Juan Carlos Balda

Power Conversion With SiC Devices at Extremely High Ambient Temperatures

This paper evaluates the capability of SiC devices for operation under extremely high ambient temperatures. To this end, the authors packaged SiC JFET and Schottky barrier diodes (SBD) in thermally stable packages and built a high-temperature inductor to be evaluated in a DC-DC buck converter. The DC characteristics of the SiC JFET devices were first measured at ambient temperatures ranging from room temperature up to 450 degC. The experimental results show that the device can operate at 450 degC, which is impossible for conventional Si devices, but as expected the current capability of the SiC JFET diminishes with rising temperatures. A DC-DC converter was then designed and built in accordance with the static characteristics of the SiC JFETs that were measured under extremely high ambient temperatures. The converter was tested up to an ambient temperature of 400 degC. The conduction loss of the SiC JFET increases slightly, as predicted from its DC characteristics, but its switching characteristics hardly change with increasing temperatures. Thus, SiC devices are well suited for operation in harsh temperature environments

Extending the ZVS Operating Range of Dual Active Bridge High-Power DC-DC Converters

A switching control strategy to extend the soft-switching operating range of the dual active bridge (DAB) dc-dc converter under the zero-voltage-switching (ZVS) operating mode is proposed. The converter topology consists of two active bridges linked by a high-frequency transformer. One drawback of this strategy is that soft-switching is only possible in a restricted converter operating region. A novel pulse width modulation strategy to extend the conventional soft-switching operating mode region and its analysis are presented in this paper. Experimental results are given in order to validate the theoretical analysis and practical feasibility of the proposed strategy.

The role of ultracapacitors in an energy storage unit for vehicle power management

This paper extends a design methodology for a combined battery-ultracapacitor energy storage unit (BU-ESU) for vehicle power management into two areas. First, the model of the half-bridge converter replaces the generic models of the dc/dc converters used in the BU-ESU. This model is capable of determining the electric stresses present on the active and passive components during the operation of the vehicle. Second, an improved BU-ESU control strategy applicable to all operating conditions of the vehicle is determined. This control strategy is used to resize the BU-ESU. Finally, the vehicle fuel consumptions achieved when using this newly resized BU-ESU are compared using ADVISOR simulation results with those obtained for the BU-ESU designed in R.M. Schupbach et al. (June 2003).

A PV dispersed generator: a power quality analysis within the IEEE 519

The use of environmentally clean photovoltaic (PV) dispersed generation will become more widespread in the future due to anticipated cost reductions in PV technology. This paper summarizes the results of a power quality (PQ) study performed on a PV generator in order to estimate the effects that inverter-interfaced PV dispersed generation might have upon the quality of electric power. Different interpretations of the harmonic distortion limits set in the IEEE 519-1992 standard are performed together with a comparison with the BC Hydros harmonic current limits. This paper also includes a statistical analysis of all measurements recorded with the help of two PQ monitors, an evaluation of the results from a connection/disconnection test, and harmonic simulation results.

Lifetime of Electrolytic Capacitors in Regenerative Induction Motor Drives

Electrolytic capacitors are normally used as the energy storage element in the DC link of voltage-source converters because of their high density. Unfortunately, they are bulky and their lifetime is significantly reduced by their operating temperatures. Thus, reducing, or even better eliminating, the amount of electrolytic capacitors is an important goal since the capacitor could be a single point of failure. This paper analyses the lifetime of electrolytic capacitors used in the DC link of an induction motor (IM) drive whose front end consists of a controlled rectifier. The latter controls the DC-link voltage and input power factor. Both, the inverter and rectifier operate under space vector modulation (SVM). The peak ripple voltage, ripple current, core temperature and lifetime of electrolytic capacitors ranging from 200 muF to 12000 muF are calculated for different values of the source inductance and the ambient temperature when the IM is operating at rated load. In addition, the IM ripple torque and speed response time are also calculated and an 8.2 muF ceramic capacitor case is included for completeness. The evaluation is based on Matlabtrade/Simulink simulation results of the IM drive that are used to calculate harmonic components of the different current waveforms. The results show that the lifetime of electrolytic capacitors is significantly reduced for decreasing capacitance values. The main reason is that the effective series resistance (ESR), and hence heat losses, increases for decreasing capacitance values leading to increased core temperatures that are detrimental to the capacitor lifetime

