of the PP IGBT. Moreover, a verification has been made by comparing the proposed matrix thermal network model and the conventional lumped RC network model provided by the manufacturer. It is concluded that the collector side has lower thermal resistance and dissipates about 88% of the heat generated by the IGBT chips inside the module. Then, a modular-multilevel-converter high-voltage-direct-current (MMC-HVDC)-based type test setup composed of the press-pack IGBT stacks is established and the junction temperature is calculated with the proposed thermal model and verified by temperature measurements. [ABSTRACT FROM AUTHOR]

[Display omitted] • HSPF-WASP integrated modeling system for Rappahannock River Basin is feasible. • Integrated model provides the nitrogen load of each sub-watershed and river segment. • NPS pollution output more correlated with watershed area than mutual reactions. • Nitrogen was more susceptible in winter and stable in summer. • Similar effects on ammonia by temperature of 1.5 ∼ 2℃ and streamflow of 20 ∼ 50% The high nitrogen load in most rivers across the globe causes various environmental issues. Non-point source (NPS) pollution within a watershed has a significant impact on water quality management and prediction accuracy in rivers. Temperature and streamflow, as the most important environmental indicators, significantly affect water pollution management. This study takes the Rappahannock River Basins (RRB) as a case and adopts the method of coupling land and river models to improve the simulation accuracy of river pollution, outputs and analyzes the temporal and spatial distributions of nitrogen pollution in RRB, assesses the impact of temperature and streamflow changes on nitrogen pollution in water bodies. The results show that NPS pollution is mainly affected by topography and land use, and the annual output is more correlated with the watershed area. Temperature is negatively correlated with NH 4 -N and NO 3 -N in the Rappahannock River. Nitrogen is more susceptible to streamflow in winter; but in summer, it was stable and even showed the opposite changing tendency to winter. Changes in temperature of 1.5 ∼ 2℃ and streamflow of 20 ∼ 50% have similar effects on NH 4 -N, while increasing streamflow can significantly increase the concentration of NO 3 -N, and most of these changes are very evident. NH 4 -N and NO 3 -N concentrations will increase in RRB when the summer temperature is below the long-term average. NH 4 -N concentration will increase when upstream streamflow (such as the amount of mountain snowmelt) decreases in winter, while NO 3 -N concentration will decrease. The establishment of the integrated model can provide the nitrogen pollution load of each sub-watershed and each segment, which can be used to develop the TMDL for the Rappahannock River. [ABSTRACT FROM AUTHOR]

Three-phase current reconstruction techniques with a single current sensor have been studied for permanent magnet synchronous machines (PMSMs) drive system due to its reducing cost and volume. In order to minimize the current reconstruction dead zone in the conventional method with a single dc-link current sensor, a strategy to couple multiple available positions through the single current sensor is proposed in this paper. With the proposed method, two independent equations of the stator currents can be obtained by sampling the single current sensor twice in both zero voltage vectors and active voltage vectors. By solving these two equations, the phase current reconstruction can be achieved accurately, which moves the current reconstruction dead zone toward six corner area of the space vector hexagon. Meanwhile, in order to guarantee the proposed method suitable in the whole linear modulation region, the suitable selection of the pulsewidth modulation switching period is analyzed in detail. Furthermore, the optimal selections of multiple sampling positions are discussed to lower the actual implementation difficulty of the proposed method. Finally, the experimental results on the PMSM demonstrate that the reconstructed phase currents with the proposed method can be always in consistent with the actual measured currents under different working conditions. [ABSTRACT FROM AUTHOR]

The thermal design of a highly reliable modular multilevel converter (MMC) is significant for the voltage-source-converter-based high-voltage direct current system, especially under the unbalanced ac grid fault. In this paper, the analytical thermal model of the MMC considering the fault ride-through strategy is established to explore the MMC dynamic thermal behavior under the single-phase-to-ground fault. With the established thermal model, the proportional relationship between the MMC dc current and submodule thermal imbalance factor is derived. By exploring the features of dc current, it is discovered that the asymmetrical ac voltage makes the dc current different among three phases, leading to the thermal imbalance among three phases. To solve this issue, the neutral-point-shift-based active thermal control method, which can reshape the MMC ac voltage and balance the three-phase dc current, is proposed. With the proposed control method, the thermal distribution among three phases becomes balanced and the junction temperature of the most stressed power device is significantly reduced. Furthermore, the performance analysis shows that the proposed method brings little effects on the circulating current suppression. Finally, the major theoretical conclusions are verified by a laboratory MMC test bench. [ABSTRACT FROM AUTHOR]

