Search

The number of auxiliary electric drives can exceed 100 for luxury cars. Due to their ever‐increasing prevalence, the electromagnetic emissions (EME) of these drives are becoming increasingly important. This work explores the influence of four different stator winding topologies on the electromagnetic emissions and the efficiency performance of fractional horsepower (FHP) brushless direct current (BLDC) drives. Two monofilar windings with a wire diameter of 0.15 and 0.27 mm, an untwisted bifilar winding, and a twisted bifilar winding are inspected. The parasitic stator to winding coupling capacitance is the motor's main source for common mode currents and thus, for radiated emissions. A three‐media capacitance model is introduced to allow estimating this coupling path in the design phase of the motor. Twisting the phases of a bifilar winding reduces the excitation of this path. Therefore, the radiated emissions are reduced by 5 dBμV/m ${\mathrm{B}}_{\mu \text{V/m}}$. The stator winding topology also affects the winding resistance and thus the efficiency. The monofilar winding with a wire diameter of 0.27 mm shows the lowest level of consumed power, followed by the monofilar winding with a wire diameter of 0.15 mm, the untwisted bifilar winding and the twisted bifilar winding. [ABSTRACT FROM AUTHOR]

Ocean energy conversion systems have recently seen renewed interest, stimulated mostly by today's increasing energy discussions. In addition to ocean current energy converters, several commercial ocean wave energy projects have already been undertaken; however, no clear economic model exists for developers to follow. Therefore, this paper focuses on U.S. economic factors that affect the use of wave power for generation of electric energy. These are addressed with regard to economic and business incentives for renewables and wave energy. This paper also investigates incentive programs needed to promote wave energy conversion technology. Index Terms--Ocean renewable energy, wave energy conversion.

The additional high-frequency (HF) common-mode (CM) current of inverter-based drive systems can cause parasitic effects such as HF bearing currents. This HF CM current can be significantly reduced by purpose-designed CM chokes that are inserted in the drive at the inverter output. This paper discusses scaling issues related to the design of such CM chokes, of both wound and feed-through toroidal types. The requirements for the design of chokes for these applications can differ from those for CM chokes designed for use in the inverter input, such as those used for the purpose of electromagnetic interference filtering. This difference is notably due to the comparatively large magnitude of the currents involved. The developed correlations allow taking full advantage of the possibilities offered by such chokes to reduce the HF CM current and mitigate the resultant parasitic effects. The discussed relationships are derived analytically, and the results are supported by measurements. Index Terms--Common-mode (CM) current, CM voltage, converter-machine interactions, variable-speed drives.

Carbon brushes using electrically conductive carbon graphite have been used for shaft-grounding and current-conduction purposes for a long time. We present an alternative brush concept made from millions of conductive microfibers. If properly designed, such brushes can meet all the demands on carbon brushes but exclude the problems of excessive and hot-spotting/thermal wears commonly quoted with the first. These brushes have ultralow friction and negligible wear and are very robust toward contamination, when compared with conventional carbon-based brushes. In addition, they are particularly suitable for use with high-frequency currents and voltages, as they also allow current-conduction based on electric field emission. We develop the design criteria for such brushes, both for prevention of voltage buildup and current conduction of several tens of amperes with frequencies in the megahertz range. We support the theoretical results with measurement results taken at different rotor shaft speed. Index Terms--Bearings (mechanical), common-mode (CM) voltage, electric breakdown, electric field effects, variable-speed drives.

In this survey paper, we show by straightforward mathematical scaling considerations that small inverter-fed ac motors of up to typical 20 kW at 1500/min are likely to suffer from discharge (electric discharge machining) bearing currents, whereas larger motors are likely to be subjected to high-frequency (HF) circulating bearing currents. When comparing motors that operate at the same voltage level, the resulting bearing-current density is high for very small and very large motors. Smaller values occur in between these two extremes with medium size motors in the range of 10-100 kW. Therefore, electric bearing insulation is useful for larger motors to interrupt the HF circulating bearing-current path, whereas small motors need rotor shielding, common-mode voltage filters, or hybrid bearings. Index Terms--Bearings (mechanical), common-mode voltage, currents, failure analysis, inverter-induced bearing, variable-speed drives.

Today, the physical cause-and-effect chains of inverter-induced high-frequency bearing currents have been well understood, but little has been known on not only theoretically possible, but also cost-effective mitigation techniques for a certain drive configuration. This paper focuses on the mitigation of discharge bearing currents, which occur predominantly with smaller motors of up to several kilowatts. We present a new mitigation technique where any voltage build-up across the bearing is discharged via static charge dissipation through a parallel path before an electric breakdown inside the bearing occurs. The technique is based on the field emission effect, has ultralow friction and negligible wear, and is very robust toward contamination, when compared with conventional carbon-based brushes. Index Terms--Bearings (mechanical), common-mode voltage, electric breakdown, electric field effects, variable-speed drives.

Inverter-induced high-frequency bearing currents are a parasitic effect that can occur in variable-speed drive systems. While the physical cause-and-effect chains are understood, little has been known on appropriate quantitative assessment of the phenomena. This paper discusses reliable techniques for the measurement of different parameters of importance for the bearing damage assessment, including their effects on the phenomena and measured quantities. A good understanding of these correlations allows custom-design cost-effective handling of the matter. Index Terms--Common-mode voltage, inverter-induced bearing currents, variable-speed drives.

The influence of different parameters of a variable-speed drive system on the phenomena of inverter-induced bearing currents has been studied under exactly the same conditions on inverter-operated alternating current motors from 1 to 500 kW. Detailed modeling may not always be applicable with practical applications in the field, where many parameters might be unknown. Therefore, the most important correlations are summarized in the form of a flowchart that is based on the physical cause-and-effect chains. This flowchart can serve as a tool for engineers to estimate the endangerment of a drive system due to inverter-induced bearing currents and select an appropriate mitigation technique if necessary, where detailed knowledge of the different design parameters is not available. Index Terms--Bearings (mechanical), failure analysis, fault diagnosis, variable-speed drives.

The occurrence of high-frequency discharge bearing currents (also called 'electric discharge machining (EDM) currents') that can occur in machines of inverter-based drive systems depends strongly on the value of the capacitive voltage divider 'bearing voltage ratio' (BVR) of the machine. This paper presents a straightforward approach to calculate the involved motor capacitances in order to predict the voltage across the bearing and, thereby, the likeliness of such EDM currents that are caused by this voltage to occur. The approach is based on the design parameters of the machine and does not involve additional measurements. It combines ease of application and satisfying accurateness, and allows prediction of the risk of endangerment of an inverter-based drive system due to discharge bearing currents. Index Terms--Bearings (mechanical), failure analysis, variable-speed drives.

The high-frequency circulating bearing current that may occur in machines of inverter-based drive systems can be described by an eddy-current model. The parameters of an equivalent circuit are derived from the model. The ratio between bearing current and common-mode current amplitudes for different machines is calculated. The theoretical maximum ratio is about 0.35. Copper loops applied for bearing current measurement may decrease the circulating bearing currents up to almost 40%. Index Terms--Common-mode voltage, inverter-induced circulating bearing currents, variable-speed drives.