35 KW ultracapacitor unit for power management of hybrid electric vehicles: bidirectional DC-DC converter design

The work presented in this paper focuses on the design of a half-bridge DC-DC converter for the power electronics interface of energy-storage units for a fuel-cell sport utility vehicle. Several design options are explored; namely: single stage vs. multiple interleaved stages, and continuous vs. discontinuous conduction mode. These design options are weighed against the design goals of minimum cost, high efficiency at low output power levels, and minimum volume and weight to allow for high integration. Special emphasis is given to the impact that the wide input voltage requirements (i.e., from 150 V to 270 V) has on the component stresses.

Power Conversion with SiC Devices at Extremely High Ambient Temperatures

This paper evaluates the capability of SiC devices for operation under extremely high ambient temperatures. To this end, the authors packaged SiC JFET and Schottky barrier diodes (SBD) in thermally stable packages and built a high-temperature inductor to be evaluated in a DC-DC buck converter. The DC characteristics of the SiC JFET devices were first measured at ambient temperatures ranging from room temperature up to 450 degC. The experimental results show that the device can operate at 450 degC, which is impossible for conventional Si devices, but as expected the current capability of the SiC JFET diminishes with rising temperatures. A DC-DC converter was then designed and built in accordance with the static characteristics of the SiC JFETs that were measured under extremely high ambient temperatures. The converter was tested up to an ambient temperature of 400 degC. The conduction loss of the SiC JFET increases slightly, as predicted from its DC characteristics, but its switching characteristics hardly change with increasing temperatures. Thus, SiC devices are well suited for operation in harsh temperature environments

Measurements of neutral currents and voltages on a distribution feeder

Neutral currents flow in four-wire distribution systems due to linear load unbalances and triplen harmonics associated with mainly the magnetizing currents of (distribution) transformers. It is known that high levels of neutral currents can lead to overloaded/burned neutral conductors, common-mode noise problems, derating of transformers and/or excessive voltage distortion. The proliferation of nonlinear loads which inject harmonic currents into the distribution system has brought more attention upon the levels of neutral currents and voltages found in distribution systems. To this end, this paper evaluates measurements taken on the neutral conductors of a distribution feeder at two different sites. The analysis of the measurements focuses on the magnitudes of the triplen-harmonic currents and voltages relative to their corresponding phase RMS values in order to separate the impact on the neutral conductors of nonlinear loads and linear load unbalances.

Placement of energy storage coordinated with smart PV inverters

Energy storage (ES) is increasing used in electrical transmission and distribution systems because it can perform many functions. These include peak shaving, voltage regulation, frequency regulation, spinning reserve, and aiding integration of renewable generation by mitigating the effects of intermittency. This work focuses on the usage of energy storage for peak shaving and voltage regulation on a distribution system having a high penetration of photovoltaic (PV) generation. The PV stations considered make use of smart PV inverters as proposed by the Electric Power Research Institute (EPRI). These inverters assist the energy storage with voltage regulation. Additionally, the proposed method includes support for varying energy storage unit (ESU) sizes, non-radial distribution systems, and reverse power flow, both real and reactive. The method is applied to the worst-case voltage regulation scenario. The impact of the placement and voltage regulation on the profitability of energy storage is assessed. This is accomplished by adding voltage regulation as a constraint to the problem scheduling energy storage in order to maximize profit. Applying the method shows that the best place to put an ESU is near the end of a feeder. Validation of the method shows that it does not impact the ability of ES to be scheduled in order to maximize economic benefits with time-of-use pricing.

A Survey of Systems to Integrate Distributed Energy Resources and Energy Storage on the Utility Grid

Renewable distributed energy resources (DERs) will play a large role in the future energy infrastructure because of advantages like lower carbon imprints, lower fuel costs, and reduced power flows on transmission lines. The unreliability of many renewable DERs due to the intermittent nature of their supply, especially in the case of solar and wind generators, can be mitigated with energy storage that brings a host of additional benefits including load leveling, frequency control, and power quality compensation. One barrier to adoption of these technologies is the need for interfaces between the different voltage levels and waveforms produced by the various systems. This paper, which is tutorial in nature, examines several possible interfaces presented in the literature and provides a comparison between their advantages and disadvantages.