In this paper, a unified equivalent circuit model which can simplify the design and analysis of a family of high-voltage (HV) generation architectures based on the series–parallel (LCC) resonant converter is proposed. First, four HV generation architectures are reviewed in terms of the modularization level of HV transformers and rectifiers. Next, the steady-state, unified equivalent resistor and capacitor (RC) model that can be easily embedded into the resonant tank to replace the complex HV transformers and rectifiers is derived. The generic model can be applied to the HV generators with different architectures, different voltage multiplier topologies, stage, and polarities number. Further analysis of the power factor of the resonant tank, the voltage gain of HV generators, and electrical stresses of power components is achieved with the derived equivalent circuit model. The analysis reveals the inherent circuit properties among HV generators with different configurations. Subsequently, a comprehensive design methodology considering the power factor, conduction angle, and quality factor is presented, which leads to low electrical stresses on the components and high efficiency. Furthermore, the parameter selection constraint based on the power factor, conduction angle, and quality factor is derived, which can ensure the effective design outputs. Finally, the proposed unified equivalent model and comprehensive design methodology are validated by the experimental results of a 250 V input, 20 kV output 500 W HV generator hardware prototype with distributed transformers and voltage multipliers. [ABSTRACT FROM AUTHOR]

In this paper, a dynamic thermo-sensitive electrical parameter (DTSEP) for extracting the junction temperature of the trench gate/field-stop insulated gate bipolar transistor (IGBT) modules by using the maximum collector current falling rate is proposed. First, a theoretical model of the transient collector current during turn-off process is developed in terms of the behavior characteristics of the inside storage carriers. Then, the inherent linear relationship between the maximum collector current falling rate dIC/dt and junction temperature Tj is demonstrated and investigated. Fortunately, benefitting from the presence of the intrinsic parasitic inductance LeE between the Kelvin and power emitters of IGBT modules, the maximum dIC/dt can be easily measured to validate the theoretical analysis. Consequently, the maximum dIC/dt during turn-off process is a promising DTSEP for IGBT module junction temperature estimation. Moreover, the physical device parameters that affect the temperature sensitivity of the maximum dIC/dt are also discussed with the derived transient collector current falling model. [ABSTRACT FROM AUTHOR]

The modular multilevel converters (MMCs) are attractive topologies for the high-voltage direct current (HVDC) transmission system. Since the complicated structure of MMC with hundreds sub-modules per arm, building an accurate model to design the appropriate control strategy is one of the main technical challenges. In this paper, the average-value model (AVM) of the MMCs considering the sub-module capacitor voltage ripple is established to explore the control dynamic performance of MMCs. The effect of the sub-module capacitor voltage ripple on the MMC dynamic behavior is explored and the equivalent impedances of the DC and AC sides in the MMC converters are extracted and evaluated. Based on the equivalent impedances, a particular AVM of MMCs, which comprises the equivalent capacitors reflecting the capacitor voltage ripple, is presented. Furthermore, the detailed interaction of the AC side voltages, AC side currents and arm voltages and the coupling relationship of AC output current id and iq can be also precisely described by the introduced AVM. Finally, the effectiveness of the presented model is verified by the PSCAD/EMTDC simulations. [ABSTRACT FROM PUBLISHER]

This paper proposes a method to extract the junction temperature of high-voltage and high-power p-i-n diodes. It is investigated that the swept-out charge during reverse recovery current fall time is affected by junction temperature variation, which makes the swept-out charge a possible thermo-sensitive electrical parameter (TSEP). Thanks to the specific package of high-power IGBT modules with p-i-n diodes, the swept-out charge of a p-i-n diode can be measured by the induced voltage $v_{{eE}}$ on the parasitic inductor $L_{{eE}}$ between Kelvin and power emitter terminals. In typical inductive half-bridge circuit, the comprehensive analysis of commutation between the upper p-i-n diode and lower enabled IGBT discloses the monotonic relationship among the reverse recovery charge, reverse current fall time, and junction temperature. A double pulse chopper circuit is used to validate the theoretical analysis. The experimental results show that the dependence between diode junction temperature and charge during the reverse recovery current fall time is approximately linear. A three-dimensional lookup table is calibrated and can be used to estimate the p-i-n diode junction operating temperature. Finally, an experimental comparison of four TSEPs for p-i-n diode is presented to verify the feasibility of the implementation of proposed TSEP. [ABSTRACT FROM AUTHOR]

An advanced technique of energy compression with the third harmonic circulating current generation is presented in this paper to improve the surface treatment performance in the dielectric barrier discharge (DBD) systems. First, the relationship between the energy compression degree and contact angle is explored, which shows that the polymer surface wettability can be improved by the high energy compression degree in DBD. And then, an additional inductor is inserted into the resonant tank in the current-fed parallel-series resonant converter to generate the third harmonic current component, which can reduce the discharge-time-ratio and compress the energy transferred to the DBD loads. Furthermore, the method of rectifier-compensated fundamental plus third harmonic approximation (RCFTHA) is introduced to describe the current-fed parallel-series resonant converter by superposing two equivalent linear circuits operating at the fundamental and third harmonic frequencies, respectively. Consequently, the discharge-time-ratio optimization with the parallel-series resonant tank design is realized. Finally, the experimental results from a 350-W prototype substantiate the effectiveness of the energy compression with the third harmonic circulating current and the accuracy of RCFTHA. [ABSTRACT FROM AUTHOR]

Interior permanent magnet synchronous motor (IPMSM) with back electromotive-force (EMF) based sensorless field-oriented control (FOC) is widely used in medium-high speed applications. Unfortunately, the back EMF is too small to be estimated accurately during low speed operation. Hence, the current-frequency (I–f) control with controllable current vector is used for startup. However, the conventional I–f control is hard to realize the tradeoff between startup speed and load capacity, suffering high-acceleration and high-load startup failure. In this article, a current vector angle controller for sensorless IPMSM startup is proposed to adjust speed-up-stage current acceleration and constant-speed-stage current amplitude with load automatically. The proposed angle controller guarantees the current vector angle close to the maximum torque per ampere angle, which contributes to large startup torque, high operating efficiency and smooth transition from I–f startup to sensorless FOC. Furthermore, the robustness against parameters variation of angle controller is evaluated quantitatively. These theoretical advantages are verified in experiments with a 380 V, 1.5 kW IPMSM. In particular, the experimental results demonstrate that the proposed I–f control realizes full-load startup even with ${\rm{ \pm }}$ 50% flux linkage and ${\rm{ \pm }}$ 30% inductance variation. Furthermore, the startup acceleration auto-adjusts with load to reconcile startup speed and load capacity. [ABSTRACT FROM AUTHOR]

In this letter, an internal electric field shielding layer for high voltage winding of medium voltage high frequency transformer used in a modular cascaded medium voltage solid state transformer is proposed. Without breaking the litz wire insulation layer, the high electric field is effectively shielded by a semiconducting layer and an unclosed copper foil spiral, which are electrically connected together. Not only the electric field in the main wall insulation is uniformed but also the peak value of the internal field is greatly reduced, which will help to achieve lower partial discharge and higher insulation reliability. With this structure, the difficulties of pouring process and electric field estimation for the litz wire winding are both avoid. Finally, a no partial discharge 100 kW medium voltage high frequency transformer prototype with 75 kV base insulation level is built and verified with the insulation tests. [ABSTRACT FROM AUTHOR]

Following the continuous development of wide bandgap (WBG) devices and multilevel converter technology, medium voltage active front ends are becoming promising in future high-power-density and high-power applications. However, the cost issue is one of the major drawbacks, which stops the WBG devices from being widely applied in high-power areas. This article proposes a silicon carbide (SiC) and silicon (Si) hybrid five-level unidirectional rectifier. It requires only four SiC MOSFETs with relatively low blocking voltage and four Si diodes. Meanwhile, by adding snubber capacitors, all the Si devices are with low-speed switching, and the voltage stresses of fast SiC MOSFETs are minimized. In this article, operational analysis and carrier-based phase-disposition pulsewidth modulation scheme for this circuit are discussed in detail. The capacitor voltage balancing and unity power factor are both realized. Simulation and scaled-down experimental results are demonstrated to verify the proposed rectifier. Furthermore, the comparison of the hybrid five-level rectifiers is given to show the advantages of the proposed rectifier in terms of voltage stress, efficiency, and cost. [ABSTRACT FROM AUTHOR]

Switching ripple communication (SRC), which modulates the PWM carrier with digital data and takes the switching ripple as a signal carrier, helps power electronic converters to transfer digital data along with power. This article discusses the theory and implementation of SRC technology. It proves that the modulation using square wave and sinusoidal wave carriers is compatible. The fundamental principles of frequency hopping–differential phase shift keying (FH–DPSK) modulation are then analyzed in detail, and an improved FH–DPSK scheme is proposed to suppress output voltage disturbances, thereby maintaining power quality, reducing communication noise, and separating power control and data modulation. Furthermore, to evaluate the reliability of the communication technique, the effect of power conversion on communication is discussed in detail. Finally, a buck converter with a switching frequency of 100/83.3 kHz is set up, and the experiment achieves a 16.7 kbps bit rate using quaternary modulation, demonstrating the correctness of the scheme. [ABSTRACT FROM AUTHOR]

Multichip silicon carbide power modules with integrated snubbers are promising for large-capacity converters with high speed and cost efficiency. In the design stage, the parasitic inductance of module layout generally attracts the primary efforts of designers because of its severe impact on dynamic performance, e.g., voltage overshoot and transient current imbalance. However, due to the complexity of the heterogeneous layout, the solution space and development efficiency are always limited by the traditional manual design approach. Thus, this article proposes a generative method to optimize the layout autonomously. First, a graph model is built to describe heterogeneous layouts with all interconnectivity and design constraints retained. Based on the model, integer programming is introduced to generate layout templates with variable geometric topologies. Then, coupled with a self-developed discrete extractor, the Pareto-front is obtained by genetic algorithm, providing a tradeoff boundary for loop inductance and branch mismatch. The proposed method is systematic, flexible, and requires few designers’ expertise. A 1200 V/240 A half-bridge module is designed and fabricated to validate its capability. The experimental results show that the loop inductance of 5.59 nH is achieved, and less than 5% of the transient current imbalance is realized under 6.2 A/ns turn-on in the rated. [ABSTRACT FROM AUTHOR]

In the conventional full-bridge LLC converter, the duty cycle is kept as 0.5 and the phase-shift angle of the half-bridge modules is 0° to be a symmetrical operation, which makes the resonant tank operating frequency only equal to the switching frequency of the power devices. By regulating the duty cycles of the upper and lower switches in each half-bridge module to be 0.75 and 0.25 and the phase-shift angle of the half-bridge modules to be 180°, the asymmetrical duty cycle controlled full-bridge LLC resonant converter is derived. The proposed asymmetrical duty cycle controlled scheme halves the switching frequency of the primary switches. As a result, the driving losses are effectively reduced. Compared with the conventional full-bridge LLC converter, the soft-switching condition of the derived asymmetrical controlled LLC converter becomes easier to reduce the resonant current. Consequently, the conduction losses are decreased and the conversion efficiency is improved. The asymmetrical control scheme can be also extended to the stacked structure for high input voltage applications. Finally, two LLC converter prototypes both with 200-kHz resonant frequency for asymmetrical and symmetrical control schemes are built and compared to validate the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

The stitch wire configuration is widely adopted for large-area IGBT chips. However, an inhomogeneous wire current density introduces uneven self-heating and nonuniform chip heating, which exacerbates the chip thermal stress. In this article, a multicellular electro-thermal model considering the stitch-bonding wires is derived to optimize the wire layout parameters. Furthermore, the current density alleviation of wire bonds is investigated to be the most sensitive and effective method to comprehensively mitigate the thermal nonequilibrium and local overheating. Consequently, an improved multitier layout is proposed to further achieve thermal stress suppression without any additional components and advanced materials. Finally, a triple-tier-bonded IGBT module with optimal design parameters is fabricated to validate the thermal mitigation performance. The prototype experimental results demonstrate that the modeling error is less than 3.0%. The multitier layout decreases the current density by 57.6%, hence, the maximum and average chip temperature are reduced by 21.8% and 12.4%, respectively. [ABSTRACT FROM AUTHOR]

In this article, the output voltage control strategy of modular multilevel resonant dc converters (MMRDC) for medium-voltage wide-input-range applications is studied. First, the feasibility and influence of the switching frequency regulation and modulation index regulation are investigated in detail. It is found that the switching frequency choice has a significant effect on the voltage stress of arm inductors and the transformer. Then, based on these considerations, the modulation index regulation plus switching frequency regulation based design and control optimization is proposed. With the proposed design and control method, the switching frequency range for adapting to a wide input range is further reduced, especially under light load operating conditions. Besides, the high voltage stress on arm inductors is avoided and the high voltage dv/dt on the transformer is also eliminated. Finally, a laboratory prototype with 8–16 kV input and 375 V/60 kW output has been built and the experimental validation under a wide input range has been done. The efficiency over 96.4% under the wide input range proved the effectiveness of the optimized control methods. [ABSTRACT FROM AUTHOR]

This paper presents a digitally master–slave controlled parallel system of multiple LLC resonant converters with an inner resonant current control loop in each module. Theoretical analysis of the stability of individual modules and the system with an inner resonant current loop is proposed based on the envelop model, which reveals the principle of the performance improvement brought by the resonant current control loop. Moreover, the inner resonant current loop eliminates the differences in small-signal characteristics among different static operating points, thus facilitating the voltage loop design. The analysis of parallel operation and a complete control loop design guide for paralleled LLC resonant converters is presented based on a small-signal model rather than on software simulation. Finally, the stability analysis and design are elaborated and verified through a 16-kW experimental system of four modularized LLC resonant converters. [ABSTRACT FROM PUBLISHER]

The modularity of a modular multilevel dc converter (MMDC) makes it attractive for medium-voltage distribution systems. Inherent balance of submodule (SM) capacitor voltages is considered as an ideal property, which avoids a complex sorting process based on many measurements thereby reducing costs and enhancing reliability. This article extends the inherent balance concept previously shown for square-wave modulation to a multilevel version for MMDCs. A switching duty matrix dU is introduced: it is a circulant matrix of preset multilevel switching patterns with multiple stages and multiple durations. Inherent voltage balance is ensured with a full-rank dU. Circulant matrix theory shows that this is equivalent to a simplified common factor criterion. A nonfull rank dU causes clusters of SM voltage rather than a single common value, with the clusters indicated by the kernel of the matrix. A generalized coprime criterion is developed into several deductions that serve as practical guidance for design of multilevel circulant modulation. The theoretical development is verified through full-scale simulations and downscaled experiments. The effectiveness of the proposed circulant modulation in achieving SM voltage balance in an MMDC is demonstrated. [ABSTRACT FROM AUTHOR]

In this letter, a junction-temperature and current extraction method is presented based on the electroluminescence mechanism of the SiC mosfet body diode. Starting from the observation of two characteristic peaks in the emitted light spectrum, we proved that the junction temperature and the drain current can be simultaneously measured. This novel method consists of decoupling the relationship between the intensity of the electroluminescence peaks, the current, and the temperature. Through this optical method with inherent electrical isolation, the junction temperature and current in the SiC chip can be simultaneously measured with high precision. The total error of the junction temperature estimation is within ±3 °C, and the error of the current estimation is about ±0.2 A. [ABSTRACT FROM AUTHOR]

An advanced symmetrical voltage quadrupler rectifier (SVQR) is derived in this paper to serve as the secondary rectification topology, which helps to extend the converter voltage gain and reduce the output diode voltage stresses. The output voltage is four times of the conventional full-bridge voltage rectifier with the same transformer ratio, which benefits to reduce the turns ratio of the transformer and decrease the parasitic parameters. Also, low voltage-rated diodes with high switching performance can be applied to improve the efficiency. Meanwhile, all the diodes in SVQR have the same voltage and current stresses, which simplifies the thermal design. Furthermore, two output electrolytic capacitors are connected in series to share the high output voltage, and the voltage balance can be realized naturally without any additional voltage-sharing scheme. A clear picture is made in this paper to give a general framework and universal applications for the derived SVQRs for high step-up and high output voltage conversion systems. A dual boost converter is used as an example to demonstrate the clear advantages of the derived SVQRs. [ABSTRACT FROM AUTHOR]

Series connection of SiC power MOSFET is an attractive approach to expand the blocking voltage of SiC devices, whereas the dynamic voltage balancing among the series-connected devices is the most critical challenge of the technique. In this article, a simple, fast, and cost-effective dynamic voltage balancing circuit of the series-connected SiC MOSFETs is proposed to suppress the voltage imbalance among the devices. The proposed circuit is composed of a resistor-capacitor (RC) snubber with a coupled inductor to effectively sense the voltage imbalance and add a compensated signal to the gate driving voltage. In the article, the operation principle of the proposed method is described in detail and the parameter selection of the circuit is given. Then the optimized layout of the circuit in a typical half-bridge SiC power module is proposed to reduce the stray parameters introduced by the coupled inductor effectively. The proposed method is verified by experiments under different conditions. Compared with a purely RC snubber balancing strategy, the capacitor can be significantly reduced. Since only passive components are required in the feedback loop, the proposed method demonstrates a reliable and straightforward approach to achieve equal voltage sharing of the series-connected devices. [ABSTRACT FROM AUTHOR]

The oscillation frequency of the point of common coupling (PCC) voltage is proposed as a new detecting freedom for dc-based islanding events in this article. In the presented method, the voltage positive feedback with a frequency selection is applied to a distributed generator to make the PCC voltage oscillate at the selected frequency when islanding events occur. With the frequency information, islanding events can be identified by the small-amplitude oscillation superimposed on the normal dc voltage without the necessity of voltage amplitude to be shifted out of the normal range. Thus, the islanding events can be effectively distinguished from other abnormal conditions that lead to large voltage fluctuations, and so, the accuracy of islanding detection is improved. Also, the power quality at islanding events is enhanced, which provides important benefits for seamless transfer from the unintentional islanding conditions to the controlled islanding conditions. Moreover, the frequency selection is designed to only transfer the voltage signal at the sensitive frequency band of the islanding condition. As a result, the deterioration of stability caused by the voltage positive feedback can be relieved under the grid-connected condition compared to the existing methods. Finally, the effectiveness of the proposed method has been verified by both time-domain nonlinear simulation and experimental results. [ABSTRACT FROM AUTHOR]

DC transformers based on power electronics are key items of equipment for medium voltage dc (MVDC) distribution systems. Both high and low step-ratio dc–dc conversions are required to interface dc links at different voltages to form an integrated dc distribution system. The transformer-coupled resonant modular multilevel dc–dc converter (RMMC) is well-suited to high step-ratio connection between an MVDC network and a low voltage dc network but it is not suitable in low step-ratio conversion for linking two MVDC networks with similar but not identical voltages. This article presents a circuit evolution of the high step-ratio transformer-coupled RMMC into its low step-ratio transformer-less RMMC counterpart. These two RMMCs share the same structure and the same resonant process within the resonant submodule stack giving rise to the same operational advantages. Also, the circuit design experience can be readily transferred from one to the other. From these two base RMMC circuits, a family of RMMCs with further configurations is elaborated that provide a wider variety of connection options for MVDC distribution systems. In this circuit family, each high step-ratio transformer-coupled RMMC has a low step-ratio transformer-less RMMC counterpart and one can be transformed into the other via the circuit evolution process presented. The theoretical analysis for both high and low step-ratio RMMCs has been verified through full-scale simulations of medium voltage examples and further verified through down-scaled experiments on laboratory prototypes. [ABSTRACT FROM AUTHOR]

In this article, the arm phase-shift conducting modulation (PSCM) is proposed for the alternate arm multilevel converter (AAMC). With the PSCM strategy, the half-bridge (HB) structure could be applied as the submodule (SM) topology to reduce the circuit complexity of the full-bridge submodule based AAMC. First, the phase-shift angle is introduced to match the voltage modulation ratio and power factor of ac grid. The energy stored in the submodule capacitors are balanced by regulating the phase-shift angle. Then, the design criteria and operation performance for HBSM-AAMC with the proposed PSCM strategy are analyzed and presented. Compared with HBSM-modular multilevel converters (MMC), 18% HBSMs and 9% power devices are reduced with the proposed topology and modulation, resulting in the lower construction cost. Furthermore, the loss distribution is analyzed, and the operating losses of HBSM-AAMC are smaller than that of HBSM-MMC. Finally, the simulation and experiment are performed to verify the effectiveness of the derived topology and the proposed modulation strategy. [ABSTRACT FROM AUTHOR]

Integrated charging for electric vehicles (EVs) is considered as a good transitional scheme to expand the mileage range under the battery capacity limit. It can save the costs and reduce the volume by replacing the on-board charger, and can increase the charging power by reusing the high power propulsion system. Then, the charging and propulsion system will therefore be light and compact. As the charging topology is based on the propulsion system, the design degrees of freedom are not very high, further resulting in limited application. And the laws of topological construction are lacking. Therefore, most of the integrated charging schemes are designed for a specific occasion and are difficult to adopt for other applications. In this article, a general derivation law with a unified design criterion is proposed to improve the generality of integrated charging, by considering the charging torque and equivalent filter inductance of the multiplexed converter and motor. The criterion is illustrated and analyzed in a specific scheme that is applied in the Toyota plug-in hybrid EV. The simulation results in a software-in-the-loop environment and experimental results in a down-scaled prototype are demonstrated to confirm the validity of the unified criterion and the effectiveness of the control schemes. It is suitable for the design of integrated charging solutions with multiphase power and multiphase motors. [ABSTRACT FROM AUTHOR]